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Fixes issue1336 - a race condition could occur when forking if the gc 

kicked in during the critical section.  solution: disable gc during
that section.  Patch contributed by jpa and updated by me to cover the
race condition still existing what therve from twistedmatrix pointed
out (already seen and fixed in twisted's own subprocess code).
This commit is contained in:
Gregory P. Smith 2008-01-19 20:57:59 +00:00
parent f558d2e5f5
commit 87d49792b5
1 changed files with 63 additions and 50 deletions
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113
Lib/subprocess.py
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@ -356,6 +356,7 @@ mswindows = (sys.platform == "win32")
import os import os
import types import types
import traceback import traceback
import gc
# Exception classes used by this module. # Exception classes used by this module.
class CalledProcessError(Exception): class CalledProcessError(Exception):
@ -994,66 +995,78 @@ class Popen(object):
errpipe_read, errpipe_write = os.pipe() errpipe_read, errpipe_write = os.pipe()
self._set_cloexec_flag(errpipe_write) self._set_cloexec_flag(errpipe_write)
self.pid = os.fork() gc_was_enabled = gc.isenabled()
self._child_created = True # Disable gc to avoid bug where gc -> file_dealloc ->
if self.pid == 0: # write to stderr -> hang. http://bugs.python.org/issue1336
# Child gc.disable()
try: try:
# Close parent's pipe ends self.pid = os.fork()
if p2cwrite is not None: except:
os.close(p2cwrite) if gc_was_enabled:
if c2pread is not None: gc.enable()
os.close(c2pread) raise
if errread is not None: else:
os.close(errread) self._child_created = True
os.close(errpipe_read) if self.pid == 0:
# Child
try:
# Close parent's pipe ends
if p2cwrite is not None:
os.close(p2cwrite)
if c2pread is not None:
os.close(c2pread)
if errread is not None:
os.close(errread)
os.close(errpipe_read)
# Dup fds for child # Dup fds for child
if p2cread is not None: if p2cread is not None:
os.dup2(p2cread, 0) os.dup2(p2cread, 0)
if c2pwrite is not None: if c2pwrite is not None:
os.dup2(c2pwrite, 1) os.dup2(c2pwrite, 1)
if errwrite is not None: if errwrite is not None:
os.dup2(errwrite, 2) os.dup2(errwrite, 2)
# Close pipe fds. Make sure we don't close the same # Close pipe fds. Make sure we don't close the same
# fd more than once, or standard fds. # fd more than once, or standard fds.
if p2cread is not None and p2cread not in (0,): if p2cread is not None and p2cread not in (0,):
os.close(p2cread) os.close(p2cread)
if c2pwrite is not None and c2pwrite not in (p2cread, 1): if c2pwrite is not None and c2pwrite not in (p2cread, 1):
os.close(c2pwrite) os.close(c2pwrite)
if errwrite is not None and errwrite not in (p2cread, c2pwrite, 2): if errwrite is not None and errwrite not in (p2cread, c2pwrite, 2):
os.close(errwrite) os.close(errwrite)
# Close all other fds, if asked for # Close all other fds, if asked for
if close_fds: if close_fds:
self._close_fds(but=errpipe_write) self._close_fds(but=errpipe_write)
if cwd is not None: if cwd is not None:
os.chdir(cwd) os.chdir(cwd)
if preexec_fn: if preexec_fn:
apply(preexec_fn) apply(preexec_fn)
if env is None: if env is None:
os.execvp(executable, args) os.execvp(executable, args)
else: else:
os.execvpe(executable, args, env) os.execvpe(executable, args, env)
except: except:
exc_type, exc_value, tb = sys.exc_info() exc_type, exc_value, tb = sys.exc_info()
# Save the traceback and attach it to the exception object # Save the traceback and attach it to the exception object
exc_lines = traceback.format_exception(exc_type, exc_lines = traceback.format_exception(exc_type,
exc_value, exc_value,
tb) tb)
exc_value.child_traceback = ''.join(exc_lines) exc_value.child_traceback = ''.join(exc_lines)
os.write(errpipe_write, pickle.dumps(exc_value)) os.write(errpipe_write, pickle.dumps(exc_value))
# This exitcode won't be reported to applications, so it # This exitcode won't be reported to applications, so it
# really doesn't matter what we return. # really doesn't matter what we return.
os._exit(255) os._exit(255)
# Parent # Parent
if gc_was_enabled:
gc.enable()
os.close(errpipe_write) os.close(errpipe_write)
if p2cread is not None and p2cwrite is not None: if p2cread is not None and p2cwrite is not None:
os.close(p2cread) os.close(p2cread)