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Date: Wed, 12 Sep 2012 11:20:02 +0100
Subject: forked processes and testing
From: andrea crotti <andrea.crotti.0@gmail.com>
To: python-list <python-list@python.org>
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Xref: csiph.com comp.lang.python:28941

I wrote a decorator that takes a function, run it in a forked process
and return the PID:

def on_forked_process(func):
    from os import fork
    """Decorator that forks the process, runs the function and gives
    back control to the main process
    """
    def _on_forked_process(*args, **kwargs):
        pid = fork()
        if pid == 0:
            func(*args, **kwargs)
            sys.exit(0)
        else:
            return pid

    return _on_forked_process

It seems in general to work but I'm not able to test it, for example this fails:

def test_on_forked_process(self):
    @utils.on_forked_process
    def _dummy_func():
        pass

    with self.assertRaises(SystemExit):
        retpid = _dummy_func()
        # pid of the son process should be always > 0
        self.assertTrue(retpid > 0)


and I'm not sure why, nose doesn't like the Exit apparently even if
it's happening in an unrelated proces..

Any idea of how to make it testable or improve it?

In theory probably I will not use it for production because I should
use something smarter to control the various processes I need to run,
but for my integration tests it's quite useful, because then I can
kill the processes like

    except KeyboardInterrupt:
        from os import kill
        from signal import SIGTERM
        print("Killing sink and worker")
        kill(sink_pid, SIGTERM)
        kill(worker_pid, SIGTERM)