Calling pselect/ppoll/epoll_pwait

[Ian Pilcher]

On 12/2/22 14:00, Ian Pilcher wrote:
> Does Python provide any way to call the "p" variants of the I/O
> multiplexing functions?

Just to close this out ...

As others suggested, there's no easy way to call the "p" variants of the
I/O multiplexing functions, but this can be worked around by "mapping"
signals to file descriptors.

There are a few ways to accomplish this.

1. Use a Linux signalfd.  There's at least one library out there that
    provides signalfd support to Python.

2. Use signal.set_wakeup_fd()[1].  I didn't really explore this, as it
    appears that there isn't any way to filter the signals that will be
    reported.

3. Roll your own.  This turned out to be really simple for my use case,
    which is simply to set an exit flag and wake my program up if it
    receives SIGINT or SIGTERM.

    _sel = selectors.DefaultSelector()
    _exit_flag = False
    _sig_pipe_r, _sig_pipe_w = os.pipe2(os.O_NONBLOCK | os.O_CLOEXEC)

    def _sig_handler(signum, frame):
        global _exit_flag
        _exit_flag = True
        os.write(_sig_pipe_w, b'\x00')

    _sel.register(_sig_pipe_r, selectors.EVENT_READ)
    # register other file descriptors of interest
    signal.signal(signal.SIGINT, _sig_handler)
    signal.signal(signal.SIGTERM, _sig_handler)
    while not _exit_flag:
        ready = _sel.select()
        # handle other file descriptors

[1] https://docs.python.org/3/library/signal.html#signal.set_wakeup_fd

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