Merge branch 'kvakvs/erts/monitor_port/OTP-11384'

* kvakvs/erts/monitor_port/OTP-11384:
  erts: Add port monitors

14 files changed, 1370 insertions, 450 deletions

diff --git a/erts/doc/src/erlang.xml b/erts/doc/src/erlang.xml
index e0c3fed0c2..fa13e4c142 100644
--- a/erts/doc/src/erlang.xml
+++ b/erts/doc/src/erlang.xml
@@ -2916,107 +2916,105 @@ os_prompt% </pre>
     <func>
       <name name="monitor" arity="2" clause_i="1"/>
       <name name="monitor" arity="2" clause_i="2"/>
+      <name name="monitor" arity="2" clause_i="3"/>
       <fsummary>Starts monitoring.</fsummary>
       <type name="registered_name"/>
       <type name="registered_process_identifier"/>
       <type name="monitor_process_identifier"/>
+      <type name="monitor_port_identifier"/>
       <desc>
-	<p>Send a monitor request of type <c><anno>Type</anno></c> to the
-	entity identified by <c><anno>Item</anno></c>. The caller of
-	<c>monitor/2</c> will later be notified by a monitor message on the
-	following format if the monitored state is changed:</p>
+	<p>Sends a monitor request of type <c><anno>Type</anno></c> to the
+	  entity identified by <c><anno>Item</anno></c>. If the monitored entity
+          does not exist or when it dies, the caller of <c>monitor/2</c> will
+          be notified by a message on the following format:</p>
         <code type="none">{Tag, <anno>MonitorRef</anno>, <anno>Type</anno>, Object, Info}</code>
 	<note><p>The monitor request is an asynchronous signal. That is, it
 	takes time before the signal reaches its destination.</p></note>
-	<p>Valid <c><anno>Type</anno></c>s:</p>
-	<taglist>
-	  <tag><marker id="monitor_process"/><c>process</c></tag>
-	  <item>
-	    <p>Monitor the existence of the process identified by
-	    <c><anno>Item</anno></c>. Valid
-	    <c><anno>Item</anno></c>s in combination with the
-	    <c>process <anno>Type</anno></c> can be any of the following:</p>
-            <taglist>
-              <tag><c>pid()</c></tag>
-              <item>
-		<p>The process identifier of the process to monitor.</p>
-              </item>
-              <tag><c>{RegisteredName, Node}</c></tag>
-              <item>
-		<p>A tuple consisting of a registered name of a process and
-		a node name. The process residing on the node <c>Node</c>
-		with the registered name <c>{RegisteredName, Node}</c> will
-		be monitored.</p>
-              </item>
-              <tag><c>RegisteredName</c></tag>
-              <item>
-		<p>The process locally registered as <c>RegisteredName</c>
-		will become monitored.</p>
-              </item>
-            </taglist>
-            <note><p>When a registered name is used, the
-	    process that has the registered name when the
-            monitor request reach its destination will be monitored.
-            The monitor is not effected if the registered name is
-            unregistered, or unregistered and later registered on another
-	    process.</p></note>
-	    <p>The monitor is triggered either when the monitored process
-	    terminates, is non existing, or if the connection to it is
-	    lost. In the case the connection to it is lost, we do not know
-	    if it still exist or not. After this type of monitor has been
-	    triggered, the monitor is automatically removed.</p>
-            <p>When the monitor is triggered a <c>'DOWN'</c> message is
-	    sent to the monitoring process. A <c>'DOWN'</c> message has
-	    the following pattern:</p>
-            <code type="none">{'DOWN', MonitorRef, Type, Object, Info}</code>
-            <p>Here <c>MonitorRef</c> and <c>Type</c> are the same as
-            described earlier, and:</p>
-            <taglist>
-              <tag><c>Object</c></tag>
-              <item>
-		<p>equals:</p>
-		<taglist>
-		  <tag><c><anno>Item</anno></c></tag>
-		  <item>If <c><anno>Item</anno></c> is specified by a
-		  process identifier.</item>
-		  <tag><c>{RegisteredName, Node}</c></tag>
-		  <item>If <c><anno>Item</anno></c> is specified as
-		  <c>RegisteredName</c>, or <c>{RegisteredName, Node}</c>
-		  where <c>Node</c> corresponds to the node that the
-		  monitored process resides on.</item>
-		</taglist>
-              </item>
-              <tag><c>Info</c></tag>
-              <item>
-		<p>Either the exit reason of the process, <c>noproc</c>
-		(non-existing process), or <c>noconnection</c> (no
-		connection to the node where the monitored process
-		resides).</p></item>
-	    </taglist>
-	    <p>The monitoring is turned off when the <c>'DOWN'</c>
-	    message is sent or when
-	    <seealso marker="#demonitor/1">demonitor/1</seealso>
-	    is called.</p>
-	    <p>If an attempt is made to monitor a process on an older node
-	    (where remote process monitoring is not implemented or
-	    where remote process monitoring by registered name is not
-	    implemented), the call fails with <c>badarg</c>.</p>
-	    <note>
-	      <p>The format of the <c>'DOWN'</c> message changed in ERTS
-	      version 5.2 (OTP R9B) for monitoring
-	      <em>by registered name</em>. Element <c>Object</c> of
-	      the <c>'DOWN'</c> message could in earlier versions
-	      sometimes be the process identifier of the monitored process and sometimes
-	      be the registered name. Now element <c>Object</c> is
-	      always a tuple consisting of the registered name and
-	      the node name. Processes on new nodes (ERTS version 5.2
-	      or higher) always get <c>'DOWN'</c> messages on
-	      the new format even if they are monitoring processes on old
-	      nodes. Processes on old nodes always get <c>'DOWN'</c>
-	      messages on the old format.</p>
-	    </note>
-	  </item>
-	  <tag><marker id="monitor_time_offset"/><c>time_offset</c></tag>
+
+        <p><c><anno>Type</anno></c> can be one of the following atoms:
+          <c>process</c>, <c>port</c> or <c>time_offset</c>.</p>
+
+        <p>A monitor is triggered only once, after that it is removed from
+          both monitoring process and the monitored entity.
+          Monitors are fired when the monitored process or port terminates,
+          does not exist at the moment of creation, or if the connection to
+          it is lost. In the case with connection, we lose knowledge about
+          the fact if it still exists or not. The monitoring is also turned off
+          when <seealso marker="#demonitor/1">demonitor/1</seealso>
+          is called.</p>
+
+        <p>When monitoring by name please note, that the <c>RegisteredName</c>
+          is resolved to <c>pid()</c> or <c>port()</c> only once
+          at the moment of monitor instantiation, later changes to the name
+          registration will not affect the existing monitor.</p>
+
+        <p>When a monitor is triggered, a <c>'DOWN'</c> message that has the
+          following pattern <c>{'DOWN', MonitorRef, Type, Object, Info}</c>
+          is sent to the monitoring process.</p>
+
+        <p>In monitor message <c>MonitorRef</c> and <c>Type</c> are the same as
+          described earlier, and:</p>
+        <taglist>
+          <tag><c>Object</c></tag>
+          <item>
+            <p>The monitored entity, which triggered the event. When monitoring
+              a local process or port, <c>Object</c> will be equal to the
+              <c>pid()</c> or <c>port()</c> that was being monitored. When
+              monitoring process or port by name, <c>Object</c> will have format
+              <c>{RegisteredName, Node}</c> where <c>RegisteredName</c> is the
+              name which has been used with <c>monitor/2</c> call and
+              <c>Node</c> is local or remote node name (for ports monitored by
+              name, <c>Node</c> is always local node name).</p>
+          </item>
+          <tag><c>Info</c></tag>
+          <item>
+            <p>Either the exit reason of the process, <c>noproc</c>
+              (process or port did not exist at the time of monitor creation),
+              or <c>noconnection</c> (no connection to the node where the
+              monitored process resides). </p></item>
+        </taglist>
+
+        <p>If an attempt is made to monitor a process on an older node
+          (where remote process monitoring is not implemented or
+          where remote process monitoring by registered name is not
+          implemented), the call fails with <c>badarg</c>.</p>
+        <note>
+          <p>The format of the <c>'DOWN'</c> message changed in ERTS
+            version 5.2 (OTP R9B) for monitoring
+            <em>by registered name</em>. Element <c>Object</c> of
+            the <c>'DOWN'</c> message could in earlier versions
+            sometimes be the process identifier of the monitored process and sometimes
+            be the registered name. Now element <c>Object</c> is
+            always a tuple consisting of the registered name and
+            the node name. Processes on new nodes (ERTS version 5.2
+            or higher) always get <c>'DOWN'</c> messages on
+            the new format even if they are monitoring processes on old
+            nodes. Processes on old nodes always get <c>'DOWN'</c>
+            messages on the old format.</p>
+        </note>
+
+        <taglist>
+        <tag>Monitoring a <marker id="monitor_process"/><c>process</c></tag>
+        <item>
+        <p>Creates monitor between the current process and another
+          process identified by <c><anno>Item</anno></c>, which can be a
+          <c>pid()</c> (local or remote), an atom <c>RegisteredName</c> or
+          a tuple <c>{RegisteredName, Node}</c> for a registered process,
+          located elsewhere.</p>
+        </item>
+
+        <tag>Monitoring a <marker id="monitor_port"/><c>port</c></tag>
+        <item>
+          <p>Creates monitor between the current process and a port
+            identified by <c><anno>Item</anno></c>, which can be a
+            <c>port()</c> (only local), an atom <c>RegisteredName</c> or
+            a tuple <c>{RegisteredName, Node}</c> for a registered port,
+            located on this node. Note, that attempt to monitor a remote port
+            will result in <c>badarg</c>.</p>
+        </item>
+
+        <tag>Monitoring a
+          <marker id="monitor_time_offset"/><c>time_offset</c></tag>
 	  <item>
 	    <p>Monitor changes in
 	    <seealso marker="#time_offset/0">time offset</seealso>
@@ -3072,15 +3070,17 @@ os_prompt% </pre>
 	    Note that you can observe the change of the time offset
 	    when calling <c>erlang:time_offset()</c> before you
 	    get the <c>'CHANGE'</c> message.</p>
-
 	  </item>
 	</taglist>
+
 	<p>Making several calls to <c>monitor/2</c> for the same
-	<c><anno>Item</anno></c> and/or <c><anno>Type</anno></c> is not
-	an error; it results in as many independent monitoring instances.</p>
+	  <c><anno>Item</anno></c> and/or <c><anno>Type</anno></c> is not
+	  an error; it results in as many independent monitoring instances.</p>
+
 	<p>The monitor functionality is expected to be extended. That is,
-	other <c><anno>Type</anno></c>s and <c><anno>Item</anno></c>s
-	are expected to be supported in	a future release.</p>
+	  other <c><anno>Type</anno></c>s and <c><anno>Item</anno></c>s
+	  are expected to be supported in a future release.</p>
+
         <note>
           <p>If or when <c>monitor/2</c> is extended, other
             possible values for <c>Tag</c>, <c>Object</c> and
@@ -4150,6 +4150,22 @@ os_prompt% </pre>
 
     <func>
       <name name="port_info" arity="2" clause_i="8"/>
+      <fsummary>Which processes are monitoring this port.</fsummary>
+      <desc>
+        <p>Returns list of pids that are monitoring given port at the
+          moment.</p>
+        <p>If the port identified by <c><anno>Port</anno></c> is not open,
+          <c>undefined</c> is returned. If the port is closed and the
+          calling process was previously linked to the port, the exit
+          signal from the port is guaranteed to be delivered before
+          <c>port_info/2</c> returns <c>undefined</c>.</p>
+        <p>Failure: <c>badarg</c> if <c><anno>Port</anno></c> is not a local
+          port identifier, or an atom.</p>
+      </desc>
+    </func>
+
+    <func>
+      <name name="port_info" arity="2" clause_i="9"/>
       <fsummary>Information about the name of a port.</fsummary>
       <desc>
 	<p><c><anno>Name</anno></c> is the command name set by
@@ -4165,7 +4181,7 @@ os_prompt% </pre>
     </func>
 
     <func>
-      <name name="port_info" arity="2" clause_i="9"/>
+      <name name="port_info" arity="2" clause_i="10"/>
       <fsummary>Information about the OS pid of a port.</fsummary>
       <desc>
 	<p><c><anno>OsPid</anno></c> is the process identifier (or equivalent)
@@ -4184,7 +4200,7 @@ os_prompt% </pre>
     </func>
 
     <func>
-      <name name="port_info" arity="2" clause_i="10"/>
+      <name name="port_info" arity="2" clause_i="11"/>
       <fsummary>Information about the output of a port.</fsummary>
       <desc>
 	<p><c><anno>Bytes</anno></c> is the total number of bytes written
@@ -4203,7 +4219,7 @@ os_prompt% </pre>
     </func>
 
     <func>
-      <name name="port_info" arity="2" clause_i="11"/>
+      <name name="port_info" arity="2" clause_i="12"/>
       <fsummary>Information about the parallelism hint of a port.</fsummary>
       <desc>
 	<p><c><anno>Boolean</anno></c> corresponds to the port parallelism
@@ -4214,7 +4230,7 @@ os_prompt% </pre>
     </func>
 
     <func>
-      <name name="port_info" arity="2" clause_i="12"/>
+      <name name="port_info" arity="2" clause_i="13"/>
       <fsummary>Information about the queue size of a port.</fsummary>
       <desc>
 	<p><c><anno>Bytes</anno></c> is the total number
@@ -4231,7 +4247,7 @@ os_prompt% </pre>
     </func>
 
     <func>
-      <name name="port_info" arity="2" clause_i="13"/>
+      <name name="port_info" arity="2" clause_i="14"/>
       <fsummary>Information about the registered name of a port.</fsummary>
       <desc>
 	<p><c><anno>RegisteredName</anno></c> is the registered name of
@@ -4865,10 +4881,19 @@ os_prompt% </pre>
             <p>A list of monitors (started by <c>monitor/2</c>)
               that are active for the process. For a local process
               monitor or a remote process monitor by a process
-              identifier, the list item is <c>{process, <anno>Pid</anno>}</c>.
-              For a remote process
-              monitor by name, the list item is
-              <c>{process, {<anno>RegName</anno>, <anno>Node</anno>}}</c>.</p>
+              identifier, the list consists of:</p>
+              <taglist>
+                <tag><c>{process, <anno>Pid</anno>}</c></tag>
+                <item>Process is monitored by pid.</item>
+                <tag><c>{process, {<anno>RegName</anno>, <anno>Node</anno>}}</c></tag>
+                <item>Local or remote process is monitored by name.</item>
+                <tag><c>{port, PortId}</c></tag>
+                <item>Local port is monitored by port id.</item>
+                <tag><c>{port, {<anno>RegName</anno>, <anno>Node</anno>}}</c></tag>
+                <item>Local port is monitored by name. Please note, that
+                  remote port monitors are not supported, so <c>Node</c> will
+                  always be the local node name.</item>
+              </taglist>
           </item>
           <tag><c>{message_queue_data, <anno>MQD</anno>}</c></tag>
           <item>
diff --git a/erts/emulator/beam/bif.c b/erts/emulator/beam/bif.c
index b18910e2c7..fc14061a44 100644
--- a/erts/emulator/beam/bif.c
+++ b/erts/emulator/beam/bif.c
@@ -282,20 +282,17 @@ res_no_proc: {
     }
 }
 
