Gregory P. Smith added the comment:
There appear to be a two bugs here, depending on which platform subprocess is
being used on.
1) on systems where it uses /prod/self/fd, /dev/fd or similar:
It should not pay attention to end_fd at all. It knows the list of actual
open fds and should use that. If possible, consider detecting and avoiding
closing valgrind fds; but that is a special case for a valgrind bug and likely
not worth it.
2) on systems without a way to get the list of open file descriptors:
The sysconf("SC_OPEN_MAX") value is only saved at module import time but may
be changed up or down at runtime by the process by using the
setrlimit(RLIMIT_NOFILE, ...) libc call. what sysconf returns is the same as
the current rlim_cur setting. (at least on Linux where this code path wouldn't
actually be taken because #1 is available).
possible solution: call getrlimit(RLIMIT_NOFILE) and use rlim_max instead of
sysconf("SC_OPEN_MAX") at module import time.
caveat: rlim_max can be raised by processes granted that capbility. It is
impossible to do anything about that in this scenario given we're operating w/o
a way to get a list of open fds.
impact: only on OSes that lack implementations that get a list of open fds as
in #1 above. so... nothing that anyone really uses unless they choose to come
contribute support for that themselves. (linux, bsd and os x all fall into #1
above)
Neither of these are likely scenarios so I wouldn't consider this a high
priority to fix but it should be done. Most code never ever touches its os
resource limits. getrlimit and setrlimit are not exposed in the os module; you
must use ctypes or an extension module to call them from Python:
import ctypes
class StructRLimit(ctypes.Structure):
_fields_ = [('rlim_cur', ctypes.c_ulong), ('rlim_max', ctypes.c_ulong)]
libc = ctypes.cdll.LoadLibrary('libc.so.6')
RLIMIT_NOFILE = 7 # Linux
limits = StructRLimit()
assert libc.getrlimit(RLIMIT_NOFILE, ctypes.byref(limits)) == 0
print(limits.rlim_cur, limits.rlim_max)
limits.rlim_cur = limits.rlim_max
assert libc.setrlimit(RLIMIT_NOFILE, ctypes.byref(limits)) == 0
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<http://bugs.python.org/issue21618>
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