Source code for gevent.signal

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
.. versionchanged:: 1.5a4
   Previously there was a backwards compatibility alias
   ``gevent.signal``, introduced in 1.1b4, that partly shadowed this
   module, confusing humans and static analysis tools alike. That alias
   has been removed. (See `gevent.signal_handler`.)

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

[docs]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
[docs]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__