-#define ERTS_DEMONITOR_FALSE		2
-#define ERTS_DEMONITOR_TRUE		1
-#define ERTS_DEMONITOR_BADARG		0
-#define ERTS_DEMONITOR_YIELD_TRUE	-1
-#define ERTS_DEMONITOR_INTERNAL_ERROR	-2
-
-static int
+/* This function is allowed to return range of values handled by demonitor/1-2
+ * Namely: atoms true, false, yield, internal_error, badarg or THE_NON_VALUE
+ */
+static Eterm
 remote_demonitor(Process *c_p, DistEntry *dep, Eterm ref, Eterm to)
 {
     ErtsDSigData dsd;
     ErtsMonitor *dmon;
     ErtsMonitor *mon;
     int code;
-    int res;
+    Eterm res = am_false;
 #ifndef ERTS_SMP
     int stale_mon = 0;
 #endif
@@ -328,7 +325,7 @@ remote_demonitor(Process *c_p, DistEntry *dep, Eterm ref, Eterm to)
 	mon = erts_remove_monitor(&ERTS_P_MONITORS(c_p), ref);
 	erts_smp_proc_unlock(c_p, ERTS_PROC_LOCK_LINK);
 
-	res = ERTS_DEMONITOR_TRUE;
+        res = am_true;
 	break;
 
     case ERTS_DSIG_PREP_CONNECTED:
@@ -352,7 +349,7 @@ remote_demonitor(Process *c_p, DistEntry *dep, Eterm ref, Eterm to)
 	     * This is possible when smp support is enabled.
 	     * 'DOWN' message just arrived.
 	     */
-	    res = ERTS_DEMONITOR_TRUE;
+            res = am_true;
 	}
 	else {
 	    /*
@@ -367,16 +364,13 @@ remote_demonitor(Process *c_p, DistEntry *dep, Eterm ref, Eterm to)
 					     : mon->pid), 
 					    ref,
 					    0);
-	    res = (code == ERTS_DSIG_SEND_YIELD
-		   ? ERTS_DEMONITOR_YIELD_TRUE
-		   : ERTS_DEMONITOR_TRUE);
+            res = (code == ERTS_DSIG_SEND_YIELD ? am_yield : am_true);
 	    erts_destroy_monitor(dmon);
-
 	}
 	break;
     default:
 	ASSERT(! "Invalid dsig prepare result");
-	return ERTS_DEMONITOR_INTERNAL_ERROR;
+        return am_internal_error;
     }
 
 #ifndef ERTS_SMP
@@ -404,27 +398,96 @@ remote_demonitor(Process *c_p, DistEntry *dep, Eterm ref, Eterm to)
     return res;
 }
 
-static int demonitor(Process *c_p, Eterm ref, Eterm *multip)
+static ERTS_INLINE void
+demonitor_local_process(Process *c_p, Eterm ref, Eterm to, Eterm *res)
+{
+    Process *rp = erts_pid2proc_opt(c_p,
+                           ERTS_PROC_LOCK_MAIN|ERTS_PROC_LOCK_LINK,
+                           to,
+                           ERTS_PROC_LOCK_LINK,
+                           ERTS_P2P_FLG_ALLOW_OTHER_X);
+    ErtsMonitor *mon = erts_remove_monitor(&ERTS_P_MONITORS(c_p), ref);
+
+#ifndef ERTS_SMP
+    ASSERT(mon);
+#else
+    if (!mon)
+        *res = am_false;
+    else
+#endif
+    {
+        *res = am_true;
+        erts_destroy_monitor(mon);
+    }
+    if (rp) {
+        ErtsMonitor *rmon;
+        rmon = erts_remove_monitor(&ERTS_P_MONITORS(rp), ref);
+        if (rp != c_p)
+            erts_smp_proc_unlock(rp, ERTS_PROC_LOCK_LINK);
+        if (rmon != NULL)
+            erts_destroy_monitor(rmon);
+    }
+    else {
+        ERTS_SMP_ASSERT_IS_NOT_EXITING(c_p);
+    }
+}
+
+static ERTS_INLINE BIF_RETTYPE
+demonitor_local_port(Process *origin, Eterm ref, Eterm target)
 {
-   ErtsMonitor *mon = NULL;  /* The monitor entry to delete */
-   Process  *rp;    /* Local target process */
-   Eterm     to = NIL;    /* Monitor link traget */
-   DistEntry *dep = NULL;  /* Target's distribution entry */
-   int deref_de = 0;
-   int res;
-   int unlock_link = 1;
+    BIF_RETTYPE res = am_false;
+    Port        *port = erts_port_lookup_raw(target);
+
+    if (!port) {
+        BIF_ERROR(origin, BADARG);
+    }
+    erts_smp_proc_unlock(origin, ERTS_PROC_LOCK_LINK);
+
+    if (port) {
+        Eterm trap_ref;
+        switch (erts_port_demonitor(origin, ERTS_PORT_DEMONITOR_NORMAL,
+                                    port, ref, &trap_ref)) {
+        case ERTS_PORT_OP_DROPPED:
+        case ERTS_PORT_OP_BADARG:
+            break;
+        case ERTS_PORT_OP_SCHEDULED:
+            BIF_TRAP3(await_port_send_result_trap, origin, trap_ref,
+                      am_busy_port, am_true);
+            /* the busy_port atom will never be returned, because it cannot be
+             * returned from erts_port_(de)monitor, but just in case if in future
+             * internal API changes - you may see this atom */
+        default:
+            break;
+        }
+    }
+    else {
+        ERTS_SMP_ASSERT_IS_NOT_EXITING(origin);
+    }
+    BIF_RET(res);
+}
 
+/* Can return atom true, false, yield, internal_error, badarg or
+ * THE_NON_VALUE if error occured or trap has been set up
+ */
+static
+BIF_RETTYPE demonitor(Process *c_p, Eterm ref, Eterm *multip)
+{
+   ErtsMonitor  *mon = NULL;  /* The monitor entry to delete */
+   Eterm        to = NIL;     /* Monitor link traget */
+   DistEntry    *dep = NULL;  /* Target's distribution entry */
+   int          deref_de = 0;
+   BIF_RETTYPE  res = am_false;
+   int          unlock_link = 1;
 
    erts_smp_proc_lock(c_p, ERTS_PROC_LOCK_LINK);
 
    if (is_not_internal_ref(ref)) {
-       res = ERTS_DEMONITOR_BADARG;
+       res = am_badarg;
        goto done; /* Cannot be this monitor's ref */
    }
 
    mon = erts_lookup_monitor(ERTS_P_MONITORS(c_p), ref);
    if (!mon) {
-       res = ERTS_DEMONITOR_FALSE;
        goto done;
    }
 
@@ -432,70 +495,50 @@ static int demonitor(Process *c_p, Eterm ref, Eterm *multip)
    case MON_TIME_OFFSET:
        *multip = am_true;
        erts_demonitor_time_offset(ref);
-       res = ERTS_DEMONITOR_TRUE;
+       res = am_true;
        break;
    case MON_ORIGIN:
        to = mon->pid;
        *multip = am_false;
        if (is_atom(to)) {
-	   /* Monitoring a name at node to */
-	   ASSERT(is_node_name_atom(to));
-	   dep = erts_sysname_to_connected_dist_entry(to);
-	   ASSERT(dep != erts_this_dist_entry);
-	   if (dep)
-	       deref_de = 1;
+           /* Monitoring a name at node to */
+           ASSERT(is_node_name_atom(to));
+           dep = erts_sysname_to_connected_dist_entry(to);
+           ASSERT(dep != erts_this_dist_entry);
+           if (dep)
+               deref_de = 1;
+       } else if (is_port(to)) {
+           if (port_dist_entry(to) != erts_this_dist_entry) {
+               goto badarg;
+           }
+           res = demonitor_local_port(c_p, ref, to);
+           unlock_link = 0;
+           goto done;
        } else {
-	   ASSERT(is_pid(to));
-	   dep = pid_dist_entry(to);
+           ASSERT(is_pid(to));
+           dep = pid_dist_entry(to);
        }
        if (dep != erts_this_dist_entry) {
-	   res = remote_demonitor(c_p, dep, ref, to);
-	   /* remote_demonitor() unlocks link lock on c_p */
-	   unlock_link = 0;
+           res = remote_demonitor(c_p, dep, ref, to);
+           /* remote_demonitor() unlocks link lock on c_p */
+           unlock_link = 0;
        }
        else { /* Local monitor */
-	   if (deref_de) {
-	       deref_de = 0;
-	       erts_deref_dist_entry(dep);
-	   }
-	   dep = NULL;
-	   rp = erts_pid2proc_opt(c_p,
-				  ERTS_PROC_LOCK_MAIN|ERTS_PROC_LOCK_LINK,
-				  to,
-				  ERTS_PROC_LOCK_LINK,
-				  ERTS_P2P_FLG_ALLOW_OTHER_X);
-	   mon = erts_remove_monitor(&ERTS_P_MONITORS(c_p), ref);
-#ifndef ERTS_SMP
-	   ASSERT(mon);
-#else
-	   if (!mon)
-	       res = ERTS_DEMONITOR_FALSE;
-	   else
-#endif
-	   {
-	       res = ERTS_DEMONITOR_TRUE;
-	       erts_destroy_monitor(mon);
-	   }
-	   if (rp) {
-	       ErtsMonitor *rmon;
-	       rmon = erts_remove_monitor(&ERTS_P_MONITORS(rp), ref);
-	       if (rp != c_p)
-		   erts_smp_proc_unlock(rp, ERTS_PROC_LOCK_LINK);
-	       if (rmon != NULL)
-		   erts_destroy_monitor(rmon);
-	   }
-	   else {
-	       ERTS_SMP_ASSERT_IS_NOT_EXITING(c_p);
-	   }
-
+           if (deref_de) {
+               deref_de = 0;
+               erts_deref_dist_entry(dep);
+           }
+           dep = NULL;
+           demonitor_local_process(c_p, ref, to, &res);
        }
        break;
-   default:
-       res = ERTS_DEMONITOR_BADARG;
+    default /* case */ :
+badarg:
+       res = am_badarg; /* will be converted to error by caller */
        *multip = am_false;
        break;
    }
- done:
+done:
 
    if (unlock_link)
        erts_smp_proc_unlock(c_p, ERTS_PROC_LOCK_LINK);
@@ -506,21 +549,20 @@ static int demonitor(Process *c_p, Eterm ref, Eterm *multip)
    }
 
    ERTS_SMP_LC_ASSERT(ERTS_PROC_LOCK_MAIN == erts_proc_lc_my_proc_locks(c_p));
-   return res;
+   BIF_RET(res);
 }
 
 BIF_RETTYPE demonitor_1(BIF_ALIST_1)
 {
     Eterm multi;
     switch (demonitor(BIF_P, BIF_ARG_1, &multi)) {
-    case ERTS_DEMONITOR_FALSE:
-    case ERTS_DEMONITOR_TRUE:
-	BIF_RET(am_true);
-    case ERTS_DEMONITOR_YIELD_TRUE:
-	ERTS_BIF_YIELD_RETURN(BIF_P, am_true);
-    case ERTS_DEMONITOR_BADARG:
-	BIF_ERROR(BIF_P, BADARG);
-    case ERTS_DEMONITOR_INTERNAL_ERROR:
+    case am_false:
+    case am_true:       BIF_RET(am_true);
+    case THE_NON_VALUE: BIF_RET(THE_NON_VALUE);
+    case am_yield:      ERTS_BIF_YIELD_RETURN(BIF_P, am_true);
+    case am_badarg:     BIF_ERROR(BIF_P, BADARG);
+
+    case am_internal_error:
     default:
 	ASSERT(! "demonitor(): internal error");
 	BIF_ERROR(BIF_P, EXC_INTERNAL_ERROR);
@@ -529,11 +571,11 @@ BIF_RETTYPE demonitor_1(BIF_ALIST_1)
 
 BIF_RETTYPE demonitor_2(BIF_ALIST_2)
 {
-    Eterm res = am_true;
-    Eterm multi = am_false;
-    int info = 0;
-    int flush = 0;
-    Eterm list = BIF_ARG_2;
+    BIF_RETTYPE res = am_true;
+    Eterm       multi = am_false;
+    int         info = 0;
+    int         flush = 0;
+    Eterm       list = BIF_ARG_2;
 
     while (is_list(list)) {
 	Eterm* consp = list_val(list);
@@ -554,24 +596,27 @@ BIF_RETTYPE demonitor_2(BIF_ALIST_2)
 	goto badarg;
 
     switch (demonitor(BIF_P, BIF_ARG_1, &multi)) {
-    case ERTS_DEMONITOR_FALSE:
+    case THE_NON_VALUE:
+        /* If other error occured or trap has been set up - pass through */
+        BIF_RET(THE_NON_VALUE);
+    case am_false:
 	if (info)
 	    res = am_false;
 	if (flush) {
-	flush_messages:
+flush_messages:
 	    BIF_TRAP3(flush_monitor_messages_trap, BIF_P,
 		      BIF_ARG_1, multi, res);
 	}
-    case ERTS_DEMONITOR_TRUE:
+    case am_true:
 	if (multi == am_true && flush)
 	    goto flush_messages;
 	BIF_RET(res);
-    case ERTS_DEMONITOR_YIELD_TRUE:
+    case am_yield:
 	ERTS_BIF_YIELD_RETURN(BIF_P, am_true);
-    case ERTS_DEMONITOR_BADARG:
-    badarg:
+    case am_badarg:
+badarg:
 	BIF_ERROR(BIF_P, BADARG);
-    case ERTS_DEMONITOR_INTERNAL_ERROR:
+    case am_internal_error:
     default:
 	ASSERT(! "demonitor(): internal error");
 	BIF_ERROR(BIF_P, EXC_INTERNAL_ERROR);
@@ -615,14 +660,13 @@ erts_queue_monitor_message(Process *p,
     erts_queue_message(p, *p_locksp, msgp, tup, am_system);
 }
 
-static BIF_RETTYPE
+static Eterm
 local_pid_monitor(Process *p, Eterm target, Eterm mon_ref, int boolean)
 {
-    BIF_RETTYPE ret;
-    Process *rp;
+    Eterm         ret = mon_ref;
+    Process      *rp;
     ErtsProcLocks p_locks = ERTS_PROC_LOCK_MAIN|ERTS_PROC_LOCK_LINK;
 
-    ERTS_BIF_PREP_RET(ret, mon_ref);
     if (target == p->common.id) {
 	return ret;
     }
@@ -658,40 +702,112 @@ local_pid_monitor(Process *p, Eterm target, Eterm mon_ref, int boolean)
 }
 
 static BIF_RETTYPE
-local_name_monitor(Process *p, Eterm target_name)
+local_port_monitor(Process *origin, Eterm target)
 {
-    BIF_RETTYPE ret;
-    Eterm mon_ref;
-    ErtsProcLocks p_locks = ERTS_PROC_LOCK_MAIN|ERTS_PROC_LOCK_LINK;
-    Process *rp;
+    BIF_RETTYPE ref = erts_make_ref(origin);
+    Port *port = erts_sig_lookup_port(origin, target);
+    ErtsProcLocks p_locks = ERTS_PROC_LOCK_MAIN;
 
