[issue11284] slow close file descriptors in subprocess, popen2, os.popen*

[Charles-Francois Natali]

Charles-Francois Natali <neologix at free.fr> added the comment:

Attached is a patch adding os.closefrom.
If closefrom(2) is available, it's used.
Otherwise, two options:
- if sysconf and _SC_OPEN_MAX are defined, we close each file descriptor up to _SC_OPEN_MAX
- if not, we choose a default value (256), and close every FD up to this value
subprocess has been converted to use it, and a test has been added in test_os
Unfortunately, I only have Linux boxes, so I can't really test it.

Remarks:
- is it OK to provide posix_closefrom even though the underlying platform doesn't support it ?
- no error code is returned (since when closing every FD manually this wouldn't make much sense), even though closefrom(2) does return one
- for the test, I only close FDs > 7 to avoid closing stdin/stdout/stder, but you might have a better idea
- this won't fix the problem for Linux, which doesn't have closefrom(2). Is it worth using /proc/self/fd interface ?

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Added file: http://bugs.python.org/file20979/py3k_closefrom.diff

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