From 4c5d33114edea787833d6aa1b0d51ea9d98b3321 Mon Sep 17 00:00:00 2001
From: Sverker Eriksson <sverker@erlang.org>
Date: Fri, 16 Dec 2016 19:30:22 +0100
Subject: Add ErlNifSelectReturn

---
 erts/doc/src/erl_nif.xml | 35 +++++++++++++++++++++++++++++++++--
 1 file changed, 33 insertions(+), 2 deletions(-)

(limited to 'erts/doc')

diff --git a/erts/doc/src/erl_nif.xml b/erts/doc/src/erl_nif.xml
index 94aff7c67b..13b72863f3 100644
--- a/erts/doc/src/erl_nif.xml
+++ b/erts/doc/src/erl_nif.xml
@@ -2526,7 +2526,7 @@ enif_map_iterator_destroy(env, &amp;iter);</code>
     </func>
 
     <func>
-      <name><ret>int</ret>
+      <name><ret>enum ErlNifSelectReturn</ret>
         <nametext>enif_select(ErlNifEnv* env, ErlNifEvent event,
 	                      enum ErlNifSelectFlags mode, void* obj, Eterm ref)</nametext>
       </name>
@@ -2567,7 +2567,38 @@ enif_map_iterator_destroy(env, &amp;iter);</code>
 	  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>
-	<p>Returns 0 on success, or -1 if invalid arguments.</p>
+	<p>Returns an integer where different bits indicate the outcome of the call:</p>
+        <taglist>
+          <tag><c>ERL_NIF_SELECT_ERROR</c></tag>
+          <item>The master error bit. It will always be set if the call failed for
+	    any reason.</item>
+          <tag><c>ERL_NIF_SELECT_STOP_CALLED</c></tag>
+          <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>
+          <tag><c>ERL_NIF_SELECT_INVALID_EVENT</c></tag>
+          <item>Argument <c>event</c> is not a valid OS event object.</item>
+          <tag><c>ERL_NIF_SELECT_FAILED</c></tag>
+          <item>The system call failed to add the event object to the poll set.</item>
+        </taglist>
+	<p>The return value from a successful call with <c>mode</c> as <c>ERL_NIF_SELECT_STOP</c>,
+	will contain either bit <c>ERL_NIF_SELECT_STOP_CALLED</c> or
+	<c>ERL_NIF_SELECT_STOP_SCHEDULED</c>.</p>
+        <note>
+          <p>Always use bitwise AND to test the return value. New significant bits
+	  may be added in future releases to give more detailed information for both
+	  failed and successful calls. Do NOT use equallity tests like <c>==</c>, as
+	  that may cause your application to stop working.</p>
+	  <p>Example:</p>
+	  <code type="none">
+retval = enif_select(env, fd, ERL_NIF_SELECT_READ, resource, ref);
+if (retval &amp; ERL_NIF_SELECT_ERROR) {
+    /* handle error */
+}
+/* Success! */
+</code>
+        </note>
       </desc>
     </func>
 
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