[ python-Bugs-1423153 ] mmap module leaks file descriptors on UNIX

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Bugs item #1423153, was opened at 2006-02-02 18:25
Message generated for change (Comment added) made by kdart
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Category: Extension Modules
Group: Python 2.4
Status: Open
Resolution: None
Priority: 5
Submitted By: Fazal Majid (majid)
Assigned to: Nobody/Anonymous (nobody)
Summary: mmap module leaks file descriptors on UNIX

Initial Comment:
On UNIX, mmapmodule.c makes a call to dup(2) prior to
mapping the file descriptor into memory (oddly enough,
it doesn't map the new fd resulting from dup(), but the
old one).

The close method does not release this file descriptor,
however, leading to a leak. If mmap is used repeatedly,
the process will eventually run out of file
descriptors, as can easily be shown with this test case:

import sys, os, mmap

for i in xrange(2000):
  f = os.open('/dev/zero', os.O_RDWR)
  m = mmap.mmap(f, 10000)
  os.close(f)
  a = m[0:100]
  m[100:200] = 'F' * 100
  m.close()


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Comment By: Keith Dart (kdart)
Date: 2006-02-03 06:51

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I would also like to add that the following no longer works
in Python 2.4:

_buf = mmap.mmap(-1, 8192,
flags=mmap.MAP_PRIVATE|mmap.MAP_ANONYMOUS,
prot=mmap.PROT_READ|mmap.PROT_WRITE )

This is because the fd value of -1 raises an exception
because it is being dup-ed inside the mmap module. But the
fd is ignored in anonymous mmaps and does not need to be
dup-ed. This worked in older Python (2.3). Is the dup() call
really necessary?


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Comment By: Fazal Majid (majid)
Date: 2006-02-02 18:44

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The following patch closes the file descriptor when the mmap
object's close method is called, and seems to resolve this
problem.

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Comment By: Fazal Majid (majid)
Date: 2006-02-02 18:27

Message:
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SourceForge munged the formatting of the test case, so I am
attaching a copy as well.

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