Commit eef54f46 authored by Jason Madden's avatar Jason Madden Committed by GitHub

Merge pull request #858 from gevent/double-subproc

Allow resetting the C state for whether libev child handlers are active.
parents e2eb3e09 a1fa3e12
......@@ -90,6 +90,16 @@ Stdlib Compatibility
returning the errno due to the refactoring of the exception
hierarchy in Python 3.3. Now the errno is returned. Reported in
:issue:`841` by Dana Powers.
- Setting SIGCHLD to SIG_IGN or SIG_DFL after :mod:`gevent.subprocess`
had been used previously could not be reversed, causing
``Popen.wait`` and other calls to hang. Now, if SIGCHLD has been
ignored, the next time :mod:`gevent.subprocess` is used this will be
detected and corrected automatically. (This potentially leads to
issues with :func:`os.popen` on Python 2, but the signal can always
be reset again. Mixing the low-level process handling calls,
low-level signal management and high-level use of
:mod:`gevent.subprocess` is tricky.) Reported in :issue:`857` by
Chris Utz.
Other Changes
-------------
......
......@@ -206,6 +206,7 @@ unsigned int ev_pending_count(struct ev_loop*);
struct ev_loop* gevent_ev_default_loop(unsigned int flags);
void gevent_install_sigchld_handler();
void gevent_reset_sigchld_handler();
void (*gevent_noop)(struct ev_loop *_loop, struct ev_timer *w, int revents);
void ev_sleep (ev_tstamp delay); /* sleep for a while */
......
......@@ -504,6 +504,9 @@ cdef public class loop [object PyGeventLoopObject, type PyGeventLoop_Type]:
def install_sigchld(self):
libev.gevent_install_sigchld_handler()
def reset_sigchld(self):
libev.gevent_reset_sigchld_handler()
#endif
def stat(self, str path, float interval=0.0, ref=True, priority=None):
......
......@@ -608,6 +608,9 @@ class loop(object):
def install_sigchld(self):
libev.gevent_install_sigchld_handler()
def reset_sigchld(self):
libev.gevent_reset_sigchld_handler()
def stat(self, path, interval=0.0, ref=True, priority=None):
return stat(self, path, interval, ref, priority)
......
......@@ -12,6 +12,14 @@
#ifndef _WIN32
static struct sigaction libev_sigchld;
/*
* Track the state of whether we have installed
* the libev sigchld handler specifically.
* If it's non-zero, libev_sigchld will be valid and set to the action
* that libev needs to do.
* If it's 1, we need to install libev_sigchld to make libev
* child handlers work (on request).
*/
static int sigchld_state = 0;
static struct ev_loop* gevent_ev_default_loop(unsigned int flags)
......@@ -22,9 +30,12 @@ static struct ev_loop* gevent_ev_default_loop(unsigned int flags)
if (sigchld_state)
return ev_default_loop(flags);
// Request the old SIGCHLD handler
sigaction(SIGCHLD, NULL, &tmp);
// Get the loop, which will install a SIGCHLD handler
result = ev_default_loop(flags);
// XXX what if SIGCHLD received there?
// Now restore the previous SIGCHLD handler
sigaction(SIGCHLD, &tmp, &libev_sigchld);
sigchld_state = 1;
return result;
......@@ -38,6 +49,15 @@ static void gevent_install_sigchld_handler(void) {
}
}
static void gevent_reset_sigchld_handler(void) {
// We could have any state at this point, depending on
// whether the default loop has been used. If it has,
// then always be in state 1 ("need to install)
if (sigchld_state) {
sigchld_state = 1;
}
}
#else
#define gevent_ev_default_loop ev_default_loop
......
......@@ -205,3 +205,4 @@ cdef extern from "libev.h":
ev_loop* gevent_ev_default_loop(unsigned int flags)
void gevent_install_sigchld_handler()
void gevent_reset_sigchld_handler()
......@@ -15,6 +15,7 @@ information on configuring this not to be the case for advanced uses.
"""
from __future__ import absolute_import
from gevent._util import _NONE as _INITIAL
from gevent._util import copy_globals
......@@ -34,6 +35,9 @@ def getsignal(signalnum):
"""
Exactly the same as :func:`signal.signal` except where
:const:`signal.SIGCHLD` is concerned.
For :const:`signal.SIGCHLD`, this cooperates with :func:`signal`
to provide consistent answers.
"""
if signalnum != _signal.SIGCHLD:
return _signal_getsignal(signalnum)
......@@ -67,9 +71,16 @@ def signal(signalnum, handler):
Use of ``SIG_IGN`` and ``SIG_DFL`` may also have race conditions
with libev child watchers and the :mod:`gevent.subprocess` module.
.. versionchanged:: 1.2a1
If ``SIG_IGN`` or ``SIG_DFL`` are used to ignore ``SIGCHLD``, a
future use of ``gevent.subprocess`` and libev child watchers
will once again work. However, on Python 2, use of ``os.popen``
will fail.
.. versionchanged:: 1.1rc2
Allow using ``SIG_IGN`` and ``SIG_DFL`` to reset and ignore ``SIGCHLD``.
However, this allows the possibility of a race condition.
Allow using ``SIG_IGN`` and ``SIG_DFL`` to reset and ignore ``SIGCHLD``.
However, this allows the possibility of a race condition if ``gevent.subprocess``
had already been used.
"""
if signalnum != _signal.SIGCHLD:
return _signal_signal(signalnum, handler)
......@@ -87,8 +98,11 @@ def signal(signalnum, handler):
if handler == _signal.SIG_IGN or handler == _signal.SIG_DFL:
# Allow resetting/ignoring this signal at the process level.
# Note that this conflicts with gevent.subprocess and other users
# of child watchers.
# of child watchers, until the next time gevent.subprocess/loop.install_sigchld()
# is called.
from gevent import get_hub # Are we always safe to import here?
_signal_signal(signalnum, handler)
get_hub().loop.reset_sigchld()
return old_handler
......
# Mimics what gunicorn workers do *if* the arbiter is also monkey-patched:
# After forking from the master monkey-patched process, the child
# resets signal handlers to SIG_DFL. If we then fork and watch *again*,
# we shouldn't hang. (Note that we carefully handle this so as not to break
# os.popen)
from __future__ import print_function
# Patch in the parent process.
import gevent.monkey
gevent.monkey.patch_all()
from gevent import get_hub
import os
import sys
import signal
import subprocess
def _waitpid(pid):
try:
_, stat = os.waitpid(pid, 0)
except OSError:
# Interrupted system call
_, stat = os.waitpid(pid, 0)
assert stat == 0, stat
if hasattr(signal, 'SIGCHLD'):
# Do what subprocess does and make sure we have the watcher
# in the parent
get_hub().loop.install_sigchld()
pid = os.fork()
if pid: # parent
_waitpid(pid)
else:
# Child resets.
signal.signal(signal.SIGCHLD, signal.SIG_DFL)
# Go through subprocess because we expect it to automatically
# set up the waiting for us.
popen = subprocess.Popen([sys.executable, '-c', 'import sys'],
stdout=subprocess.PIPE, stderr=subprocess.PIPE)
popen.stderr.read()
popen.stdout.read()
popen.wait() # This hangs if it doesn't.
sys.exit(0)
else:
print("No SIGCHLD, not testing")
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