erts: Add port monitors

* erlang:monitor/2 with port argument is added, erlang:demonitor, using port task API and avoiding locking;
* port_info and process_info support for monitored ports (with named port monitors support);
* Exit signals contain type 'process' or 'port';
* Propagation of port exit signals;
* Self-cleaning when origin process dies with monitor on;
* 8 test cases + testcase for port driver crashing;
* Documentation for all of the above (monitor, demonitor, port_info and process_info) updated

8 files changed, 783 insertions, 255 deletions

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 37f4e1de49..208935bed9 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 c0b1d7246c..2c3d1bb7eb 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,