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# Copyright (C) 2011 Canonical Ltd
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
"""Signal handling for the smart server code."""
from __future__ import absolute_import
import signal
import weakref
from bzrlib import trace
# I'm pretty sure this has to be global, since signal handling is per-process.
_on_sighup = None
# TODO: Using a dict means that the order of calls is unordered. We could use a
# list and then do something like LIFO ordering. A dict was chosen so
# that you could have a key to easily remove your entry. However, you
# could just use the callable itself as the indexed part, and even in
# large cases, we shouldn't have more than 100 or so callbacks
# registered.
def _sighup_handler(signal_number, interrupted_frame):
"""This is the actual function that is registered for handling SIGHUP.
It will call out to all the registered functions, letting them know that a
graceful termination has been requested.
"""
if _on_sighup is None:
return
trace.mutter('Caught SIGHUP, sending graceful shutdown requests.')
for ref in _on_sighup.valuerefs():
try:
cb = ref()
if cb is not None:
cb()
except KeyboardInterrupt:
raise
except Exception:
trace.mutter('Error occurred while running SIGHUP handlers:')
trace.log_exception_quietly()
def install_sighup_handler():
"""Setup a handler for the SIGHUP signal."""
if getattr(signal, "SIGHUP", None) is None:
# If we can't install SIGHUP, there is no reason (yet) to do graceful
# shutdown.
old_signal = None
else:
old_signal = signal.signal(signal.SIGHUP, _sighup_handler)
old_dict = _setup_on_hangup_dict()
return old_signal, old_dict
def _setup_on_hangup_dict():
"""Create something for _on_sighup.
This is done when we install the sighup handler, and for tests that want to
test the functionality. If this hasn'nt been called, then
register_on_hangup is a no-op. As is unregister_on_hangup.
"""
global _on_sighup
old = _on_sighup
_on_sighup = weakref.WeakValueDictionary()
return old
def restore_sighup_handler(orig):
"""Pass in the returned value from install_sighup_handler to reset."""
global _on_sighup
old_signal, old_dict = orig
if old_signal is not None:
signal.signal(signal.SIGHUP, old_signal)
_on_sighup = old_dict
# TODO: Should these be single-use callables? Meaning that once we've triggered
# SIGHUP and called them, they should auto-remove themselves? I don't
# think so. Callers need to clean up during shutdown anyway, so that we
# don't end up with lots of garbage in the _on_sighup dict. On the other
# hand, we made _on_sighup a WeakValueDictionary in case cleanups didn't
# get fired properly. Maybe we just assume we don't have to do it?
def register_on_hangup(identifier, a_callable):
"""Register for us to call a_callable as part of a graceful shutdown."""
if _on_sighup is None:
return
_on_sighup[identifier] = a_callable
def unregister_on_hangup(identifier):
"""Remove a callback from being called during sighup."""
if _on_sighup is None:
return
try:
del _on_sighup[identifier]
except KeyboardInterrupt:
raise
except Exception:
# This usually runs as a tear-down step. So we don't want to propagate
# most exceptions.
trace.mutter('Error occurred during unregister_on_hangup:')
trace.log_exception_quietly()
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