-    mon_ref = erts_make_ref(p);
-    ERTS_BIF_PREP_RET(ret, mon_ref);
-    erts_smp_proc_lock(p, ERTS_PROC_LOCK_LINK);
-    rp = erts_whereis_process(p, p_locks, target_name, ERTS_PROC_LOCK_LINK,
-			      ERTS_P2P_FLG_ALLOW_OTHER_X);
-    if (!rp) {
-	DeclareTmpHeap(lhp,3,p);
+    if (!port) {
+res_no_proc:
+        /* Send the DOWN message immediately. Ref is made on the fly because
+         * caller has never seen it yet. */
+        erts_queue_monitor_message(origin, &p_locks, ref,
+                                   am_port, target, am_noproc);
+    }
+    else {
+        switch (erts_port_monitor(origin, port, target, &ref)) {
+        case ERTS_PORT_OP_DROPPED:
+        case ERTS_PORT_OP_BADARG:
+            goto res_no_proc;
+        case ERTS_PORT_OP_SCHEDULED:
+            BIF_TRAP3(await_port_send_result_trap, origin, ref,
+                      am_busy_port, ref);
+            /* the busy_port atom will never be returned, because it cannot be
+             * returned from erts_port_monitor, but just in case if in future
+             * internal API changes - you may see this atom */
+        default:
+            break;
+        }
+    }
+    erts_smp_proc_unlock(origin, p_locks & ~ERTS_PROC_LOCK_MAIN);
+    BIF_RET(ref);
+}
+
+/* Type = process | port :: atom(), 1st argument passed to erlang:monitor/2
+ */
+static BIF_RETTYPE
+local_name_monitor(Process *self, Eterm type, Eterm target_name)
+{
+    BIF_RETTYPE ret = erts_make_ref(self);
+
+    ErtsProcLocks p_locks = ERTS_PROC_LOCK_MAIN | ERTS_PROC_LOCK_LINK;
+    Process     *proc = NULL;
+    Port        *port = NULL;
+
+    erts_smp_proc_lock(self, ERTS_PROC_LOCK_LINK);
+
+    erts_whereis_name(self, p_locks, target_name,
+                      &proc, ERTS_PROC_LOCK_LINK,
+                      ERTS_P2P_FLG_ALLOW_OTHER_X,
+                      &port, 0);
+
+    /* If the name is not registered,
+     * or if we asked for proc and got a port,
+     * or if we asked for port and got a proc,
+     * we just send the 'DOWN' message.
+     */
+    if ((!proc && !port) ||
+        (type == am_process && port) ||
+        (type == am_port && proc)) {
+        DeclareTmpHeap(lhp,3,self);
 	Eterm item;
-	UseTmpHeap(3,p);
-	erts_smp_proc_unlock(p, ERTS_PROC_LOCK_LINK);
+        UseTmpHeap(3,self);
+
+        erts_smp_proc_unlock(self, ERTS_PROC_LOCK_LINK);
 	p_locks &= ~ERTS_PROC_LOCK_LINK;
+
 	item = TUPLE2(lhp, target_name, erts_this_dist_entry->sysname);
-	erts_queue_monitor_message(p, &p_locks,
-				   mon_ref, am_process, item, am_noproc);
-	UnUseTmpHeap(3,p);
-    }
-    else if (rp != p) {
-	erts_add_monitor(&ERTS_P_MONITORS(p), MON_ORIGIN, mon_ref, rp->common.id,
-			 target_name);
-	erts_add_monitor(&ERTS_P_MONITORS(rp), MON_TARGET, mon_ref, p->common.id,
-			 target_name);
-	erts_smp_proc_unlock(rp, ERTS_PROC_LOCK_LINK);
+        erts_queue_monitor_message(self, &p_locks,
+                                   ret,
+                                   type, /* = process|port :: atom() */
+                                   item, am_noproc);
+        UnUseTmpHeap(3,self);
+    }
+    else if (port) {
+        erts_smp_proc_unlock(self, p_locks & ~ERTS_PROC_LOCK_MAIN);
+        p_locks &= ~ERTS_PROC_LOCK_MAIN;
+
+        switch (erts_port_monitor(self, port, target_name, &ret)) {
+        case ERTS_PORT_OP_DONE:
+            return ret;
+        case ERTS_PORT_OP_SCHEDULED: { /* Scheduled a signal */
+            ASSERT(is_internal_ref(ret));
+            BIF_TRAP3(await_port_send_result_trap, self,
+                      ret, am_true, ret);
+            /* bif_trap returns */
+        } break;
+        default:
+            goto badarg;
+        }
+    }
+    else if (proc != self) {
+        erts_add_monitor(&ERTS_P_MONITORS(self), MON_ORIGIN, ret,
+                         proc->common.id, target_name);
+        erts_add_monitor(&ERTS_P_MONITORS(proc), MON_TARGET, ret,
+                         self->common.id, target_name);
+        erts_smp_proc_unlock(proc, ERTS_PROC_LOCK_LINK);
     }
 
-    erts_smp_proc_unlock(p, p_locks & ~ERTS_PROC_LOCK_MAIN);
-
-    return ret;
+    if (p_locks) {
+        erts_smp_proc_unlock(self, p_locks & ~ERTS_PROC_LOCK_MAIN);
+    }
+    BIF_RET(ret);
+badarg:
+    if (p_locks) {
+        erts_smp_proc_unlock(self, p_locks & ~ERTS_PROC_LOCK_MAIN);
+    }
+    BIF_ERROR(self, BADARG);
 }
 
 static BIF_RETTYPE
@@ -758,7 +874,7 @@ remote_monitor(Process *p, Eterm bifarg1, Eterm bifarg2,
 	break;
     }
 
-    return ret;
+    BIF_RET(ret);
 }
 	
 BIF_RETTYPE monitor_2(BIF_ALIST_2)
@@ -772,8 +888,9 @@ BIF_RETTYPE monitor_2(BIF_ALIST_2)
     switch (BIF_ARG_1) {
     case am_time_offset: {
 	Eterm ref;
-	if (BIF_ARG_2 != am_clock_service)
-	    goto error;
+        if (BIF_ARG_2 != am_clock_service) {
+            goto badarg;
+        }
 	ref = erts_make_ref(BIF_P);
 	erts_smp_proc_lock(BIF_P, ERTS_PROC_LOCK_LINK);
 	erts_add_monitor(&ERTS_P_MONITORS(BIF_P), MON_TIME_OFFSET,
@@ -783,46 +900,57 @@ BIF_RETTYPE monitor_2(BIF_ALIST_2)
 	BIF_RET(ref);
     }
     case am_process:
+    case am_port:
 	break;
     default:
-	goto error;
+        goto badarg;
     }
 
-    if (is_internal_pid(target)) {
-    local_pid:
-	ret = local_pid_monitor(BIF_P, target, erts_make_ref(BIF_P), 0);
-    } else if (is_external_pid(target)) {
+    if (is_internal_pid(target) && BIF_ARG_1 == am_process) {
+local_pid:
+        ret = local_pid_monitor(BIF_P, target, erts_make_ref(BIF_P), 0);
+    } else if (is_external_pid(target) && BIF_ARG_1 == am_process) {
 	dep = external_pid_dist_entry(target);
 	if (dep == erts_this_dist_entry)
 	    goto local_pid;
 	ret = remote_monitor(BIF_P, BIF_ARG_1, BIF_ARG_2, dep, target, 0);
+    } else if (is_internal_port(target) && BIF_ARG_1 == am_port) {
+local_port:
+        ret = local_port_monitor(BIF_P, target);
+    } else if (is_external_port(target) && BIF_ARG_1 == am_port) {
+        dep = external_port_dist_entry(target);
+        if (dep == erts_this_dist_entry) {
+            goto local_port;
+        }
+        goto badarg; /* No want remote port */
     } else if (is_atom(target)) {
-	ret = local_name_monitor(BIF_P, target);
+        ret = local_name_monitor(BIF_P, BIF_ARG_1, target);
     } else if (is_tuple(target)) {
 	Eterm *tp = tuple_val(target);
 	Eterm remote_node;
 	Eterm name;
-	if (arityval(*tp) != 2) 
-	    goto error;
+        if (arityval(*tp) != 2) {
+            goto badarg;
+        }
 	remote_node = tp[2];
 	name = tp[1];
 	if (!is_atom(remote_node) || !is_atom(name)) {
-	    goto error;
+            goto badarg;
 	}
 	if (!erts_is_alive && remote_node != am_Noname) {
-	    goto error; /* Remote monitor from (this) undistributed node */
+            goto badarg; /* Remote monitor from (this) undistributed node */
 	}
 	dep = erts_sysname_to_connected_dist_entry(remote_node);
 	if (dep == erts_this_dist_entry) {
 	    deref_de = 1;
-	    ret = local_name_monitor(BIF_P, name);
+            ret = local_name_monitor(BIF_P, BIF_ARG_1, name);
 	} else {
 	    if (dep)
 		deref_de = 1;
 	    ret = remote_monitor(BIF_P, BIF_ARG_1, BIF_ARG_2, dep, name, 1);
 	}
     } else {
-    error:
+badarg:
 	ERTS_BIF_PREP_ERROR(ret, BIF_P, BADARG);
     }
     if (deref_de) {
diff --git a/erts/emulator/beam/erl_bif_info.c b/erts/emulator/beam/erl_bif_info.c
index b410578d37..3fb866733c 100644
--- a/erts/emulator/beam/erl_bif_info.c
+++ b/erts/emulator/beam/erl_bif_info.c
@@ -361,8 +361,13 @@ erts_print_system_version(int to, void *arg, Process *c_p)
 }
 
 typedef struct {
+    /* {Entity,Node} = {monitor.Name,monitor.Pid} for external by name
+     * {Entity,Node} = {monitor.Pid,NIL} for external/external by pid
+     * {Entity,Node} = {monitor.Name,erlang:node()} for internal by name */
     Eterm entity;
     Eterm node;
+    /* pid is actual target being monitored, no matter pid/port or name */
+    Eterm pid;
 } MonitorInfo;
 
 typedef struct {
@@ -420,21 +425,27 @@ static void collect_one_origin_monitor(ErtsMonitor *mon, void *vmicp)
     EXTEND_MONITOR_INFOS(micp);
     if (is_atom(mon->pid)) { /* external by name */
 	micp->mi[micp->mi_i].entity = mon->name;
-	micp->mi[micp->mi_i].node = mon->pid;
-	micp->sz += 3; /* need one 2-tuple */
+        micp->mi[micp->mi_i].node = mon->pid;
+        micp->sz += 3; /* need one 2-tuple */
     } else if (is_external_pid(mon->pid)) { /* external by pid */
 	micp->mi[micp->mi_i].entity = mon->pid;
-	micp->mi[micp->mi_i].node = NIL;
-	micp->sz += NC_HEAP_SIZE(mon->pid);
+        micp->mi[micp->mi_i].node = NIL;
+        micp->sz += NC_HEAP_SIZE(mon->pid);
     } else if (!is_nil(mon->name)) { /* internal by name */
 	micp->mi[micp->mi_i].entity = mon->name;
-	micp->mi[micp->mi_i].node = erts_this_dist_entry->sysname;
-	micp->sz += 3; /* need one 2-tuple */
+        micp->mi[micp->mi_i].node = erts_this_dist_entry->sysname;
+        micp->sz += 3; /* need one 2-tuple */
     } else { /* internal by pid */
 	micp->mi[micp->mi_i].entity = mon->pid;
-	micp->mi[micp->mi_i].node = NIL;
+        micp->mi[micp->mi_i].node = NIL;
 	/* no additional heap space needed */
     }
+
+    /* have always pid at hand, to assist with figuring out if its a port or
+     * a process, when we monitored by name and process_info is requested.
+     * See: erl_bif_info.c:process_info_aux section for am_monitors */
+    micp->mi[micp->mi_i].pid = mon->pid;
+
     micp->mi_i++;
     micp->sz += 2 + 3; /* For a cons cell and a 2-tuple */
 }
@@ -1190,37 +1201,49 @@ process_info_aux(Process *BIF_P,
 
     case am_monitors: {
 	MonitorInfoCollection mic;
-	int i;
+        int i;
 
 	INIT_MONITOR_INFOS(mic);
-	erts_doforall_monitors(ERTS_P_MONITORS(rp),&collect_one_origin_monitor,&mic);
-	hp = HAlloc(BIF_P, 3 + mic.sz);
+        erts_doforall_monitors(ERTS_P_MONITORS(rp),
+                               &collect_one_origin_monitor, &mic);
+        hp = HAlloc(BIF_P, 3 + mic.sz);
 	res = NIL;
 	for (i = 0; i < mic.mi_i; i++) {
 	    if (is_atom(mic.mi[i].entity)) {
 		/* Monitor by name. 
-		 * Build {process, {Name, Node}} and cons it. 
+                 * Build {process|port, {Name, Node}} and cons it.
 		 */
 		Eterm t1, t2;
+                /* If pid is an atom, then it is a remote named monitor, which
+                   has to be a process */
+                Eterm m_type = is_port(mic.mi[i].pid) ? am_port : am_process;
+                ASSERT(is_pid(mic.mi[i].pid)
+                    || is_port(mic.mi[i].pid)
+                    || is_atom(mic.mi[i].pid));
 
 		t1 = TUPLE2(hp, mic.mi[i].entity, mic.mi[i].node);
 		hp += 3;
-		t2 = TUPLE2(hp, am_process, t1);
+                t2 = TUPLE2(hp, m_type, t1);
 		hp += 3;
 		res = CONS(hp, t2, res);
-		hp += 2;
+                hp += 2;
 	    }
 	    else {
-		/* Monitor by pid. Build {process, Pid} and cons it. */
+                /* Monitor by pid. Build {process|port, Pid} and cons it. */
 		Eterm t;
 		Eterm pid = STORE_NC(&hp, &MSO(BIF_P), mic.mi[i].entity);
-		t = TUPLE2(hp, am_process, pid);
+
+                Eterm m_type = is_port(mic.mi[i].pid) ? am_port : am_process;
+                ASSERT(is_pid(mic.mi[i].pid)
+                    || is_port(mic.mi[i].pid));
+
+                t = TUPLE2(hp, m_type, pid);
 		hp += 3;
 		res = CONS(hp, t, res);
-		hp += 2;
+                hp += 2;
 	    }
 	}
-	DESTROY_MONITOR_INFOS(mic);
+        DESTROY_MONITOR_INFOS(mic);
 	break;
     }
 
@@ -2880,7 +2903,8 @@ BIF_RETTYPE system_info_1(BIF_ALIST_1)
 */
 
 Eterm
-erts_bld_port_info(Eterm **hpp, ErlOffHeap *ohp, Uint *szp, Port *prt, Eterm item)
+erts_bld_port_info(Eterm **hpp, ErlOffHeap *ohp, Uint *szp, Port *prt,
+                   Eterm item)
 {
     Eterm res = THE_NON_VALUE;
 
