erts: Add ERL_NIF_SELECT_CANCEL flag for enif_select

to deselect read and/or writes without stop callback.

5 files changed, 100 insertions, 35 deletions

diff --git a/erts/doc/src/erl_nif.xml b/erts/doc/src/erl_nif.xml
index a20b8ee884..a5826307f7 100644
--- a/erts/doc/src/erl_nif.xml
+++ b/erts/doc/src/erl_nif.xml
@@ -3037,7 +3037,8 @@ enif_map_iterator_destroy(env, &amp;iter);</code>
 	<p>Argument <c>mode</c> describes the type of events to wait for. It can be
 	  <c>ERL_NIF_SELECT_READ</c>, <c>ERL_NIF_SELECT_WRITE</c> or a bitwise
 	  OR combination to wait for both. It can also be <c>ERL_NIF_SELECT_STOP</c>
-	  which is described further below. When a read or write event is triggered,
+	  or <c>ERL_NIF_SELECT_CANCEL</c> which are described further
+	  below. When a read or write event is triggered,
 	  a notification message like this is sent to the process identified by
 	  <c>pid</c>:</p>
 	<code type="none">{select, Obj, Ref, ready_input | ready_output}</code>
@@ -3058,13 +3059,21 @@ enif_map_iterator_destroy(env, &amp;iter);</code>
 	<p>The notifications are one-shot only. To receive further notifications of the same
 	  type (read or write), repeated calls to <c>enif_select</c> must be made
 	  after receiving each notification.</p>
+	<p><c>ERL_NIF_SELECT_CANCEL</c> can be used to cancel previously
+	  selected events. It must be used in a bitwise OR combination with
+	  <c>ERL_NIF_SELECT_READ</c> and/or <c>ERL_NIF_SELECT_WRITE</c> to
+	  indicate which type of event to cancel. The return value will
+	  tell if the event was actualy cancelled or if a notification may
+	  already have been sent.</p>
 	<p>Use <c>ERL_NIF_SELECT_STOP</c> as <c>mode</c> in order to safely
 	  close an event object that has been passed to <c>enif_select</c>. The
 	  <seealso marker="#ErlNifResourceStop"><c>stop</c></seealso> callback
 	  of the resource <c>obj</c> will be called when it is safe to close
 	  the event object. This safe way of closing event objects must be used
-	  even if all notifications have been received and no further calls to
-	  <c>enif_select</c> have been made.</p>
+	  even if all notifications have been received (or cancelled) and no
+	  further calls to <c>enif_select</c> have been made.
+	  <c>ERL_NIF_SELECT_STOP</c> will first cancel any selected events
+	  before it calls or schedules the <c>stop</c> callback.</p>
 	<p>The first call to <c>enif_select</c> for a specific OS <c>event</c> will establish
 	  a relation between the event object and the containing resource. All subsequent calls
 	  for an <c>event</c> must pass its containing resource as argument
@@ -3086,7 +3095,15 @@ enif_map_iterator_destroy(env, &amp;iter);</code>
           <item>The stop callback was called directly by <c>enif_select</c>.</item>
           <tag><c>ERL_NIF_SELECT_STOP_SCHEDULED</c></tag>
           <item>The stop callback was scheduled to run on some other thread
-	    or later by this thread.</item>
+	  or later by this thread.</item>
+	  <tag><c>ERL_NIF_SELECT_READ_CANCELLED</c></tag>
+          <item>A read event was cancelled by <c>ERL_NIF_SELECT_CANCEL</c> or
+	  <c>ERL_NIF_SELECT_STOP</c> and is guaranteed not to generate a
+	  <c>ready_input</c> notification message.</item>
+	  <tag><c>ERL_NIF_SELECT_WRITE_CANCELLED</c></tag>
+          <item>A write event was cancelled by <c>ERL_NIF_SELECT_CANCEL</c> or
+	  <c>ERL_NIF_SELECT_STOP</c> and is guaranteed not to generate a
+	  <c>ready_output</c> notification message.</item>
 	</taglist>
 	<p>Returns a negative value if the call failed where the following bits can be set:</p>
         <taglist>
@@ -3112,6 +3129,11 @@ if (retval &amp; ERL_NIF_SELECT_STOP_CALLED) {
 }
 </code>
         </note>
+	<note><p>The mode flag <c>ERL_NIF_SELECT_CANCEL</c> and the return flags
+	  <c>ERL_NIF_SELECT_READ_CANCELLED</c> and
+	  <c>ERL_NIF_SELECT_WRITE_CANCELLED</c> were introduced in erts-11.0
+	  (OTP-22.0).</p>
+	</note>
       </desc>
     </func>
 
diff --git a/erts/emulator/beam/erl_drv_nif.h b/erts/emulator/beam/erl_drv_nif.h
index 31b4817fb1..9ef7c39d41 100644
--- a/erts/emulator/beam/erl_drv_nif.h
+++ b/erts/emulator/beam/erl_drv_nif.h
@@ -53,7 +53,8 @@ typedef enum {
 enum ErlNifSelectFlags {
     ERL_NIF_SELECT_READ      = (1 << 0),
     ERL_NIF_SELECT_WRITE     = (1 << 1),
-    ERL_NIF_SELECT_STOP      = (1 << 2)
+    ERL_NIF_SELECT_STOP      = (1 << 2),
+    ERL_NIF_SELECT_CANCEL    = (1 << 3)
 };
 
