================================================================
:mod:`PyObjCTools.MachSignals` -- signal handling in a CFRunLoop
================================================================

.. module:: PyObjCTools.MachSignals
   :synopsis: signal handling in a CFRunLoop

Substitute for the signal module when using a CFRunLoop.

This module is generally only used to support::

    PyObjCTools.AppHelper.installMachInterrupt()

A mach port is opened and registered to the CFRunLoop.
When a signal occurs the signal number is sent in a mach
message to the CFRunLoop.  The handler then causes Python
code to get executed.

In other words, Python's signal handling code does not wake
reliably when not running Python code, but this does.

.. function:: getsignal(signum)
   Return the signal handler for signal ``signum``. Returns ``None`` when
   there is no signal handler for the signal.

.. function:: signal(signum, handler)
   Install a new signal handler for *signum*.

   Returns the old signal handler, or :data:`None` when there is
   no previous handler.