@@ -2928,8 +2952,8 @@ erts_bld_port_info(Eterm **hpp, ErlOffHeap *ohp, Uint *szp, Port *prt, Eterm ite
 	Eterm item;
 
 	INIT_MONITOR_INFOS(mic);
-
-	erts_doforall_monitors(ERTS_P_MONITORS(prt), &collect_one_origin_monitor, &mic);
+        erts_doforall_monitors(ERTS_P_MONITORS(prt),
+                               &collect_one_origin_monitor, &mic);
 
 	if (szp)
 	    *szp += mic.sz;
@@ -2938,14 +2962,16 @@ erts_bld_port_info(Eterm **hpp, ErlOffHeap *ohp, Uint *szp, Port *prt, Eterm ite
 	    res = NIL;
 	    for (i = 0; i < mic.mi_i; i++) {
 		Eterm t;
-		item = STORE_NC(hpp, ohp, mic.mi[i].entity);
-		t = TUPLE2(*hpp, am_process, item);
+                Eterm m_type;
+
+                item = STORE_NC(hpp, ohp, mic.mi[i].entity);
+                m_type = is_port(item) ? am_port : am_process;
+                t = TUPLE2(*hpp, m_type, item);
 		*hpp += 3;
 		res = CONS(*hpp, t, res);
 		*hpp += 2;
 	    }
-	}
-
+        } // hpp
 	DESTROY_MONITOR_INFOS(mic);
 
 	if (szp) {
@@ -2953,6 +2979,32 @@ erts_bld_port_info(Eterm **hpp, ErlOffHeap *ohp, Uint *szp, Port *prt, Eterm ite
 	    goto done;
 	}
     }
+    else if (item == am_monitored_by) {
+        MonitorInfoCollection mic;
+        int i;
+        Eterm item;
+
+        INIT_MONITOR_INFOS(mic);
+        erts_doforall_monitors(ERTS_P_MONITORS(prt),
+                               &collect_one_target_monitor, &mic);
+        if (szp)
+            *szp += mic.sz;
+
+        if (hpp) {
+            res = NIL;
+            for (i = 0; i < mic.mi_i; ++i) {
+                item = STORE_NC(hpp, ohp, mic.mi[i].entity);
+                res = CONS(*hpp, item, res);
+                *hpp += 2;
+            }
+        } // hpp
+        DESTROY_MONITOR_INFOS(mic);
+
+        if (szp) {
+            res = am_true;
+            goto done;
+        }
+    }
     else if (item == am_name) {
 	int count = sys_strlen(prt->name);
 
diff --git a/erts/emulator/beam/erl_bif_port.c b/erts/emulator/beam/erl_bif_port.c
index fefa9d8391..90e78a9b0b 100644
--- a/erts/emulator/beam/erl_bif_port.c
+++ b/erts/emulator/beam/erl_bif_port.c
@@ -139,6 +139,12 @@ sig_lookup_port(Process *c_p, Eterm id_or_name)
     return lookup_port(c_p, id_or_name, ERTS_PORT_SFLGS_INVALID_DRIVER_LOOKUP);
 }
 
+/* Non-inline copy of sig_lookup_port to be exported */
+Port *erts_sig_lookup_port(Process *c_p, Eterm id_or_name)
+{
+    return lookup_port(c_p, id_or_name, ERTS_PORT_SFLGS_INVALID_DRIVER_LOOKUP);
+}
+
 static ERTS_INLINE Port *
 data_lookup_port(Process *c_p, Eterm id_or_name)
 {
diff --git a/erts/emulator/beam/erl_port.h b/erts/emulator/beam/erl_port.h
index f0075ca2b9..f90844ccc8 100644
--- a/erts/emulator/beam/erl_port.h
+++ b/erts/emulator/beam/erl_port.h
@@ -361,6 +361,8 @@ Eterm erts_request_io_bytes(Process *c_p);
 #define ERTS_PORT_REDS_CONNECT		(CONTEXT_REDS/200)
 #define ERTS_PORT_REDS_UNLINK		(CONTEXT_REDS/200)
 #define ERTS_PORT_REDS_LINK		(CONTEXT_REDS/200)
+#define ERTS_PORT_REDS_MONITOR		(CONTEXT_REDS/200)
+#define ERTS_PORT_REDS_DEMONITOR	(CONTEXT_REDS/200)
 #define ERTS_PORT_REDS_BADSIG		(CONTEXT_REDS/200)
 #define ERTS_PORT_REDS_CONTROL		(CONTEXT_REDS/100)
 #define ERTS_PORT_REDS_CALL		(CONTEXT_REDS/50)
@@ -850,16 +852,20 @@ void erts_port_resume_procs(Port *);
 
 struct binary;
 
-#define ERTS_P2P_SIG_TYPE_BAD			0
-#define ERTS_P2P_SIG_TYPE_OUTPUT		1
-#define ERTS_P2P_SIG_TYPE_OUTPUTV		2
-#define ERTS_P2P_SIG_TYPE_CONNECT		3
-#define ERTS_P2P_SIG_TYPE_EXIT			4
-#define ERTS_P2P_SIG_TYPE_CONTROL		5
-#define ERTS_P2P_SIG_TYPE_CALL			6
-#define ERTS_P2P_SIG_TYPE_INFO			7
-#define ERTS_P2P_SIG_TYPE_LINK			8
-#define ERTS_P2P_SIG_TYPE_UNLINK		9
+enum {
+    ERTS_P2P_SIG_TYPE_BAD       = 0,
+    ERTS_P2P_SIG_TYPE_OUTPUT    = 1,
+    ERTS_P2P_SIG_TYPE_OUTPUTV   = 2,
+    ERTS_P2P_SIG_TYPE_CONNECT   = 3,
+    ERTS_P2P_SIG_TYPE_EXIT      = 4,
+    ERTS_P2P_SIG_TYPE_CONTROL   = 5,
+    ERTS_P2P_SIG_TYPE_CALL      = 6,
+    ERTS_P2P_SIG_TYPE_INFO      = 7,
+    ERTS_P2P_SIG_TYPE_LINK      = 8,
+    ERTS_P2P_SIG_TYPE_UNLINK    = 9,
+    ERTS_P2P_SIG_TYPE_MONITOR   = 10,
+    ERTS_P2P_SIG_TYPE_DEMONITOR = 11
+};
 
 #define ERTS_P2P_SIG_TYPE_BITS			4
 #define ERTS_P2P_SIG_TYPE_MASK \
@@ -921,6 +927,15 @@ struct ErtsProc2PortSigData_ {
 	struct {
 	    Eterm from;
 	} unlink;
+        struct {
+            Eterm origin;   /* who receives monitor event, pid */
+            Eterm name;     /* either name for named monitor, or port id */
+        } monitor;
+        struct {
+            Eterm origin;   /* who is at the other end of the monitor, pid */
+            Eterm name;     /* port id */
+            Uint32 ref[ERTS_MAX_REF_NUMBERS]; /* box contents of a ref */
+        } demonitor;
     } u;
 } ;
 
@@ -1017,6 +1032,29 @@ ErtsPortOpResult erts_port_control(Process *, Port *, unsigned int, Eterm, Eterm
 ErtsPortOpResult erts_port_call(Process *, Port *, unsigned int, Eterm, Eterm *);
 ErtsPortOpResult erts_port_info(Process *, Port *, Eterm, Eterm *);
 
+/* Creates monitor between Origin and Target. Ref must be initialized to
+ * a reference (ref may be rewritten to be used to serve additionally as a
+ * signal id). Name is atom if user monitors port by name or NIL */
+ErtsPortOpResult erts_port_monitor(Process *origin, Port *target, Eterm name,
+                                   Eterm *ref);
+
+typedef enum {
+    /* Normal demonitor rules apply with locking and reductions bump */
+    ERTS_PORT_DEMONITOR_NORMAL = 1,
+    /* Relaxed demonitor rules when process is about to die, which means that
+     * pid lookup won't work, locks won't work, no reductions bump. */
+    ERTS_PORT_DEMONITOR_ORIGIN_ON_DEATHBED = 2,
+} ErtsDemonitorMode;
+
+/* Removes monitor between origin and target, identified by ref.
+ * origin_is_dying can be 0 (false, normal locking rules and reductions bump
+ * apply) or 1 (true, in case when we avoid origin locking) */
+ErtsPortOpResult erts_port_demonitor(Process *origin, ErtsDemonitorMode mode,
+                                    Port *target, Eterm ref,
+                                    Eterm *trap_ref);
+/* defined in erl_bif_port.c */
+Port *erts_sig_lookup_port(Process *c_p, Eterm id_or_name);
+
 int erts_port_output_async(Port *, Eterm, Eterm);
 
 /*
diff --git a/erts/emulator/beam/erl_process.c b/erts/emulator/beam/erl_process.c
index 5193be85b4..48f89d2bd7 100644
--- a/erts/emulator/beam/erl_process.c
+++ b/erts/emulator/beam/erl_process.c
@@ -12239,7 +12239,6 @@ static void doit_exit_monitor(ErtsMonitor *mon, void *vpcontext)
     ExitMonitorContext *pcontext = vpcontext;
     DistEntry *dep;
     ErtsMonitor *rmon;
-    Process *rp;
 
     switch (mon->type) {
     case MON_ORIGIN:
@@ -12268,9 +12267,10 @@ static void doit_exit_monitor(ErtsMonitor *mon, void *vpcontext)
 		erts_deref_dist_entry(dep);
 	    }
 	} else {
-	    ASSERT(is_pid(mon->pid));
-	    if (is_internal_pid(mon->pid)) { /* local by pid or name */
-		rp = erts_pid2proc(NULL, 0, mon->pid, ERTS_PROC_LOCK_LINK);
+            ASSERT(is_pid(mon->pid) || is_port(mon->pid));
+            /* if is local by pid or name */
+            if (is_internal_pid(mon->pid)) {
+                Process *rp = erts_pid2proc(NULL, 0, mon->pid, ERTS_PROC_LOCK_LINK);
 		if (!rp) {
 		    goto done;
 		}
@@ -12280,7 +12280,17 @@ static void doit_exit_monitor(ErtsMonitor *mon, void *vpcontext)
 		    goto done;
 		}
 		erts_destroy_monitor(rmon);
-	    } else { /* remote by pid */
+            } else if (is_internal_port(mon->pid)) {
+                /* Is a local port */
+                Port *prt = erts_port_lookup_raw(mon->pid);
+                if (!prt) {
+                    goto done;
+                }
+                erts_port_demonitor(pcontext->p,
+                                    ERTS_PORT_DEMONITOR_ORIGIN_ON_DEATHBED,
+                                    prt, mon->ref, NULL);
+                return; /* let erts_port_demonitor do the deletion */
+            } else { /* remote by pid */
 		ASSERT(is_external_pid(mon->pid));
 		dep = external_pid_dist_entry(mon->pid);
 		ASSERT(dep != NULL);
@@ -12318,6 +12328,7 @@ static void doit_exit_monitor(ErtsMonitor *mon, void *vpcontext)
 	    erts_port_release(prt); 
 	} else if (is_internal_pid(mon->pid)) {/* local by name or pid */
 	    Eterm watched;
+            Process *rp;
 	    DeclareTmpHeapNoproc(lhp,3);
 	    ErtsProcLocks rp_locks = (ERTS_PROC_LOCK_LINK
 				      | ERTS_PROC_LOCKS_MSG_SEND);
diff --git a/erts/emulator/beam/io.c b/erts/emulator/beam/io.c
index 01df5476db..cb8792dffa 100644
--- a/erts/emulator/beam/io.c
+++ b/erts/emulator/beam/io.c
@@ -1260,7 +1260,7 @@ typedef struct {
 /*
  * Try doing an immediate driver callback call from a process. If
  * this fail, the operation should be scheduled in the normal case...
- *
+ * Returns: ok to do the call, or error (lock busy, does not exist, etc)
  */
 static ERTS_INLINE ErtsTryImmDrvCallResult
 try_imm_drv_call(ErtsTryImmDrvCallState *sp)
@@ -3074,6 +3074,250 @@ erts_port_link(Process *c_p, Port *prt, Eterm to, Eterm *refp)
 }
 