 /*
diff --git a/erts/emulator/beam/erl_nif.h b/erts/emulator/beam/erl_nif.h
index 4c09496ef1..c5227a0c23 100644
--- a/erts/emulator/beam/erl_nif.h
+++ b/erts/emulator/beam/erl_nif.h
@@ -160,6 +160,8 @@ typedef int ErlNifEvent;
 #define ERL_NIF_SELECT_STOP_SCHEDULED (1 << 1)
 #define ERL_NIF_SELECT_INVALID_EVENT  (1 << 2)
 #define ERL_NIF_SELECT_FAILED         (1 << 3)
+#define ERL_NIF_SELECT_READ_CANCELLED (1 << 4)
+#define ERL_NIF_SELECT_WRITE_CANCELLED (1 << 5)
 
 typedef enum
 {
diff --git a/erts/emulator/sys/common/erl_check_io.c b/erts/emulator/sys/common/erl_check_io.c
index 3e77dce1cd..b03e19ee71 100644
--- a/erts/emulator/sys/common/erl_check_io.c
+++ b/erts/emulator/sys/common/erl_check_io.c
@@ -916,7 +916,7 @@ enif_select(ErlNifEnv* env,
         ctl_op = ERTS_POLL_OP_DEL;
     }
     else {
-        on = 1;
+        on = !(mode & ERL_NIF_SELECT_CANCEL);
         ASSERT(mode);
         if (mode & ERL_DRV_READ) {
             ctl_events |= ERTS_POLL_EV_IN;
@@ -1042,38 +1042,51 @@ enif_select(ErlNifEnv* env,
         ret = 0;
     }
     else { /* off */
+        ret = 0;
         if (state->type == ERTS_EV_TYPE_NIF) {
-            state->driver.nif->in.pid = NIL;
-            state->driver.nif->out.pid = NIL;
-        }
-        ASSERT(state->events==0);
-        if (!wake_poller) {
-            /*
-             * Safe to close fd now as it is not in pollset
-             * or there was no need to eject fd (kernel poll)
-             */
-            if (state->type == ERTS_EV_TYPE_NIF) {
-                ASSERT(state->driver.stop.resource == resource);
-                call_stop = CALL_STOP_AND_RELEASE;
-                state->driver.stop.resource = NULL;
+            if (mode & ERL_NIF_SELECT_READ
+                && is_not_nil(state->driver.nif->in.pid)) {
+                state->driver.nif->in.pid = NIL;
+                ret |= ERL_NIF_SELECT_READ_CANCELLED;
             }
-            else {
-                ASSERT(!state->driver.stop.resource);
-                call_stop = CALL_STOP;
+            if (mode & ERL_NIF_SELECT_WRITE
+                && is_not_nil(state->driver.nif->out.pid)) {
+                state->driver.nif->out.pid = NIL;
+                ret |= ERL_NIF_SELECT_WRITE_CANCELLED;
             }
-            state->type = ERTS_EV_TYPE_NONE;
-            ret = ERL_NIF_SELECT_STOP_CALLED;
         }
-        else {
-            /* Not safe to close fd, postpone stop_select callback. */
-            if (state->type == ERTS_EV_TYPE_NONE) {
-                ASSERT(!state->driver.stop.resource);
-                state->driver.stop.resource = resource;
-                enif_keep_resource(resource);
+        if (mode & ERL_NIF_SELECT_STOP) {
+            ASSERT(state->events==0);
+            if (!wake_poller) {
+                /*
+                 * Safe to close fd now as it is not in pollset
+                 * or there was no need to eject fd (kernel poll)
+                 */
+                if (state->type == ERTS_EV_TYPE_NIF) {
+                    ASSERT(state->driver.stop.resource == resource);
+                    call_stop = CALL_STOP_AND_RELEASE;
+                    state->driver.stop.resource = NULL;
+                }
+                else {
+                    ASSERT(!state->driver.stop.resource);
+                    call_stop = CALL_STOP;
+                }
+                state->type = ERTS_EV_TYPE_NONE;
+                ret |= ERL_NIF_SELECT_STOP_CALLED;
+            }
+            else {
+                /* Not safe to close fd, postpone stop_select callback. */
+                if (state->type == ERTS_EV_TYPE_NONE) {
+                    ASSERT(!state->driver.stop.resource);
+                    state->driver.stop.resource = resource;
+                    enif_keep_resource(resource);
+                }
+                state->type = ERTS_EV_TYPE_STOP_NIF;
+                ret |= ERL_NIF_SELECT_STOP_SCHEDULED;
             }
-            state->type = ERTS_EV_TYPE_STOP_NIF;
-            ret = ERL_NIF_SELECT_STOP_SCHEDULED;
         }
+        else
+            ASSERT(mode & ERL_NIF_SELECT_CANCEL);
     }
 
