[Octave-bug-tracker] [bug #48149] popen2 on Windows requires delay

[Rik]

URL:
  <http://savannah.gnu.org/bugs/?48149>

                 Summary: popen2 on Windows requires delay
                 Project: GNU Octave
            Submitted by: rik5
            Submitted on: Mon 06 Jun 2016 09:02:22 AM PDT
                Category: Octave Function
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Incorrect Result
                  Status: None
             Assigned to: None
         Originator Name: 
        Originator Email: 
             Open/Closed: Open
         Discussion Lock: Any
                 Release: dev
        Operating System: Microsoft Windows

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Details:

There is example code in the docstring for popen2.  The code is


[in, out, pid] = popen2 ("sort", "-r");
fputs (in, "these\nare\nsome\nstrings\n");
fclose (in);
EAGAIN = errno ("EAGAIN");
done = false;
do
  s = fgets (out);
  if (ischar (s))
    fputs (stdout, s);
  elseif (errno () == EAGAIN)
    pause (0.1);
    fclear (out);
  else
    done = true;
  endif
until (done)
fclose (out);
waitpid (pid);


This works correctly on Linux, but fails on Windows.  The problem is that the
initial call to fgets (out) returns -1 (EOF) immediately.  I can get the code
to work by adding a small delay before starting the do loop.

This works


[in, out, pid] = popen2 ("sort", "-r");
fputs (in, "these\nare\nsome\nstrings\n");
fclose (in);
EAGAIN = errno ("EAGAIN");
done = false;
pause (0.05);  # 50 millisecond pause
do
  s = fgets (out);
  if (ischar (s))
    fputs (stdout, s);
  elseif (errno () == EAGAIN)
    pause (0.1);
    fclear (out);
  else
    done = true;
  endif
until (done)
fclose (out);
waitpid (pid);


I tried using fflush (in) before fclose, but that didn't help.  The problem is
either in the popen2 call, which is Windows specific and located in
liboctave/system/lo-sysdep.cc.  Or Windows itself has problems with
concurrency.

I've attached the test code to this bug report.




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File Attachments:


-------------------------------------------------------
Date: Mon 06 Jun 2016 09:02:22 AM PDT  Name: tst_popen2.m  Size: 339B   By:
rik5

<http://savannah.gnu.org/bugs/download.php?file_id=37409>

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