 static void
+port_monitor_failure(Eterm port_id, Eterm origin, Eterm ref_DOWN)
+{
+    Process       *origin_p;
+    ErtsProcLocks p_locks = ERTS_PROC_LOCK_LINK;
+    ASSERT(is_internal_pid(origin));
+
+    origin_p = erts_pid2proc(NULL, 0, origin, p_locks);
+    if (! origin_p) { return; }
+
+    /* Send the DOWN message immediately. Ref is made on the fly because
+     * caller has never seen it yet. */
+    erts_queue_monitor_message(origin_p, &p_locks, ref_DOWN,
+                               am_port, port_id, am_noproc);
+    erts_smp_proc_unlock(origin_p, p_locks);
+}
+
+/* Origin wants to monitor port Prt. State contains possible error, which has
+ * happened just before. Name is either NIL or an atom, if user monitors
+ * a port by name. Ref is premade reference that will be returned to user */
+static void
+port_monitor(Port *prt, erts_aint32_t state, Eterm origin,
+             Eterm name, Eterm ref)
+{
+    Eterm name_or_nil = is_atom(name) ? name : NIL;
+
+    ASSERT(is_pid(origin));
+    ASSERT(is_atom(name) || is_port(name) || name == NIL);
+    ASSERT(is_internal_ref(ref));
+
+    if (!(state & ERTS_PORT_SFLGS_INVALID_LOOKUP)) {
+        ErtsProcLocks p_locks = ERTS_PROC_LOCK_LINK;
+
+        Process *origin_p = erts_pid2proc(NULL, 0, origin, p_locks);
+        if (! origin_p) {
+            goto failure;
+        }
+        erts_add_monitor(&ERTS_P_MONITORS(origin_p), MON_ORIGIN, ref,
+                         prt->common.id, name_or_nil);
+        erts_add_monitor(&ERTS_P_MONITORS(prt), MON_TARGET, ref,
+                         origin, name_or_nil);
+
+        erts_smp_proc_unlock(origin_p, p_locks);
+    } else {
+failure:
+        port_monitor_failure(prt->common.id, origin, ref);
+    }
+}
+
+static int
+port_sig_monitor(Port *prt, erts_aint32_t state, int op,
+                 ErtsProc2PortSigData *sigdp)
+{
+    Eterm hp[REF_THING_SIZE];
+    Eterm ref = make_internal_ref(&hp);
+    write_ref_thing(hp, sigdp->ref[0], sigdp->ref[1], sigdp->ref[2]);
+
+    if (op == ERTS_PROC2PORT_SIG_EXEC) {
+        /* erts_add_monitor call inside port_monitor will copy ref from hp */
+        port_monitor(prt, state,
+                     sigdp->u.monitor.origin,
+                     sigdp->u.monitor.name,
+                     ref);
+    } else {
+        port_monitor_failure(sigdp->u.monitor.name,
+                             sigdp->u.monitor.origin,
+                             ref);
+    }
+    if (sigdp->flags & ERTS_P2P_SIG_DATA_FLG_REPLY) {
+        port_sched_op_reply(sigdp->caller, sigdp->ref, am_true, prt);
+    }
+    return ERTS_PORT_REDS_MONITOR;
+}
+
+/* Creates monitor between Origin and Target. Ref must be initialized to
+ * a reference (ref may be rewritten to be used to serve additionally as a
+ * signal id). Name is atom if user monitors port by name or NIL */
+ErtsPortOpResult
+erts_port_monitor(Process *origin, Port *port, Eterm name, Eterm *refp)
+{
+    ErtsProc2PortSigData *sigdp;
+    ErtsTryImmDrvCallState try_call_state
+        = ERTS_INIT_TRY_IMM_DRV_CALL_STATE(
+                origin, port, ERTS_PORT_SFLGS_INVALID_LOOKUP,
+                0,
+                0, /* trap_ref is always set so !trap_ref always is false */
+                am_monitor);
+
+    ASSERT(origin);
+    ASSERT(port);
+    ASSERT(is_atom(name) || is_port(name));
+    ASSERT(refp);
+
+    switch (try_imm_drv_call(&try_call_state)) {
+    case ERTS_TRY_IMM_DRV_CALL_OK:
+        port_monitor(port, try_call_state.state, origin->common.id, name, *refp);
+        finalize_imm_drv_call(&try_call_state);
+        BUMP_REDS(origin, ERTS_PORT_REDS_MONITOR);
+        return ERTS_PORT_OP_DONE;
+    case ERTS_TRY_IMM_DRV_CALL_INVALID_PORT:
+        return ERTS_PORT_OP_BADARG;
+    default:
+        break; /* Schedule call instead... */
+    }
+
+    sigdp = erts_port_task_alloc_p2p_sig_data();
+    sigdp->flags = ERTS_P2P_SIG_TYPE_MONITOR;
+    sigdp->u.monitor.origin = origin->common.id;
+    sigdp->u.monitor.name   = name; /* either named monitor, or port id */
+
+    /* Ref contents will be initialized here */
+    return erts_schedule_proc2port_signal(origin, port, origin->common.id,
+                                          refp, sigdp, 0, NULL,
+                                          port_sig_monitor);
+}
+
+static void
+port_demonitor_failure(Eterm port_id, Eterm origin, Eterm ref)
+{
+    Process       *origin_p;
+    ErtsProcLocks rp_locks = ERTS_PROC_LOCK_LINK;
+    ErtsMonitor   *mon1;
+    ASSERT(is_internal_pid(origin));
+
+    origin_p = erts_pid2proc(NULL, 0, origin, rp_locks);
+    if (! origin_p) { return; }
+
+    /* do not send any DOWN messages, drop monitors on process */
+    mon1 = erts_remove_monitor(&ERTS_P_MONITORS(origin_p), ref);
+    if (mon1 != NULL) {
+        erts_destroy_monitor(mon1);
+    }
+
+    erts_smp_proc_unlock(origin_p, rp_locks);
+}
+
+/* Origin wants to demonitor port Prt. State contains possible error, which has
+ * happened just before. Ref is reference to monitor */
+static void
+port_demonitor(Port *port, erts_aint32_t state, Eterm origin, Eterm ref)
+{
+    ASSERT(port);
+    ASSERT(is_pid(origin));
+    ASSERT(is_internal_ref(ref));
+
+    if (!(state & ERTS_PORT_SFLGS_INVALID_LOOKUP)) {
+        ErtsProcLocks p_locks = ERTS_PROC_LOCK_LINK;
+        Process *origin_p = erts_pid2proc(NULL, 0, origin, p_locks);
+        if (origin_p) {
+            ErtsMonitor *mon1 = erts_remove_monitor(&ERTS_P_MONITORS(origin_p),
+                                                    ref);
+            if (mon1 != NULL) {
+                erts_destroy_monitor(mon1);
+            }
+        }
+        if (1) {
+            ErtsMonitor *mon2 = erts_remove_monitor(&ERTS_P_MONITORS(port),
+                                                    ref);
+            if (mon2 != NULL) {
+                erts_destroy_monitor(mon2);
+            }
+        }
+        if (origin_p) { /* when origin is dying, it won't be found */
+            erts_smp_proc_unlock(origin_p, p_locks);
+        }
+    } else {
+        port_demonitor_failure(port->common.id, origin, ref);
+    }
+}
+
+static int
+port_sig_demonitor(Port *prt, erts_aint32_t state, int op,
+                   ErtsProc2PortSigData *sigdp)
+{
+    Eterm hp[REF_THING_SIZE];
+    Eterm ref = make_internal_ref(&hp);
+    write_ref_thing(hp, sigdp->u.demonitor.ref[0],
+                    sigdp->u.demonitor.ref[1],
+                    sigdp->u.demonitor.ref[2]);
+    if (op == ERTS_PROC2PORT_SIG_EXEC) {
+        port_demonitor(prt, state, sigdp->u.demonitor.origin, ref);
+    } else {
+        port_demonitor_failure(sigdp->u.demonitor.name,
+                               sigdp->u.demonitor.origin,
+                               ref);
+    }
+    if (sigdp->flags & ERTS_P2P_SIG_DATA_FLG_REPLY) {
+        port_sched_op_reply(sigdp->caller, sigdp->ref, am_true, prt);
+    }
+    return ERTS_PORT_REDS_DEMONITOR;
+}
+
+/* Removes monitor between origin and target, identified by ref.
+ * Mode defines normal or relaxed demonitor rules (process is at death) */
+ErtsPortOpResult erts_port_demonitor(Process *origin, ErtsDemonitorMode mode,
+                                     Port *target, Eterm ref,
+                                     Eterm *trap_ref)
+{
+    Process *c_p = mode == ERTS_PORT_DEMONITOR_NORMAL ? origin : NULL;
+    ErtsProc2PortSigData *sigdp;
+    ErtsTryImmDrvCallState try_call_state
+        = ERTS_INIT_TRY_IMM_DRV_CALL_STATE(
+                c_p,
+                target, ERTS_PORT_SFLGS_INVALID_LOOKUP,
+                0,
+                !trap_ref,
+                am_demonitor);
+
+    ASSERT(origin);
+    ASSERT(target);
+    ASSERT(is_internal_ref(ref));
+
+    switch (try_imm_drv_call(&try_call_state)) {
+    case ERTS_TRY_IMM_DRV_CALL_OK:
+        port_demonitor(target, try_call_state.state, origin->common.id, ref);
+        finalize_imm_drv_call(&try_call_state);
+        if (mode == ERTS_PORT_DEMONITOR_NORMAL) {
+            BUMP_REDS(origin, ERTS_PORT_REDS_DEMONITOR);
+        }
+        return ERTS_PORT_OP_DONE;
+    case ERTS_TRY_IMM_DRV_CALL_INVALID_PORT:
+        return ERTS_PORT_OP_BADARG;
+    default:
+        break; /* Schedule call instead... */
+    }
+
+    sigdp = erts_port_task_alloc_p2p_sig_data();
+    sigdp->flags = ERTS_P2P_SIG_TYPE_DEMONITOR;
+    sigdp->u.demonitor.origin = origin->common.id;
+    sigdp->u.demonitor.name = target->common.id;
+    {
+        RefThing *reft = ref_thing_ptr(ref);
+        /* Start from 1 skip ref arity */
+        sys_memcpy(sigdp->u.demonitor.ref,
+                   internal_thing_ref_numbers(reft),
+                   sizeof(sigdp->u.demonitor.ref));
+    }
+
+    /* Ref contents will be initialized here */
+    return erts_schedule_proc2port_signal(c_p, target, origin->common.id,
+                                          trap_ref, sigdp, 0, NULL,
+                                          port_sig_demonitor);
+}
+
+static void
 init_ack_send_reply(Port *port, Eterm resp)
 {
 
@@ -3942,23 +4186,30 @@ erts_terminate_port(Port *pp)
     terminate_port(pp);
 }
 
+static void port_fire_one_monitor(ErtsMonitor *mon, void *ctx0);
 static void sweep_one_monitor(ErtsMonitor *mon, void *vpsc)
 {
-    ErtsMonitor *rmon;
-    Process *rp;
+    switch (mon->type) {
+    case MON_ORIGIN: {
+        ErtsMonitor *rmon;
+        Process *rp;
 
-    ASSERT(mon->type == MON_ORIGIN);
-    ASSERT(is_internal_pid(mon->pid));
-    rp = erts_pid2proc(NULL, 0, mon->pid, ERTS_PROC_LOCK_LINK);
-    if (!rp) {
-	goto done;
-    }
-    rmon = erts_remove_monitor(&ERTS_P_MONITORS(rp), mon->ref);
-    erts_smp_proc_unlock(rp, ERTS_PROC_LOCK_LINK);
-    if (rmon == NULL) {
-	goto done;
+        ASSERT(is_internal_pid(mon->pid));
+        rp = erts_pid2proc(NULL, 0, mon->pid, ERTS_PROC_LOCK_LINK);
+        if (!rp) {
+            goto done;
+        }
+        rmon = erts_remove_monitor(&ERTS_P_MONITORS(rp), mon->ref);
+        erts_smp_proc_unlock(rp, ERTS_PROC_LOCK_LINK);
+        if (rmon == NULL) {
+            goto done;
+        }
+        erts_destroy_monitor(rmon);
+    } break;
+    case MON_TARGET: {
+        port_fire_one_monitor(mon, vpsc); /* forward call */
+    } break;
     }
-    erts_destroy_monitor(rmon);
  done:
     erts_destroy_monitor(mon);
 }
@@ -4039,6 +4290,43 @@ static void sweep_one_link(ErtsLink *lnk, void *vpsc)
     erts_destroy_link(lnk);
 }
 
+static void
+port_fire_one_monitor(ErtsMonitor *mon, void *ctx0)
+{
+    Process      *origin;
+    ErtsProcLocks origin_locks;
+
+    if (mon->type != MON_TARGET || ! is_pid(mon->pid)) {
+        return;
+    }
+    /*
+     * Proceed here if someone monitors us, we (port) are the target and
+     * origin is some process
+     */
+    origin_locks = ERTS_PROC_LOCKS_MSG_SEND | ERTS_PROC_LOCK_LINK;
+
+    origin = erts_pid2proc(NULL, 0, mon->pid, origin_locks);
+    if (origin) {
+        DeclareTmpHeapNoproc(lhp,3);
+        SweepContext    *ctx = (SweepContext *)ctx0;
+        ErtsMonitor     *rmon;
+        Eterm           watched = (is_atom(mon->name)
+                       ? TUPLE2(lhp, mon->name, erts_this_dist_entry->sysname)
+                       : ctx->port->common.id);
+
+        erts_queue_monitor_message(origin, &origin_locks, mon->ref, am_port,
+                                   watched, ctx->reason);
+        UnUseTmpHeapNoproc(3);
+
+        rmon = erts_remove_monitor(&ERTS_P_MONITORS(origin), mon->ref);
+        erts_smp_proc_unlock(origin, origin_locks);
+
+        if (rmon) {
+            erts_destroy_monitor(rmon);
+        }
+    }
+}
+
 /* 'from' is sending 'this_port' an exit signal, (this_port must be internal).
  * If reason is normal we don't do anything, *unless* from is our connected
  * process in which case we close the port. Any other reason kills the port.
@@ -4050,39 +4338,40 @@ static void sweep_one_link(ErtsLink *lnk, void *vpsc)
  */
 
 int
-erts_deliver_port_exit(Port *p, Eterm from, Eterm reason, int send_closed,
+erts_deliver_port_exit(Port *prt, Eterm from, Eterm reason, int send_closed,
                        int drop_normal)
 {
    ErtsLink *lnk;
-   Eterm rreason;
+   Eterm modified_reason;
    erts_aint32_t state, set_state_flags;
 
    ERTS_SMP_CHK_NO_PROC_LOCKS;
-   ERTS_SMP_LC_ASSERT(erts_lc_is_port_locked(p));
+   ERTS_SMP_LC_ASSERT(erts_lc_is_port_locked(prt));
 
-   rreason = (reason == am_kill) ? am_killed : reason;
+   modified_reason = (reason == am_kill) ? am_killed : reason;
 
 #ifdef USE_VM_PROBES
    if (DTRACE_ENABLED(port_exit)) {
        DTRACE_CHARBUF(from_str, DTRACE_TERM_BUF_SIZE);
        DTRACE_CHARBUF(port_str, DTRACE_TERM_BUF_SIZE);
-       DTRACE_CHARBUF(rreason_str, 64);
+       DTRACE_CHARBUF(reason_str, 64);
 
        erts_snprintf(from_str, sizeof(DTRACE_CHARBUF_NAME(from_str)), "%T", from);
-       dtrace_port_str(p, port_str);
-       erts_snprintf(rreason_str, sizeof(DTRACE_CHARBUF_NAME(rreason_str)), "%T", rreason);
-       DTRACE4(port_exit, from_str, port_str, p->name, rreason_str);
+       dtrace_port_str(prt, port_str);
+       erts_snprintf(reason_str, sizeof(DTRACE_CHARBUF_NAME(reason_str)), "%T",
+                     modified_reason);
+       DTRACE4(port_exit, from_str, port_str, prt->name, reason_str);
    }
 #endif
 
-   state = erts_atomic32_read_nob(&p->state);
+   state = erts_atomic32_read_nob(&prt->state);
    if (state & (ERTS_PORT_SFLGS_DEAD
 		| ERTS_PORT_SFLG_EXITING
 		| ERTS_PORT_SFLG_CLOSING))
        return 0;
 
-   if (reason == am_normal && from != ERTS_PORT_GET_CONNECTED(p)
-       && from != p->common.id && drop_normal) {
+   if (reason == am_normal && from != ERTS_PORT_GET_CONNECTED(prt)
+       && from != prt->common.id && drop_normal) {
        return 0;
    }
 
@@ -4090,53 +4379,54 @@ erts_deliver_port_exit(Port *p, Eterm from, Eterm reason, int send_closed,
    if (send_closed)
        set_state_flags |= ERTS_PORT_SFLG_SEND_CLOSED;
 
-   erts_port_task_sched_enter_exiting_state(&p->sched);
+   erts_port_task_sched_enter_exiting_state(&prt->sched);
    
-   state = erts_atomic32_read_bor_mb(&p->state, set_state_flags);
+   state = erts_atomic32_read_bor_mb(&prt->state, set_state_flags);
    state |= set_state_flags;
 
-   if (IS_TRACED_FL(p, F_TRACE_PORTS))
-   	trace_port(p, am_closed, reason);
+   if (IS_TRACED_FL(prt, F_TRACE_PORTS))
+        trace_port(prt, am_closed, reason);
 
-   erts_trace_check_exiting(p->common.id);
+   erts_trace_check_exiting(prt->common.id);
 
-   set_busy_port(ERTS_Port2ErlDrvPort(p), 0);
+   set_busy_port(ERTS_Port2ErlDrvPort(prt), 0);
 
-   if (p->common.u.alive.reg != NULL)
-       (void) erts_unregister_name(NULL, 0, p, p->common.u.alive.reg->name);
+   if (prt->common.u.alive.reg != NULL)
+       (void) erts_unregister_name(NULL, 0, prt, prt->common.u.alive.reg->name);
 
