Message125067
There is an issue where if a python program closes all the std. file descriptors (e.g. a daemon) and then uses the subprocess module, the file descriptors may not be set up properly in the subprocess. This may actually be a fairly common use case in a daemon program that needs to run a subprocess and set up pipes to it.
Here is an example:
import os, subprocess, sys
x=os.open('/dev/null', os.O_RDWR)
os.close(0)
os.close(1)
os.close(2)
res = subprocess.Popen([sys.executable, "-c",
'import sys;'
'sys.stdout.write("apple");'
'sys.stdout.flush();'
'sys.stderr.write("orange")'],
stdin=x,
stdout=subprocess.PIPE,
stderr=subprocess.PIPE).communicate()
with open('/tmp/out', 'w') as f:
f.write(repr(res) + '\n')
f.write(repr((b'apple', b'orange')) + '\n')
The expected output in /tmp/out is:
('apple', 'orange')
('apple', 'orange')
but we get:
(b'', b"Fatal Python error: Py_Initialize: can't initialize sys standard streams\nOSError: [Errno 9] Bad file descriptor\n")
(b'apple', b'orange')
The problem comes about where the calls are made (this applies to the python & c versions):
os.dup2(p2cread, 0)
os.dup2(c2pwrite, 1)
os.dup2(errwrite, 2)
if c2pwrite or p2cread or errwrite is the same as what it's being dupped() to (eg if c2pwrite == 1) then the dup2 call does nothing. But, if we're using pipes, the close-on-exec flags are set initially and the dup2() call would normally remove the flag but it doesn't.
Attached is a patch which basically uses fcntl if necessary to remove the close-on-exec flag, and tests. |
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Date |
User |
Action |
Args |
2011-01-02 18:08:37 | rosslagerwall | set | recipients:
+ rosslagerwall, georg.brandl, gregory.p.smith, pitrou, giampaolo.rodola |
2011-01-02 18:08:37 | rosslagerwall | set | messageid: <1293991717.46.0.660046429073.issue10806@psf.upfronthosting.co.za> |
2011-01-02 18:08:35 | rosslagerwall | link | issue10806 messages |
2011-01-02 18:08:35 | rosslagerwall | create | |
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