multiexit 1.4.0

=========
multiexit
=========

A better, saner and more useful atexit_ replacement for Python 3 that supports
multiprocessing_.

Inspired by the following StackOverflow question and experience on building
multiprocessing daemons:

https://stackoverflow.com/q/2546276

.. _atexit: https://docs.python.org/3/library/atexit.html
.. _multiprocessing: https://docs.python.org/3/library/multiprocessing.html

``multiexit`` will install a handler for the SIGTERM signal and execute the
registered exit functions in *LIFO* order (Last In First Out).

Exit functions can be registered so that only the calling process will call
them (the default), or as *shared* exit functions that will be called by the
calling process and all the children subprocesses that inherit it.


Install
=======

``multiexit`` is available for Python 3 from PyPI_.

.. _PyPI: https://pypi.python.org/pypi/multiexit/

.. code-block:: sh

pip3 install multiexit


API
===

On the main process, before forking or creating any subprocess,
call ``multiexit.install``:

.. code-block:: python

install(signals=(signal.SIGTERM, ), except_hook=True)

:signals:
Signals to install handler. Usually only ``SIGTERM`` is required.

:except_hook:
Also install a sys.excepthook_ that will call the exit functions in case of an
unexpected exception.

.. _excepthook: https://docs.python.org/3/library/sys.html#sys.excepthook

Then, for each exit function, on any subprocess, call ``multiexit.register``:

.. code-block:: python

register(func, shared=False)

:func:
Exit function to register. Any callable without arguments.

:shared:
If ``shared``, the exit function will be called by the calling process but
also by all the children subprocesses that inherit it (thus the ones
created after registering it).
If ``shared`` is ``False``, the default, only the calling process will execute
the exit function.


Example
=======

.. code-block:: python

from time import sleep
from signal import SIGTERM
from os import kill, getpid
from multiprocessing import Process

from multiexit import install, register, unregister


if __name__ == '__main__':

# Always call install() on the main process before creating any
# subprocess
#
# This will install a required handler for SIGTERM. Subprocesses must
# inherit this handler. Plus it assigns a pid as the master process
# for exit or os._exit call.
install()

def _subproc1():

@register
def subproc1_clean():
print('Subprocess clean!')

sleep(1000)

# Register shared exit function so all subprocess call this
def shared_exit():
print('Shared exit being called by {} ...'.format(getpid()))

register(shared_exit, shared=True)

subproc1 = Process(
name='SubProcess1',
target=_subproc1,
)
# proc.daemon = True
# daemon means that signals (like SIGTERM) will be propagated automatically
# to children. Set to false (the default), to handle the SIGTERM
# (process.terminate()) to the children yourself.
subproc1.start()

# Register a cleaner using a decorator
@register
def clean_main():
print('Terminating child {}'.format(
subproc1.pid,
))
subproc1.terminate()
subproc1.join()
print('Child {} ended with {}'.format(
subproc1.pid,
subproc1.exitcode,
))

# Wait, and then kill main process
sleep(3)

# Suicide
kill(getpid(), SIGTERM)

For a more extensive example check out ``example.py``.


License
=======

::

Copyright (C) 2018 KuraLabs S.R.L

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing,
software distributed under the License is distributed on an
"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
KIND, either express or implied. See the License for the
specific language governing permissions and limitations
under the License.