    {
-       SweepContext sc = {p, rreason};
-       lnk = ERTS_P_LINKS(p);
-       ERTS_P_LINKS(p) = NULL;
+       SweepContext sc = {prt, modified_reason};
+       lnk = ERTS_P_LINKS(prt);
+       ERTS_P_LINKS(prt) = NULL;
        erts_sweep_links(lnk, &sweep_one_link, &sc);
    }
-   DRV_MONITOR_LOCK_PDL(p);
+   DRV_MONITOR_LOCK_PDL(prt);
    {
-       ErtsMonitor *moni = ERTS_P_MONITORS(p);
-       ERTS_P_MONITORS(p) = NULL;
-       erts_sweep_monitors(moni, &sweep_one_monitor, NULL);
+       SweepContext ctx = {prt, modified_reason};
+       ErtsMonitor *moni = ERTS_P_MONITORS(prt);
+       ERTS_P_MONITORS(prt) = NULL;
+       erts_sweep_monitors(moni, &sweep_one_monitor, &ctx);
    } 
-   DRV_MONITOR_UNLOCK_PDL(p);
+   DRV_MONITOR_UNLOCK_PDL(prt);
 
-   if ((state & ERTS_PORT_SFLG_DISTRIBUTION) && p->dist_entry) {
-       erts_do_net_exits(p->dist_entry, rreason);
-       erts_deref_dist_entry(p->dist_entry); 
-       p->dist_entry = NULL;
-       erts_atomic32_read_band_relb(&p->state,
+   if ((state & ERTS_PORT_SFLG_DISTRIBUTION) && prt->dist_entry) {
+       erts_do_net_exits(prt->dist_entry, modified_reason);
+       erts_deref_dist_entry(prt->dist_entry);
+       prt->dist_entry = NULL;
+       erts_atomic32_read_band_relb(&prt->state,
 				    ~ERTS_PORT_SFLG_DISTRIBUTION);
    }
        
-   if ((reason != am_kill) && !is_port_ioq_empty(p)) {
+   if ((reason != am_kill) && !is_port_ioq_empty(prt)) {
        /* must turn exiting flag off */
-       erts_atomic32_read_bset_relb(&p->state,
+       erts_atomic32_read_bset_relb(&prt->state,
 				    (ERTS_PORT_SFLG_EXITING
 				     | ERTS_PORT_SFLG_CLOSING),
 				    ERTS_PORT_SFLG_CLOSING);
-      flush_port(p);
+      flush_port(prt);
    }
    else {
-       terminate_port(p);
+       terminate_port(prt);
    }
 
    return 1;
diff --git a/erts/emulator/beam/register.c b/erts/emulator/beam/register.c
index 77f79fcea4..ac7096745e 100644
--- a/erts/emulator/beam/register.c
+++ b/erts/emulator/beam/register.c
@@ -323,7 +323,8 @@ erts_whereis_name(Process *c_p,
 		  Process** proc,
 		  ErtsProcLocks need_locks,
 		  int flags,
-		  Port** port)
+		  Port** port,
+                  int lock_port)
 {
     RegProc* rp = NULL;
     HashValue hval;
@@ -406,31 +407,33 @@ erts_whereis_name(Process *c_p,
 	    *port = NULL;
 	else {
 #ifdef ERTS_SMP
-	    if (pending_port == rp->pt)
-		pending_port = NULL;
-	    else {
-		if (pending_port) {
-		    /* Ahh! Registered port changed while reg lock
-		       was unlocked... */
-		    erts_port_release(pending_port);
-		    pending_port = NULL;
-		}
+            if (lock_port) {
+                if (pending_port == rp->pt)
+                    pending_port = NULL;
+                else {
+                    if (pending_port) {
+                        /* Ahh! Registered port changed while reg lock
+                           was unlocked... */
+                        erts_port_release(pending_port);
+                        pending_port = NULL;
+                    }
 		    
-		if (erts_smp_port_trylock(rp->pt) == EBUSY) {
-		    Eterm id = rp->pt->common.id; /* id read only... */
-		    /* Unlock all locks, acquire port lock, and restart... */
-		    if (current_c_p_locks) {
-			erts_smp_proc_unlock(c_p, current_c_p_locks);
-			current_c_p_locks = 0;
-		    }
-		    reg_read_unlock();
-		    pending_port = erts_id2port(id);
-		    goto restart;
-		}
-	    }
+                    if (erts_smp_port_trylock(rp->pt) == EBUSY) {
+                        Eterm id = rp->pt->common.id; /* id read only... */
+                        /* Unlock all locks, acquire port lock, and restart... */
+                        if (current_c_p_locks) {
+                            erts_smp_proc_unlock(c_p, current_c_p_locks);
+                            current_c_p_locks = 0;
+                        }
+                        reg_read_unlock();
+                        pending_port = erts_id2port(id);
+                        goto restart;
+                    }
+                }
+                ERTS_SMP_LC_ASSERT(erts_lc_is_port_locked(rp->pt));
+            }
 #endif
 	    *port = rp->pt;
-	    ERTS_SMP_LC_ASSERT(erts_lc_is_port_locked(*port));
 	}
     }
 
@@ -452,7 +455,7 @@ erts_whereis_process(Process *c_p,
 		     int flags)
 {
     Process *proc;
-    erts_whereis_name(c_p, c_p_locks, name, &proc, need_locks, flags, NULL);
+    erts_whereis_name(c_p, c_p_locks, name, &proc, need_locks, flags, NULL, 0);
     return proc;
 }
 
diff --git a/erts/emulator/beam/register.h b/erts/emulator/beam/register.h
index 88ab7b7bf1..d839f55d6b 100644
--- a/erts/emulator/beam/register.h
+++ b/erts/emulator/beam/register.h
@@ -49,7 +49,7 @@ int erts_register_name(Process *, Eterm, Eterm);
 Eterm erts_whereis_name_to_id(Process *, Eterm);
 void erts_whereis_name(Process *, ErtsProcLocks,
 		       Eterm, Process**, ErtsProcLocks, int,
-		       Port**);
+		       Port**, int);
 Process *erts_whereis_process(Process *,
 			      ErtsProcLocks,
 			      Eterm,
diff --git a/erts/emulator/test/monitor_SUITE.erl b/erts/emulator/test/monitor_SUITE.erl
index 8955e62df5..90d2bd8c5d 100644
--- a/erts/emulator/test/monitor_SUITE.erl
+++ b/erts/emulator/test/monitor_SUITE.erl
@@ -21,6 +21,7 @@
 -module(monitor_SUITE).
 
 -include_lib("common_test/include/ct.hrl").
+-include_lib("eunit/include/eunit.hrl").
 
 -export([all/0, suite/0, groups/0,
          case_1/1, case_1a/1, case_2/1, case_2a/1, mon_e_1/1, demon_e_1/1, demon_1/1,
@@ -706,7 +707,7 @@ named_down(Config) when is_list(Config) ->
     spawn_opt(fun () ->
                       WFun = fun
                                  (F, hej) -> F(F, hopp);
-(F, hopp) -> F(F, hej)
+                                 (F, hopp) -> F(F, hej)
                              end,
                       NoSchedulers = erlang:system_info(schedulers_online),
                       lists:foreach(fun (_) ->
@@ -726,13 +727,14 @@ named_down(Config) when is_list(Config) ->
     NamedProc = spawn_link(fun () ->
                                    receive after infinity -> ok end
                            end),
-    true = register(Name, NamedProc),
+    ?assertEqual(true, register(Name, NamedProc)),
     unlink(NamedProc),
     exit(NamedProc, bang),
     Mon = erlang:monitor(process, Name),
-    receive {'DOWN',Mon, _, _, _} -> ok end,
-    true = register(Name, self()),
-    true = unregister(Name),
+    receive {'DOWN',Mon, _, _, bang} -> ok
+    after 3000 -> ?assert(false) end,
+    ?assertEqual(true, register(Name, self())),
+    ?assertEqual(true, unregister(Name)),
     process_flag(priority,Prio),
     ok.
 
diff --git a/erts/emulator/test/port_SUITE.erl b/erts/emulator/test/port_SUITE.erl
index 79abcbde5f..ee07699884 100644
--- a/erts/emulator/test/port_SUITE.erl
+++ b/erts/emulator/test/port_SUITE.erl
@@ -74,27 +74,68 @@
 %%
 
 
--export([all/0, suite/0, groups/0,
-         init_per_testcase/2, end_per_testcase/2,
-         init_per_suite/1, end_per_suite/1,
-         stream_small/1, stream_big/1,
-         basic_ping/1, slow_writes/1, bad_packet/1, bad_port_messages/1,
-         mul_basic/1, mul_slow_writes/1,
-         dying_port/1, port_program_with_path/1,
-         open_input_file_port/1, open_output_file_port/1,
-         count_fds/1,
-         iter_max_ports/1, eof/1, input_only/1, output_only/1,
-         name1/1,
-         t_binary/1, parallell/1, t_exit/1,
-         env/1, huge_env/1, bad_env/1, cd/1, exit_status/1,
-	 bad_args/1,
-         tps_16_bytes/1, tps_1K/1, line/1, stderr_to_stdout/1,
-         otp_3906/1, otp_4389/1, win_massive/1, win_massive_client/1,
-         mix_up_ports/1, otp_5112/1, otp_5119/1, otp_6224/1,
-         exit_status_multi_scheduling_block/1, ports/1,
-         spawn_driver/1, spawn_executable/1, close_deaf_port/1,
-         port_setget_data/1,
-         unregister_name/1, parallelism_option/1]).
+-export([all/0, suite/0, groups/0, init_per_testcase/2, end_per_testcase/2,
+         init_per_suite/1, end_per_suite/1]).
+-export([
+    bad_args/1,
+    bad_env/1,
+    bad_packet/1,
+    bad_port_messages/1,
+    basic_ping/1,
+    cd/1,
+    close_deaf_port/1,
+    count_fds/1,
+    dying_port/1,
+    env/1,
+    eof/1,
+    exit_status/1,
+    exit_status_multi_scheduling_block/1,
+    huge_env/1,
+    input_only/1,
+    iter_max_ports/1,
+    line/1,
+    mix_up_ports/1,
+    mon_port_invalid_type/1,
+    mon_port_bad_named/1,
+    mon_port_bad_remote_on_local/1,
+    mon_port_local/1,
+    mon_port_name_demonitor/1,
+    mon_port_named/1,
+    mon_port_origin_dies/1,
+    mon_port_pid_demonitor/1,
+    mon_port_remote_on_remote/1,
+    mon_port_driver_die/1,
+    mon_port_driver_die_demonitor/1,
+    mul_basic/1,
+    mul_slow_writes/1,
+    name1/1,
+    open_input_file_port/1,
+    open_output_file_port/1,
+    otp_3906/1,
+    otp_4389/1,
+    otp_5112/1,
+    otp_5119/1,
+    otp_6224/1,
+    output_only/1,
+    parallelism_option/1,
+    parallell/1,
+    port_program_with_path/1,
+    port_setget_data/1,
+    ports/1,
+    slow_writes/1,
+    spawn_driver/1,
+    spawn_executable/1,
+    stderr_to_stdout/1,
+    stream_big/1,
+    stream_small/1,
+    t_binary/1,
+    t_exit/1,
+    tps_16_bytes/1,
+    tps_1K/1,
+    unregister_name/1,
+    win_massive/1,
+    win_massive_client/1
+]).
 
 -export([do_iter_max_ports/2]).
 
@@ -105,12 +146,13 @@
 
 -include_lib("common_test/include/ct.hrl").
 -include_lib("kernel/include/file.hrl").
+-include_lib("eunit/include/eunit.hrl").
 
 suite() ->
     [{ct_hooks,[ts_install_cth]},
      {timetrap, {seconds, 10}}].
 
-all() -> 
+all() ->
     [otp_6224, {group, stream}, basic_ping, slow_writes,
      bad_packet, bad_port_messages, {group, options},
      {group, multiple_packets}, parallell, dying_port,
@@ -123,14 +165,32 @@ all() ->
      exit_status_multi_scheduling_block, ports, spawn_driver,
      spawn_executable, close_deaf_port, unregister_name,
      port_setget_data,
-     parallelism_option].
-
-groups() -> 
+     parallelism_option,
+     mon_port_invalid_type,
+     mon_port_local,
+     mon_port_remote_on_remote,
+     mon_port_bad_remote_on_local,
+     mon_port_origin_dies,
+     mon_port_named,
+     mon_port_bad_named,
+     mon_port_pid_demonitor,
+     mon_port_name_demonitor,
+     mon_port_driver_die,
+     mon_port_driver_die_demonitor
+    ].
+
+groups() ->
     [{stream, [], [stream_small, stream_big]},
      {options, [], [t_binary, eof, input_only, output_only]},
      {multiple_packets, [], [mul_basic, mul_slow_writes]},
      {tps, [], [tps_16_bytes, tps_1K]}].
 
+init_per_testcase(Case, Config) when Case =:= mon_port_driver_die;
+                                     Case =:= mon_port_driver_die_demonitor ->
+    case erlang:system_info(schedulers_online) of
+        1 -> {skip, "Need 2 schedulers to run testcase"};
+        _ -> Config
+    end;
 init_per_testcase(Case, Config) ->
     [{testcase, Case} |Config].
 
@@ -160,7 +220,7 @@ do_win_massive() ->
     ct:timetrap({minutes, 6}),
     SuiteDir = filename:dirname(code:which(?MODULE)),
     Ports = " +Q 8192",
-    {ok, Node} = 
+    {ok, Node} =
     test_server:start_node(win_massive,
                            slave,
                            [{args, " -pa " ++ SuiteDir ++ Ports}]),
@@ -169,7 +229,7 @@ do_win_massive() ->
     ok.
 
 win_massive_client(N) ->
-    {ok,P}=gen_tcp:listen(?WIN_MASSIVE_PORT,[{reuseaddr,true}]), 
+    {ok,P}=gen_tcp:listen(?WIN_MASSIVE_PORT,[{reuseaddr,true}]),
     L = win_massive_loop(P,N),
     Len = length(L),
     lists:foreach(fun(E) ->
@@ -278,7 +338,7 @@ bad_port_messages(Config) when is_list(Config) ->
     bad_message(PortTest, {self(),{connect,no_pid}}),
     ok.
 
