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"""
Cooperative implementation of special cases of :func:`signal.signal`.
This module is designed to work with libev's child watchers, as used
by default in :func:`gevent.os.fork` Note that each ``SIGCHLD`` handler
will be run in a new greenlet when the signal is delivered (just like
:class:`gevent.hub.signal`)
The implementations in this module are only monkey patched if
:func:`gevent.os.waitpid` is being used (the default) and if
:const:`signal.SIGCHLD` is available; see :func:`gevent.os.fork` for
information on configuring this not to be the case for advanced uses.
.. versionadded:: 1.1b4
"""
from __future__ import absolute_import
from gevent._util import _NONE as _INITIAL
from gevent._util import copy_globals
import signal as _signal
__implements__ = []
__extensions__ = []
_child_handler = _INITIAL
_signal_signal = _signal.signal
_signal_getsignal = _signal.getsignal
def getsignal(signalnum):
"""
Exactly the same as :func:`signal.getsignal` 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)
global _child_handler
if _child_handler is _INITIAL:
_child_handler = _signal_getsignal(_signal.SIGCHLD)
return _child_handler
def signal(signalnum, handler):
"""
Exactly the same as :func:`signal.signal` except where
:const:`signal.SIGCHLD` is concerned.
.. note::
A :const:`signal.SIGCHLD` handler installed with this function
will only be triggered for children that are forked using
:func:`gevent.os.fork` (:func:`gevent.os.fork_and_watch`);
children forked before monkey patching, or otherwise by the raw
:func:`os.fork`, will not trigger the handler installed by this
function. (It's unlikely that a SIGCHLD handler installed with
the builtin :func:`signal.signal` would be triggered either;
libev typically overwrites such a handler at the C level. At
the very least, it's full of race conditions.)
.. note::
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 if ``gevent.subprocess``
had already been used.
"""
if signalnum != _signal.SIGCHLD:
return _signal_signal(signalnum, handler)
# TODO: raise value error if not called from the main
# greenlet, just like threads
if handler != _signal.SIG_IGN and handler != _signal.SIG_DFL and not callable(handler):
# exact same error message raised by the stdlib
raise TypeError("signal handler must be signal.SIG_IGN, signal.SIG_DFL, or a callable object")
old_handler = getsignal(signalnum)
global _child_handler
_child_handler = handler
if handler in (_signal.SIG_IGN, _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, until the next time gevent.subprocess/loop.install_sigchld()
# is called.
from gevent.hub import get_hub # Are we always safe to import here?
_signal_signal(signalnum, handler)
get_hub().loop.reset_sigchld()
return old_handler
def _on_child_hook():
# This is called in the hub greenlet. To let the function
# do more useful work, like use blocking functions,
# we run it in a new greenlet; see gevent.hub.signal
if callable(_child_handler):
# None is a valid value for the frame argument
from gevent import Greenlet
greenlet = Greenlet(_child_handler, _signal.SIGCHLD, None)
greenlet.switch()
import gevent.os
if 'waitpid' in gevent.os.__implements__ and hasattr(_signal, 'SIGCHLD'):
# Tightly coupled here to gevent.os and its waitpid implementation; only use these
# if necessary.
gevent.os._on_child_hook = _on_child_hook
__implements__.append("signal")
__implements__.append("getsignal")
else:
# XXX: This breaks test__all__ on windows
__extensions__.append("signal")
__extensions__.append("getsignal")
__imports__ = copy_globals(_signal, globals(),
names_to_ignore=__implements__ + __extensions__,
dunder_names_to_keep=())
__all__ = __implements__ + __extensions__