 done:
@@ -1251,7 +1264,8 @@ print_nif_select_op(erts_dsprintf_buf_t *dsbufp,
 		  (int) fd,
 		  mode & ERL_NIF_SELECT_READ ? " READ" : "",
 		  mode & ERL_NIF_SELECT_WRITE ? " WRITE" : "",
-		  mode & ERL_NIF_SELECT_STOP ? " STOP" : "",
+		  (mode & ERL_NIF_SELECT_STOP ? " STOP"
+                   : (mode & ERL_NIF_SELECT_CANCEL ? " CANCEL" : "")),
 		  resource->type->module,
                   resource->type->name,
                   ref);
@@ -2333,10 +2347,16 @@ drvmode2str(int mode) {
 
 static ERTS_INLINE char *
 nifmode2str(enum ErlNifSelectFlags mode) {
+    if (mode & ERL_NIF_SELECT_STOP)
+        return "STOP";
     switch (mode) {
     case ERL_NIF_SELECT_READ: return "READ";
     case ERL_NIF_SELECT_WRITE: return "WRITE";
-    case ERL_NIF_SELECT_STOP: return "STOP";
+    case ERL_NIF_SELECT_READ|ERL_NIF_SELECT_WRITE: return "READ|WRITE";
+    case ERL_NIF_SELECT_CANCEL|ERL_NIF_SELECT_READ: return "CANCEL|READ";
+    case ERL_NIF_SELECT_CANCEL|ERL_NIF_SELECT_WRITE: return "CANCEL|WRITE";
+    case ERL_NIF_SELECT_CANCEL|ERL_NIF_SELECT_READ|ERL_NIF_SELECT_WRITE:
+        return "CANCEL|READ|WRITE";
     default: return "UNKNOWN";
     }
 }
diff --git a/erts/emulator/test/nif_SUITE.erl b/erts/emulator/test/nif_SUITE.erl
index 7c85cf2259..87cf7bf81d 100644
--- a/erts/emulator/test/nif_SUITE.erl
+++ b/erts/emulator/test/nif_SUITE.erl
@@ -484,12 +484,14 @@ t_on_load(Config) when is_list(Config) ->
 -define(ERL_NIF_SELECT_READ, (1 bsl 0)).
 -define(ERL_NIF_SELECT_WRITE, (1 bsl 1)).
 -define(ERL_NIF_SELECT_STOP, (1 bsl 2)).
+-define(ERL_NIF_SELECT_CANCEL, (1 bsl 3)).
 
 -define(ERL_NIF_SELECT_STOP_CALLED, (1 bsl 0)).
 -define(ERL_NIF_SELECT_STOP_SCHEDULED, (1 bsl 1)).
 -define(ERL_NIF_SELECT_INVALID_EVENT, (1 bsl 2)).
 -define(ERL_NIF_SELECT_FAILED, (1 bsl 3)).
-
+-define(ERL_NIF_SELECT_READ_CANCELLED, (1 bsl 4)).
+-define(ERL_NIF_SELECT_WRITE_CANCELLED, (1 bsl 5)).
 
 select(Config) when is_list(Config) ->
     ensure_lib_loaded(Config),
@@ -515,7 +517,16 @@ select(Config) when is_list(Config) ->
                      end),
     0 = select_nif(R,?ERL_NIF_SELECT_READ,R,Pid,Ref),
     {Pid, done} = receive_any(1000),
+
+    %% Cancel read
+    0 = select_nif(R,?ERL_NIF_SELECT_READ bor ?ERL_NIF_SELECT_CANCEL,R,null,Ref),
     <<"hej">> = read_nif(R, 3),
+    0 = select_nif(R,?ERL_NIF_SELECT_READ,R,null,Ref),
+    ?ERL_NIF_SELECT_READ_CANCELLED =
+        select_nif(R,?ERL_NIF_SELECT_READ bor ?ERL_NIF_SELECT_CANCEL,R,null,Ref),
+    ok = write_nif(W, <<"hej again">>),
+    [] = flush(0),
+    <<"hej again">> = read_nif(R, 9),
 
     %% Wait for write
     Written = write_full(W, $a),
@@ -524,6 +535,15 @@ select(Config) when is_list(Config) ->
     Written = read_nif(R,byte_size(Written)),
     [{select, W, Ref, ready_output}] = flush(),
 
+    %% Cancel write
+    0 = select_nif(W,?ERL_NIF_SELECT_WRITE bor ?ERL_NIF_SELECT_CANCEL,W,null,Ref),
+    Written2 = write_full(W, $b),
+    0 = select_nif(W,?ERL_NIF_SELECT_WRITE,W,null,Ref),
+    ?ERL_NIF_SELECT_WRITE_CANCELLED =
+        select_nif(W,?ERL_NIF_SELECT_WRITE bor ?ERL_NIF_SELECT_CANCEL,W,null,Ref),
+    Written2 = read_nif(R,byte_size(Written2)),
+    [] = flush(0),
+
     %% Close write and wait for EOF
     eagain = read_nif(R, 1),
     check_stop_ret(select_nif(W,?ERL_NIF_SELECT_STOP,W,null,Ref)),