-bad_message(PortTest, Message) ->    
+bad_message(PortTest, Message) ->
     P = open_port({spawn,PortTest}, []),
     P ! Message,
     receive
@@ -773,7 +833,7 @@ line(Config) when is_list(Config) ->
     S1 = lists:flatten(io_lib:format("-l~w", [length(L1)])),
     io:format("S1 = ~w, L1 = ~w~n", [S1,L1]),
     port_expect(Config,[{L1,
-                         [{eol, Packet1}, {noeol, Packet2}, eof]}], 0, 
+                         [{eol, Packet1}, {noeol, Packet2}, eof]}], 0,
                 S1, [{line,Siz},eof]),
     %% Test that lonely <CR> Don't get treated as newlines
     port_expect(Config,[{lists:append([Packet1, [13], Packet2,
@@ -844,9 +904,9 @@ env(Config)  when is_list(Config) ->
                      {"glurf","a glorfy string"}]),
 
     %% A lot of non existing variables (mingled with existing)
-    NotExistingList = [{lists:flatten(io_lib:format("V~p_not_existing",[X])),false} 
+    NotExistingList = [{lists:flatten(io_lib:format("V~p_not_existing",[X])),false}
                        ||  X <- lists:seq(1,150)],
-    ExistingList = [{lists:flatten(io_lib:format("V~p_existing",[X])),"a_value"} 
+    ExistingList = [{lists:flatten(io_lib:format("V~p_existing",[X])),"a_value"}
                     ||  X <- lists:seq(1,150)],
     env_slave(Temp, lists:sort(ExistingList ++ NotExistingList)),
     ok.
@@ -1320,22 +1380,22 @@ spawn_driver(Config) when is_list(Config) ->
     ok = load_driver(Path, "echo_drv"),
     Port = erlang:open_port({spawn_driver, "echo_drv"}, []),
     Port ! {self(), {command, "Hello port!"}},
-    receive 
-        {Port, {data, "Hello port!"}} = Msg1 -> 
+    receive
+        {Port, {data, "Hello port!"}} = Msg1 ->
             io:format("~p~n", [Msg1]),
-            ok; 
+            ok;
         Other ->
             ct:fail({unexpected, Other})
     end,
     Port ! {self(), close},
     receive {Port, closed} -> ok end,
 
-    Port2 = erlang:open_port({spawn_driver, "echo_drv -Hello port?"}, 
+    Port2 = erlang:open_port({spawn_driver, "echo_drv -Hello port?"},
                              []),
-    receive 
-        {Port2, {data, "Hello port?"}} = Msg2 -> 
+    receive
+        {Port2, {data, "Hello port?"}} = Msg2 ->
             io:format("~p~n", [Msg2]),
-            ok; 
+            ok;
         Other2 ->
             ct:fail({unexpected2, Other2})
     end,
@@ -1354,23 +1414,23 @@ parallelism_option(Config) when is_list(Config) ->
                             [{parallelism, true}]),
     {parallelism, true} = erlang:port_info(Port, parallelism),
     Port ! {self(), {command, "Hello port!"}},
-    receive 
-        {Port, {data, "Hello port!"}} = Msg1 -> 
+    receive
+        {Port, {data, "Hello port!"}} = Msg1 ->
             io:format("~p~n", [Msg1]),
-            ok; 
+            ok;
         Other ->
             ct:fail({unexpected, Other})
     end,
     Port ! {self(), close},
     receive {Port, closed} -> ok end,
 
-    Port2 = erlang:open_port({spawn_driver, "echo_drv -Hello port?"}, 
+    Port2 = erlang:open_port({spawn_driver, "echo_drv -Hello port?"},
                              [{parallelism, false}]),
     {parallelism, false} = erlang:port_info(Port2, parallelism),
-    receive 
-        {Port2, {data, "Hello port?"}} = Msg2 -> 
+    receive
+        {Port2, {data, "Hello port?"}} = Msg2 ->
             io:format("~p~n", [Msg2]),
-            ok; 
+            ok;
         Other2 ->
             ct:fail({unexpected2, Other2})
     end,
@@ -1389,20 +1449,20 @@ spawn_executable(Config) when is_list(Config) ->
     ["echo_args"] = run_echo_args(DataDir,[binary, "echo_args"]),
     ["echo_arguments"] = run_echo_args(DataDir,["echo_arguments"]),
     ["echo_arguments"] = run_echo_args(DataDir,[binary, "echo_arguments"]),
-    [ExactFile1,"hello world","dlrow olleh"] = 
+    [ExactFile1,"hello world","dlrow olleh"] =
     run_echo_args(DataDir,[ExactFile1,"hello world","dlrow olleh"]),
     [ExactFile1] = run_echo_args(DataDir,[default]),
     [ExactFile1] = run_echo_args(DataDir,[binary, default]),
-    [ExactFile1,"hello world","dlrow olleh"] = 
+    [ExactFile1,"hello world","dlrow olleh"] =
     run_echo_args(DataDir,[switch_order,ExactFile1,"hello world",
                            "dlrow olleh"]),
-    [ExactFile1,"hello world","dlrow olleh"] = 
+    [ExactFile1,"hello world","dlrow olleh"] =
     run_echo_args(DataDir,[binary,switch_order,ExactFile1,"hello world",
                            "dlrow olleh"]),
     [ExactFile1,"hello world","dlrow olleh"] =
     run_echo_args(DataDir,[default,"hello world","dlrow olleh"]),
 
-    [ExactFile1,"hello world","dlrow olleh"] = 
+    [ExactFile1,"hello world","dlrow olleh"] =
     run_echo_args_2("\""++ExactFile1++"\" "++"\"hello world\" \"dlrow olleh\""),
     [ExactFile1,"hello world","dlrow olleh"] =
     run_echo_args_2(unicode:characters_to_binary("\""++ExactFile1++"\" "++"\"hello world\" \"dlrow olleh\"")),
@@ -1418,7 +1478,7 @@ spawn_executable(Config) when is_list(Config) ->
     [ExactFile2] = run_echo_args(SpaceDir,[]),
     ["echo_args"] = run_echo_args(SpaceDir,["echo_args"]),
     ["echo_arguments"] = run_echo_args(SpaceDir,["echo_arguments"]),
-    [ExactFile2,"hello world","dlrow olleh"] = 
+    [ExactFile2,"hello world","dlrow olleh"] =
     run_echo_args(SpaceDir,[ExactFile2,"hello world","dlrow olleh"]),
     [ExactFile2,"hello world","dlrow olleh"] =
     run_echo_args(SpaceDir,[binary, ExactFile2,"hello world","dlrow olleh"]),
@@ -1429,16 +1489,16 @@ spawn_executable(Config) when is_list(Config) ->
     run_echo_args(SpaceDir,[binary, ExactFile2,"hello \"world\"","\"dlrow\" olleh"]),
 
     [ExactFile2] = run_echo_args(SpaceDir,[default]),
-    [ExactFile2,"hello world","dlrow olleh"] = 
+    [ExactFile2,"hello world","dlrow olleh"] =
     run_echo_args(SpaceDir,[switch_order,ExactFile2,"hello world", "dlrow olleh"]),
-    [ExactFile2,"hello world","dlrow olleh"] = 
+    [ExactFile2,"hello world","dlrow olleh"] =
     run_echo_args(SpaceDir,[default,"hello world","dlrow olleh"]),
-    [ExactFile2,"hello world","dlrow olleh"] = 
+    [ExactFile2,"hello world","dlrow olleh"] =
     run_echo_args_2("\""++ExactFile2++"\" "++"\"hello world\" \"dlrow olleh\""),
     [ExactFile2,"hello world","dlrow olleh"] =
     run_echo_args_2(unicode:characters_to_binary("\""++ExactFile2++"\" "++"\"hello world\" \"dlrow olleh\"")),
 
-    ExeExt = 
+    ExeExt =
     case string:to_lower(lists:last(string:tokens(ExactFile2,"."))) of
         "exe" ->
             ".exe";
@@ -1452,17 +1512,17 @@ spawn_executable(Config) when is_list(Config) ->
     [ExactFile3] = run_echo_args(SpaceDir,Executable2,[]),
     ["echo_args"] = run_echo_args(SpaceDir,Executable2,["echo_args"]),
     ["echo_arguments"] = run_echo_args(SpaceDir,Executable2,["echo_arguments"]),
-    [ExactFile3,"hello world","dlrow olleh"] = 
+    [ExactFile3,"hello world","dlrow olleh"] =
     run_echo_args(SpaceDir,Executable2,[ExactFile3,"hello world","dlrow olleh"]),
     [ExactFile3] = run_echo_args(SpaceDir,Executable2,[default]),
-    [ExactFile3,"hello world","dlrow olleh"] = 
+    [ExactFile3,"hello world","dlrow olleh"] =
     run_echo_args(SpaceDir,Executable2,
                   [switch_order,ExactFile3,"hello world",
                    "dlrow olleh"]),
-    [ExactFile3,"hello world","dlrow olleh"] = 
+    [ExactFile3,"hello world","dlrow olleh"] =
     run_echo_args(SpaceDir,Executable2,
                   [default,"hello world","dlrow olleh"]),
-    [ExactFile3,"hello world","dlrow olleh"] = 
+    [ExactFile3,"hello world","dlrow olleh"] =
     run_echo_args_2("\""++ExactFile3++"\" "++"\"hello world\" \"dlrow olleh\""),
     [ExactFile3,"hello world","dlrow olleh"] =
     run_echo_args_2(unicode:characters_to_binary("\""++ExactFile3++"\" "++"\"hello world\" \"dlrow olleh\"")),
@@ -1510,11 +1570,11 @@ test_bat_file(Dir) ->
          <<"\r\n">>],
     file:write_file(Full,list_to_binary(D)),
     EF = filename:basename(FN),
-    [DN,"hello","world"] = 
+    [DN,"hello","world"] =
     run_echo_args(Dir,FN,
                   [default,"hello","world"]),
     %% The arg0 argumant should be ignored when running batch files
-    [DN,"hello","world"] = 
+    [DN,"hello","world"] =
     run_echo_args(Dir,FN,
                   ["knaskurt","hello","world"]),
     EF = filename:basename(DN),
@@ -1533,10 +1593,10 @@ test_sh_file(Dir) ->
          <<"done\n">>],
     file:write_file(Full,list_to_binary(D)),
     chmodplusx(Full),
-    [Full,"hello","world"] = 
+    [Full,"hello","world"] =
     run_echo_args(Dir,FN,
                   [default,"hello","world"]),
-    [Full,"hello","world of spaces"] = 
+    [Full,"hello","world of spaces"] =
     run_echo_args(Dir,FN,
                   [default,"hello","world of spaces"]),
     file:write_file(filename:join([Dir,"testfile1"]),<<"testdata1">>),
@@ -1544,7 +1604,7 @@ test_sh_file(Dir) ->
     Pattern = filename:join([Dir,"testfile*"]),
     L = filelib:wildcard(Pattern),
     2 = length(L),
-    [Full,"hello",Pattern] = 
+    [Full,"hello",Pattern] =
     run_echo_args(Dir,FN,
                   [default,"hello",Pattern]),
     ok.
@@ -1620,10 +1680,10 @@ mix_up_ports(Config) when is_list(Config) ->
     ok = load_driver(Path, "echo_drv"),
     Port = erlang:open_port({spawn, "echo_drv"}, []),
     Port ! {self(), {command, "Hello port!"}},
-    receive 
-        {Port, {data, "Hello port!"}} = Msg1 -> 
+    receive
+        {Port, {data, "Hello port!"}} = Msg1 ->
             io:format("~p~n", [Msg1]),
-            ok; 
+            ok;
         Other ->
             ct:fail({unexpected, Other})
     end,
@@ -1631,7 +1691,7 @@ mix_up_ports(Config) when is_list(Config) ->
     receive {Port, closed} -> ok end,
     loop(start, done,
          fun(P) ->
-                 Q = 
+                 Q =
                  (catch erlang:open_port({spawn, "echo_drv"}, [])),
                  %%		       io:format("~p ", [Q]),
                  if is_port(Q) ->
@@ -1642,7 +1702,7 @@ mix_up_ports(Config) when is_list(Config) ->
                  end
          end),
     Port ! {self(), {command, "Hello again port!"}},
-    receive 
+    receive
         Msg2 ->
             ct:fail({unexpected, Msg2})
     after 1000 ->
@@ -1802,7 +1862,7 @@ exit_status_msb_test(Config, SleepSecs) when is_list(Config) ->
     %% We want to start port programs from as many schedulers as possible
     %% and we want these port programs to terminate while multi-scheduling
     %% is blocked.
-    %% 
+    %%
     NoSchedsOnln = erlang:system_info(schedulers_online),
     Parent = self(),
     io:format("SleepSecs = ~p~n", [SleepSecs]),
@@ -2214,7 +2274,7 @@ ports_snapshots(0, _, _) ->
     ok;
 ports_snapshots(Iter, TrafficPid, OtherPorts) ->
 
-    TrafficPid ! start,    
+    TrafficPid ! start,
     receive after 1 -> ok end,
 
     Snapshot = erlang:ports(),
@@ -2243,7 +2303,7 @@ ports_traffic_stopped(MaxPorts, {PortList, PortCnt}) ->
     end.
 
 ports_traffic_started(MaxPorts, {PortList, PortCnt}, EventList) ->
-    receive 
+    receive
         {Pid, stop} ->
             %%io:format("Traffic stopped in ~p\n",[self()]),
             Pid ! {self(), EventList, PortList},
@@ -2256,7 +2316,7 @@ ports_traffic_started(MaxPorts, {PortList, PortCnt}, EventList) ->
 ports_traffic_do(MaxPorts, {PortList, PortCnt}, EventList) ->
     N = uniform(MaxPorts),
     case N > PortCnt of
-        true -> % Open port	    
+        true -> % Open port
             P = open_port({spawn, "exit_drv"}, []),
             %%io:format("Created port ~p\n",[P]),
             ports_traffic_started(MaxPorts, {[P|PortList], PortCnt+1},
@@ -2270,7 +2330,7 @@ ports_traffic_do(MaxPorts, {PortList, PortCnt}, EventList) ->
                                   [{close,P}|EventList])
     end.
 
