OSError: [Errno 10] No child processes

[yonas]

BPO	6122
Nosy	@amauryfa, @florentx
Superseder	bpo-1731717: race condition in subprocess module
Files	mylib.c main.c exim_local_scan2.py

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2010-03-04.22:58:08.380>
created_at = <Date 2009-05-27.08:12:14.733>
labels = ['type-bug', 'library']
title = 'OSError: [Errno 10] No child processes'
updated_at = <Date 2010-03-04.22:58:08.378>
user = 'https://bugs.python.org/yonas'

bugs.python.org fields:

activity = <Date 2010-03-04.22:58:08.378>
actor = 'flox'
assignee = 'none'
closed = True
closed_date = <Date 2010-03-04.22:58:08.380>
closer = 'flox'
components = ['Library (Lib)']
creation = <Date 2009-05-27.08:12:14.733>
creator = 'yonas'
dependencies = []
files = ['14088', '14089', '14094']
hgrepos = []
issue_num = 6122
keywords = []
message_count = 10.0
messages = ['88407', '88408', '88422', '88423', '88424', '88426', '88433', '88440', '88442', '100431']
nosy_count = 3.0
nosy_names = ['amaury.forgeotdarc', 'yonas', 'flox']
pr_nums = []
priority = 'normal'
resolution = 'duplicate'
stage = None
status = 'closed'
superseder = '1731717'
type = 'behavior'
url = 'https://bugs.python.org/issue6122'
versions = ['Python 2.6', 'Python 2.5', 'Python 3.0']

[yonas]

I always get a subprocess error when using embedded Python 2.6.2:

File "/usr/lib/python2.6/subprocess.py", line 1123, in wait: pid,
sts = os.waitpid(self.pid, 0): OSError: [Errno 10] No child processes

Sample library and main files attached.

[amauryfa]

The content of exim_local_scan2.py would be useful as well.

[yonas]

The test doesn't fail when run directly from ./main, but it fails when
run from exim4 mail server.

exim will dlopen() mylib and run local_scan().

Besides using Popen, I haven't had any problems.

[amauryfa]

your program works for me.
How did you compile the files? I used the following commands:

$ gcc -fPIC -I/usr/local/include/python2.6/ mylib.c -L /usr/local/lib
-lpython2.6 --shared -o mylib.so

$ gcc main.c -ldl 

$ ./a.out
test

(after removing all references to exim4, which is not really used)

[yonas]

Thanks for testing, it works when running ./main, but not when run
through exim.

[yonas]

I didn't find anything unusual about how exim uses dlopen, but if you
want to see the code, it's here:

http://pastebin.com/m52398b30

Line 166 is the actual call.

Again, no problems except with Python's Popen().

[yonas]

Could this be a permissions issue? I have no idea how permissions would
effect it, though...

root@yonas-laptop:/usr/lib/exim4/local_scan# ls -la /usr/sbin/exim4
-rwsr-xr-x 1 root root 824440 2009-02-11 08:53 /usr/sbin/exim4

[yonas]

os.system() works:

os.system("echo `date` >> /tmp/myfile")

root@yonas-laptop:/usr/lib/exim4/local_scan# cat /tmp/myfile
Wed May 27 16:04:54 EDT 2009
Wed May 27 16:04:54 EDT 2009

[yonas]

Here's another test, taken from the docs:

http://docs.python.org/library/subprocess.html#subprocess-replacements:

This is slightly better than Popen because the program executes and
shows output, but worse than os.system(), because it still shows the error:

--------------------------
try:
retcode = call("echo" + " \"hello world\"", shell=True)
if retcode < 0:
print >>sys.stderr, "Child was terminated by signal",
-retcode
print >>sys.stderr, "Child was terminated by signal",
-retcode
else:
print >>sys.stderr, "Child returned", retcode
except OSError, e:
print >>sys.stderr, "Execution failed:", e

-----------------
hello world
Execution failed: [Errno 10] No child processes

[florentx]

Another duplicate of bpo-1731717