popen2.Popen3 process destruction

Donn Cave donn at u.washington.edu
Wed Jun 16 00:35:16 CEST 2004

In article <mailman.9.1087331026.21521.python-list at python.org>,
 <brianc at temple.edu> wrote:

> I have created a class which inherits popen2.Popen3. 
> The problem is that popen2.Popen3 does not define a __del__
> method to handle proper closing of the pipes or destruction of
> the process. So I created one in my class:
> However, since the popen2 module stores a reference to the
> object in popen2._active this __del__ method is never called
> to clean things up. _cleanup() called in Popen3.__init__()
> fails to clean up the process in subsequent instantiations.
> This eventually leads to an "OSError: [Errno 24] Too many open
> files"

The instance needs to keep itself around, to work with popen2
and popen3 functions and generally support direct use of the
pipe fileobjects and file descriptors.

> "_clean()" fails because the program being called is
> interactive using stdin/stdout. Much in the way "cat" is. In
> fact the unit test provided with the popen2 module _test()
> uses "cat" and hangs for the very same reason. It hangs on
> "for inst in _active[:]:inst.wait()" This is why I created my
> own class, to handle this special interactive nature.

That is not normal, that I know of - test_open2.py's use
of cat should not cause a hang.  Unless we're looking at
very different versions of test_popen2.py.  I wonder if
there could be a problem somewhere in the IRIX64
implementation of Python, or in the OS itself.

   Donn Cave, donn at u.washington.edu

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