Re: Problem with gnuplot backend + popen2 + non-blocking mode

[John W. Eaton]

On 24-Apr-2008, Michael Goffioul wrote:

| On Thu, Apr 24, 2008 at 7:29 PM, John W. Eaton <address@hidden> wrote:
| >  I would have expected the pipe that is open for writing to already be
| >  in blocking-write mode.  Here is what I see:
| >
| >   octave:1>   [to_gnuplot, from_gnuplot] = popen2 ("gnuplot")
| >   in =  4
| >   out =  5
| >   octave:2>   bitand (fcntl (to_gnuplot, F_GETFL, 0), O_NONBLOCK)
| >   ans = 0
| >   octave:3>   bitand (fcntl (from_gnuplot, F_GETFL, 0), O_NONBLOCK)
| >   ans =  2048
| >
| >  Do you also see a non-zero result for the "to_gp" stream?  If so, then
| >  does the following patch fix the problem?
| 
| I didn't check, but I'm pretty sure it won't change anything
| as fcntl does not work under Win32;
| 
| >  Instead of fixing the problem in gnuplot_drawnow, maybe the
| >  octave_popen2 function for Windows should be fixed to open the writing
| >  stream in blocking mode, same as the Unixy popen2 does?
| 
| Indeed. I didn't realize that the sync_mode flag only controlled
| the read pipe, while the write pipe was always in blocking mode.
| The Windows version of popen2 does not do that, it puts both
| pipes in non-blocking mode.
| 
| Do you want me to propose a patch? Or would you do it
| yourself? (it's a only one line to remove, in lo-sysdep.cc,
| around line 143; the SetNamedPipeHandleState call for
| parentWrite should be removed).

I checked in the following change.  Is that OK?

Thanks,

jwe

# HG changeset patch
# User Michael Goffioul
# Date 1209066081 14400
# Node ID c0d3ecb30f4ba38749b9ccd2a322db0eb6832651
# Parent  2d2a969c731ca25a53191f3d428ebe1c2e818b4f
lo-sysdep.cc (octave_popen2): don't set PIPE_NOWAIT for parentWrite

diff --git a/liboctave/ChangeLog b/liboctave/ChangeLog
--- a/liboctave/ChangeLog
+++ b/liboctave/ChangeLog
@@ -1,3 +1,7 @@ 2008-04-21  John W. Eaton  <address@hidden
+2008-04-24  Michael Goffioul  <address@hidden>
+
+       * lo-sysdep.cc (octave_popen2): Don't set PIPE_NOWAIT for parentWrite.
+
 2008-04-21  John W. Eaton  <address@hidden>
 
        * idx-vector.cc (IDX_VEC_REP::idx_vector_rep (const boolNDArray&)):
diff --git a/liboctave/lo-sysdep.cc b/liboctave/lo-sysdep.cc
--- a/liboctave/lo-sysdep.cc
+++ b/liboctave/lo-sysdep.cc
@@ -141,7 +141,6 @@ octave_popen2 (const std::string& cmd, c
     {
       pipeMode = PIPE_NOWAIT;
       SetNamedPipeHandleState (parentRead, &pipeMode, 0, 0);
-      SetNamedPipeHandleState (parentWrite, &pipeMode, 0, 0);
     }
   fildes[1] = _open_osfhandle (reinterpret_cast<long> (parentRead), _O_RDONLY 
| _O_BINARY);
   fildes[0] = _open_osfhandle (reinterpret_cast<long> (parentWrite), _O_WRONLY 
| _O_BINARY);
diff --git a/scripts/plot/gnuplot_drawnow.m b/scripts/plot/gnuplot_drawnow.m
--- a/scripts/plot/gnuplot_drawnow.m
+++ b/scripts/plot/gnuplot_drawnow.m
@@ -78,6 +78,12 @@ function [plot_stream, enhanced] = open_
     [plot_stream(1), plot_stream(2), pid] = popen2 (cmd);
     if (pid < 0)
       error ("drawnow: failed to open connection to gnuplot");
+    else
+      ## Ensure that the stream open from writing to gnuplot is in
+      ## blocking-write mode:
+      oflags = fcntl (plot_stream(1), F_GETFL, 0);
+      nflags = bitand (oflags, bitcmp (O_NONBLOCK));
+      fcntl (plot_stream(1), F_SETFL, nflags);
     endif
   else
     plot_stream = popen (cmd, "w");