~bzr-pqm/bzr/bzr.dev

# 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()