-ports_verify(Ports, PortsAfter, EventList) ->    
+ports_verify(Ports, PortsAfter, EventList) ->
     %%io:format("Candidate=~p\nEvents=~p\n", [PortsAfter, EventList]),
     case lists:sort(Ports) =:= lists:sort(PortsAfter) of
         true ->
@@ -2280,10 +2340,10 @@ ports_verify(Ports, PortsAfter, EventList) ->
             %% Note that we track the event list "backwards", undoing open/close:
             case EventList of
                 [{open,P} | Tail] ->
-                    ports_verify(Ports, lists:delete(P,PortsAfter), Tail);		    
+                    ports_verify(Ports, lists:delete(P,PortsAfter), Tail);
 
                 [{close,P} | Tail] ->
-                    ports_verify(Ports, [P | PortsAfter], Tail);		    
+                    ports_verify(Ports, [P | PortsAfter], Tail);
 
                 [] ->
                     ct:fail("Inconsistent snapshot from erlang:ports()")
@@ -2391,3 +2451,227 @@ wait_until(Fun) ->
             receive after 100 -> ok end,
             wait_until(Fun)
     end.
+
+%% Attempt to monitor pid as port, and port as pid
+mon_port_invalid_type(_Config) ->
+    Port = hd(erlang:ports()),
+    ?assertError(badarg, erlang:monitor(port, self())),
+    ?assertError(badarg, erlang:monitor(process, Port)),
+    ok.
+
+%% With local port
+mon_port_local(Config) ->
+    Port1 = create_port(Config, ["-h1", "-q"]), % will close after we send 1 byte
+    Ref1 = erlang:monitor(port, Port1),
+    ?assertMatch({proc_monitors, true, port_monitored_by, true},
+                 port_is_monitored(self(), Port1)),
+    Port1 ! {self(), {command, <<"1">>}}, % port test will close self immediately
+    receive ExitP1 -> ?assertMatch({'DOWN', Ref1, port, Port1, _}, ExitP1)
+    after 1000 -> ?assert(false) end,
+    ?assertMatch({proc_monitors, false, port_monitored_by, false},
+                 port_is_monitored(self(), Port1)),
+
+    %% Trying to re-monitor a port which exists but is not healthy will
+    %% succeed but then will immediately send DOWN
+    Ref2 = erlang:monitor(port, Port1),
+    receive ExitP2 -> ?assertMatch({'DOWN', Ref2, port, Port1, _}, ExitP2)
+    after 1000 -> ?assert(false) end,
+    ok.
+
+%% With remote port on remote node (should fail)
+mon_port_remote_on_remote(_Config) ->
+    Port3 = binary_to_term(<<131, 102,          % Ext term format: PORT_EXT
+                             100, 0, 13, "fgsfds@fgsfds", % Node :: ATOM_EXT
+                             1:32/big,          % Id
+                             0>>),              % Creation
+    ?assertError(badarg, erlang:monitor(port, Port3)),
+    ok.
+
+%% Remote port belongs to this node and does not exist
+%% Port4 produces #Port<0.167772160> which should not exist in a test run
+mon_port_bad_remote_on_local(_Config) ->
+    Port4 = binary_to_term(<<131, 102,          % Ext term format: PORT_EXT
+                             100, 0, 13, "nonode@nohost", % Node
+                             167772160:32/big,  % Id
+                             0>>),              % Creation
+    ?assertError(badarg, erlang:monitor(port, Port4)),
+    ok.
+
+%% Monitor owner (origin) dies before port is closed
+mon_port_origin_dies(Config) ->
+    Port5 = create_port(Config, ["-h1", "-q"]), % will close after we send 1 byte
+    Self5 = self(),
+    Proc5 = spawn(fun() ->
+                      Self5 ! test5_started,
+                      erlang:monitor(port, Port5),
+                      receive stop -> ok end
+                  end),
+    erlang:monitor(process, Proc5), % we want to sync with its death
+    receive test5_started -> ok
+    after 1000 -> ?assert(false) end,
+    ?assertMatch({proc_monitors, true, port_monitored_by, true},
+                 port_is_monitored(Proc5, Port5)),
+    Proc5 ! stop,
+    % receive from monitor (removing race condition)
+    receive ExitP5 -> ?assertMatch({'DOWN', _, process, Proc5, _}, ExitP5)
+    after 1000 -> ?assert(false) end,
+    ?assertMatch({proc_monitors, false, port_monitored_by, false},
+                 port_is_monitored(Proc5, Port5)),
+    Port5 ! {self(), {command, <<"1">>}}, % make port quit
+    ok.
+
+%% Monitor a named port
+mon_port_named(Config) ->
+    Name6 = test_port6,
+    Port6 = create_port(Config, ["-h1", "-q"]), % will close after we send 1 byte
+    erlang:register(Name6, Port6),
+    erlang:monitor(port, Name6),
+    ?assertMatch({proc_monitors, true, port_monitored_by, true},
+                 port_is_monitored(self(), Name6)),
+    Port6 ! {self(), {command, <<"1">>}}, % port test will close self immediately
+    receive ExitP6 -> ?assertMatch({'DOWN', _, port, {Name6, _}, _}, ExitP6)
+    after 1000 -> ?assert(false) end,
+    ?assertMatch({proc_monitors, false, port_monitored_by, false},
+                 port_is_monitored(self(), Name6)),
+    ok.
+
+%% Named does not exist: Should succeed but immediately send 'DOWN'
+mon_port_bad_named(_Config) ->
+    Name7 = test_port7,
+    erlang:monitor(port, Name7),
+    receive {'DOWN', _, port, {Name7, _}, noproc} -> ok
+    after 1000 -> ?assert(false) end,
+    ok.
+
+%% Monitor a pid and demonitor by ref
+mon_port_pid_demonitor(Config) ->
+    Port8 = create_port(Config, ["-h1", "-q"]), % will close after we send 1 byte
+    Ref8 = erlang:monitor(port, Port8),
+    ?assertMatch({proc_monitors, true, port_monitored_by, true},
+                 port_is_monitored(self(), Port8)),
+    erlang:demonitor(Ref8),
+    ?assertMatch({proc_monitors, false, port_monitored_by, false},
+                 port_is_monitored(self(), Port8)),
+    Port8 ! {self(), {command, <<"1">>}}, % port test will close self immediately
+    ok.
+
+%% Monitor by name and demonitor by ref
+mon_port_name_demonitor(Config) ->
+    Name9 = test_port9,
+    Port9 = create_port(Config, ["-h1", "-q"]), % will close after we send 1 byte
+    erlang:register(Name9, Port9),
+    Ref9 = erlang:monitor(port, Name9),
+    ?assertMatch({proc_monitors, true, port_monitored_by, true},
+                 port_is_monitored(self(), Name9)),
+    erlang:demonitor(Ref9),
+    ?assertMatch({proc_monitors, false, port_monitored_by, false},
+                 port_is_monitored(self(), Name9)),
+    Port9 ! {self(), {command, <<"1">>}}, % port test will close self immediately
+    ok.
+
+%% 1. Spawn a port which will sleep 3 seconds
+%% 2. Port driver and dies horribly (via C driver_failure call). This should
+%%    mark port as exiting or something.
+%% 3. While the command happens, a monitor is requested on the port
+mon_port_driver_die(Config) ->
+    erlang:process_flag(scheduler, 1),
+
+    Path = proplists:get_value(data_dir, Config),
+    ok = load_driver(Path, "sleep_failure_drv"),
+    Port = open_port({spawn, "sleep_failure_drv"}, []),
+
+    Self = self(),
+    erlang:spawn_opt(fun() ->
+                             timer:sleep(250),
+                             Ref = erlang:monitor(port, Port),
+                             %% Now check that msg actually arrives
+                             receive
+                                 {'DOWN', Ref, _Port2, _, _} = M -> Self ! M
+                             after 3000 -> Self ! no_down_message
+                             end
+                     end,[{scheduler, 2}]),
+    Port ! {self(), {command, "Fail, please!"}},
+    receive
+        A when is_atom(A) -> ?assertEqual(A, 'A_should_be_printed');
+        {'DOWN', _R, port, Port, noproc} -> ok;
+        {'DOWN', _R, _P, _, _} = M -> ct:fail({got_wrong_down,M})
+    after 5000 -> ?assert(false)
+    end,
+    ok.
+
+
+%% 1. Spawn a port which will sleep 3 seconds
+%% 2. Monitor port
+%% 3. Port driver and dies horribly (via C driver_failure call). This should
+%%    mark port as exiting or something.
+%% 4. While the command happens, a demonitor is requested on the port
+mon_port_driver_die_demonitor(Config) ->
+    erlang:process_flag(scheduler, 1),
+
+    Path = proplists:get_value(data_dir, Config),
+    ok = load_driver(Path, "sleep_failure_drv"),
+    Port = open_port({spawn, "sleep_failure_drv"}, []),
+
+    Self = self(),
+    erlang:spawn_opt(
+      fun() ->
+              Ref = erlang:monitor(port, Port),
+              Self ! Ref,
+              timer:sleep(250),
+              erlang:demonitor(Ref),
+              %% Now check that msg still arrives,
+              %% the demon should have arrived after
+              %% the port exited
+              receive
+                  {'DOWN', Ref, _Port2, _, _} = M -> Self ! M
+              after 3000 -> Self ! no_down_message
+              end
+      end,[{scheduler, 2}]),
+    Ref = receive R -> R end,
+    Port ! {self(), {command, "Fail, please!"}},
+    receive
+        {'DOWN', Ref, port, Port, normal} -> ok;
+        {'DOWN', _R, _P, _, _} = M -> ct:fail({got_wrong_down,M})
+    after 5000 -> ?assert(false)
+    end,
+    ok.
+
+%% @doc Makes a controllable port for testing. Underlying mechanism of this
+%% port is not important, only important is our ability to close/kill it or
+%% have it monitored.
+create_port(Config, Args) ->
+    DataDir = ?config(data_dir, Config),
+    %% Borrow port test utility from port SUITE
+    Program = filename:join([DataDir, "port_test"]),
+    erlang:open_port({spawn_executable, Program}, [{args, Args}]).
+
+%% @doc Checks if process Pid exists, and if so, if its monitoring (or not)
+%% the Port (or if port doesn't exist, we assume answer is no).
+port_is_monitored(Pid, Port) when is_pid(Pid), is_port(Port) ->
+    %% Variant for when port is a port id (port())
+    A = case erlang:process_info(Pid, monitors) of
+            undefined -> false;
+            {monitors, ProcMTargets} -> lists:member({port, Port}, ProcMTargets)
+        end,
+    B = case erlang:port_info(Port, monitored_by) of
+            undefined -> false;
+            {monitored_by, PortMonitors} -> lists:member(Pid, PortMonitors)
+        end,
+    {proc_monitors, A, port_monitored_by, B};
+port_is_monitored(Pid, PortName) when is_pid(Pid), is_atom(PortName) ->
+    %% Variant for when port is an atom
+    A = case erlang:process_info(Pid, monitors) of
+        undefined -> false;
+        {monitors, ProcMTargets} ->
+            lists:member({port, {PortName, node()}}, ProcMTargets)
+    end,
+    B = case erlang:whereis(PortName) of
+            undefined -> false; % name is not registered or is dead
+            PortId ->
+                case erlang:port_info(PortId, monitored_by) of
+                    undefined -> false; % is dead
+                    {monitored_by, PortMonitors} ->
+                        lists:member(Pid, PortMonitors)
+                end
+        end,
+    {proc_monitors, A, port_monitored_by, B}.
diff --git a/erts/emulator/test/port_SUITE_data/Makefile.src b/erts/emulator/test/port_SUITE_data/Makefile.src
index ff822ae720..fb7685c4b6 100644
--- a/erts/emulator/test/port_SUITE_data/Makefile.src
+++ b/erts/emulator/test/port_SUITE_data/Makefile.src
@@ -4,7 +4,7 @@ CFLAGS = @CFLAGS@ -I@erl_include@ @DEFS@
 CROSSLDFLAGS = @CROSSLDFLAGS@
 
 PROGS = port_test@exe@ echo_args@exe@ dead_port@exe@
-DRIVERS = echo_drv@dll@ exit_drv@dll@ failure_drv@dll@
+DRIVERS = echo_drv@dll@ exit_drv@dll@ failure_drv@dll@ sleep_failure_drv@dll@
 
 all: $(PROGS) $(DRIVERS) port_test.@EMULATOR@
 
diff --git a/erts/emulator/test/port_SUITE_data/sleep_failure_drv.c b/erts/emulator/test/port_SUITE_data/sleep_failure_drv.c
new file mode 100644
index 0000000000..1f52646572
--- /dev/null
+++ b/erts/emulator/test/port_SUITE_data/sleep_failure_drv.c
@@ -0,0 +1,76 @@
+#include <stdio.h>
+#include "erl_driver.h"
+#ifdef __WIN32__
+#    include <windows.h>
+#else
+#    include <unistd.h>
+#endif
+
+typedef struct _erl_drv_data FailureDrvData;
+
+static FailureDrvData *failure_drv_start(ErlDrvPort, char *);
+static void failure_drv_stop(FailureDrvData *);
+static void failure_drv_output(ErlDrvData, char *, ErlDrvSizeT);
+static void failure_drv_finish(void);
+
+static ErlDrvEntry failure_drv_entry = { 
+    NULL, /* init */
+    failure_drv_start,
+    failure_drv_stop,
+    failure_drv_output,
+    NULL, /* ready_input */
+    NULL, /* ready_output */
+    "sleep_failure_drv",
+    NULL, /* finish */
+    NULL, /* handle */
+    NULL, /* control */
+    NULL, /* timeout */
+    NULL, /* outputv */
+    NULL, /* ready_async */
+    NULL,
+    NULL,
+    NULL,
+    ERL_DRV_EXTENDED_MARKER,
+    ERL_DRV_EXTENDED_MAJOR_VERSION,
+    ERL_DRV_EXTENDED_MINOR_VERSION,
+    0,
+    NULL,
+    NULL,
+    NULL,
+};
+
+
+
+/* -------------------------------------------------------------------------
+** Entry functions
+**/
+
+DRIVER_INIT(failure_drv)
+{
+    return &failure_drv_entry;
+}
+
+static FailureDrvData *failure_drv_start(ErlDrvPort port, char *command) {
+    void *void_ptr;
+
+    return void_ptr = port;
+}
+
+static void failure_drv_stop(FailureDrvData *data_p) {
+}
+
+static void failure_drv_output(ErlDrvData drv_data, char *buf, ErlDrvSizeT len) {
+    FailureDrvData *data_p = (FailureDrvData *) drv_data;
+    void *void_ptr;
+    ErlDrvPort port = void_ptr = data_p;
+
+#ifdef __WIN32__
+    Sleep(3000);
+#else
+    sleep(3);
+#endif
+    driver_failure(port, 0);
+}
+
+static void failure_drv_finish() {
+}
diff --git a/erts/preloaded/src/erlang.erl b/erts/preloaded/src/erlang.erl
index 94f3078173..edf79b8f75 100644
--- a/erts/preloaded/src/erlang.erl
+++ b/erts/preloaded/src/erlang.erl
@@ -1206,16 +1206,18 @@ module_loaded(_Module) ->
     erlang:nif_error(undefined).
 
 -type registered_name() :: atom().
-
 -type registered_process_identifier() :: registered_name() | {registered_name(), node()}.
-
 -type monitor_process_identifier() :: pid() | registered_process_identifier().
+-type monitor_port_identifier() :: port() | registered_name().
 
 %% monitor/2
--spec monitor(process, monitor_process_identifier()) -> MonitorRef when
-      MonitorRef :: reference();
-	     (time_offset, clock_service) -> MonitorRef when
-      MonitorRef :: reference().
+-spec monitor
+      (process, monitor_process_identifier()) -> MonitorRef
+	  when MonitorRef :: reference();
+      (port, monitor_port_identifier()) -> MonitorRef
+	  when MonitorRef :: reference();
+	    (time_offset, clock_service) -> MonitorRef
+	  when MonitorRef :: reference().
 
 monitor(_Type, _Item) ->
     erlang:nif_error(undefined).
@@ -2160,7 +2162,7 @@ process_flag(_Flag, _Value) ->
       {max_heap_size, MaxHeapSize :: max_heap_size()} |
       {monitored_by, Pids :: [pid()]} |
       {monitors,
-       Monitors :: [{process, Pid :: pid() |
+       Monitors :: [{process | port, Pid :: pid() | port() |
                                      {RegName :: atom(), Node :: node()}}]} |
       {message_queue_data, MQD :: message_queue_data()} |
       {priority, Level :: priority_level()} |
@@ -3087,6 +3089,9 @@ port_info(Port) ->
 		      (Port, monitors) -> {monitors, Monitors} | 'undefined' when
       Port :: port() | atom(),
       Monitors :: [{process, pid()}];
+		      (Port, monitored_by) -> {monitored_by, MonitoredBy} | 'undefined' when
+      Port :: port() | atom(),
+      MonitoredBy :: [pid()];
 		      (Port, name) -> {name, Name} | 'undefined' when
       Port :: port() | atom(),
       Name :: string();