Allow unexpected driver input event in driver_SUITE:smp_select

epoll on Linux has been seen to sometimes trigger unexpected
events. Most of the time these events are filtered by erl_check_io,
but may slip up to the driver in cases when fd's are reused.

Also made clear in driver docs that spurious events may happen.

3 files changed, 19 insertions, 6 deletions

diff --git a/erts/doc/src/driver_entry.xml b/erts/doc/src/driver_entry.xml
index dd949d4048..7d1585f483 100644
--- a/erts/doc/src/driver_entry.xml
+++ b/erts/doc/src/driver_entry.xml
@@ -4,7 +4,7 @@
 <cref>
   <header>
     <copyright>
-      <year>2001</year><year>2010</year>
+      <year>2001</year><year>2011</year>
       <holder>Ericsson AB. All Rights Reserved.</holder>
     </copyright>
     <legalnotice>
@@ -219,6 +219,10 @@ typedef struct erl_drv_entry {
           completes, write to the pipe (use <c>SetEvent</c> on
           Windows), this will make the emulator call
           <c>ready_input</c> or <c>ready_output</c>.</p>
+          <p>Spurious events may happen. That is, calls to <c>ready_input</c>
+          or <c>ready_output</c> even though no real events are signaled. In
+          reality it should be rare (and OS dependant), but a robust driver
+          must nevertheless be able to handle such cases.</p>
       </item>
       <tag><marker id="driver_name"/>char *driver_name</tag>
       <item>
diff --git a/erts/emulator/test/driver_SUITE.erl b/erts/emulator/test/driver_SUITE.erl
index 39b2ed395f..e029e4ec87 100644
--- a/erts/emulator/test/driver_SUITE.erl
+++ b/erts/emulator/test/driver_SUITE.erl
@@ -1,7 +1,7 @@
 %%
 %% %CopyrightBegin%
 %% 
-%% Copyright Ericsson AB 1997-2009. All Rights Reserved.
+%% Copyright Ericsson AB 1997-2011. All Rights Reserved.
 %% 
 %% The contents of this file are subject to the Erlang Public License,
 %% Version 1.1, (the "License"); you may not use this file except in
@@ -1682,7 +1682,7 @@ smp_select0(Config) ->
     ProcFun = fun()-> io:format("Worker ~p starting\n",[self()]),	
 		      ?line Port = open_port({spawn, DrvName}, []),
 		      smp_select_loop(Port, 100000),
-		      sleep(500), % wait for driver to handle pending events
+		      sleep(1000), % wait for driver to handle pending events
 		      ?line true = erlang:port_close(Port),
 		      Master ! {ok,self()},
 		      io:format("Worker ~p finished\n",[self()])
diff --git a/erts/emulator/test/driver_SUITE_data/chkio_drv.c b/erts/emulator/test/driver_SUITE_data/chkio_drv.c
index b571cb30e6..bbdb09cfcb 100644
--- a/erts/emulator/test/driver_SUITE_data/chkio_drv.c
+++ b/erts/emulator/test/driver_SUITE_data/chkio_drv.c
@@ -102,6 +102,7 @@ typedef struct chkio_smp_select {
     int write_fd;
     int next_read;
     int next_write;
+    int first_write;
     enum {Closed, Opened, Selected, Waiting} state;
     int wasSelected;
     unsigned rand_state;
@@ -577,9 +578,16 @@ chkio_drv_ready_input(ErlDrvData drv_data, ErlDrvEvent event)
 	inPipe = (pip->next_write - pip->next_read);
 	if (inPipe == 0) {
 	    bytes = read(pip->read_fd, &word, sizeof(word));
-	    printf("Unexpected empty pipe, expected %u -> %u, bytes=%d, word=%d\n",
-		   pip->next_read, pip->next_write-1, bytes, word);
-	    abort();
+	    printf("Unexpected empty pipe, expected %u -> %u, bytes=%d, word=%d, written=%d\n",
+		   pip->next_read, pip->next_write-1, bytes, word,
+		   (pip->next_write - pip->first_write));
+	    /*abort();
+    	      Allow unexpected events as it's been seen to be triggered by epoll
+	      on Linux. Most of the time the unwanted events are filtered by
+	      the erl_check_io layer. But when fd's are reused the events may
+	      slip up to the driver.
+	    */
+	    break; 
 	}
 
 	n = rand_r(&pip->rand_state) % (inPipe*4);
@@ -1252,6 +1260,7 @@ chkio_drv_control(ErlDrvData drv_data,
 		pip->state = Opened;
 		pip->wasSelected = 0;
 		pip->next_write = pip->next_read = rand_r(&pip->rand_state) % 1024;
+		pip->first_write = pip->next_write;
 		if (op & 1) break;
 		op >>= 1;
 	    }/*fall through*/