Class _PidfdChildWatcher

Lib/asyncio/unix_events.py:857–891

Child watcher implementation using Linux's pid file descriptors. This child watcher polls process file descriptors (pidfds) to await child process termination. In some respects, PidfdChildWatcher is a "Goldilocks" child watcher implementation. It doesn't require signals or threads, does

class _PidfdChildWatcher:
    """Child watcher implementation using Linux's pid file descriptors.

    This child watcher polls process file descriptors (pidfds) to await child
    process termination. In some respects, PidfdChildWatcher is a "Goldilocks"
    child watcher implementation. It doesn't require signals or threads, doesn't
    interfere with any processes launched outside the event loop, and scales
    linearly with the number of subprocesses launched by the event loop. The
    main disadvantage is that pidfds are specific to Linux, and only work on
    recent (5.3+) kernels.
    """

    def add_child_handler(self, pid, callback, *args):
        loop = events.get_running_loop()
        pidfd = os.pidfd_open(pid)
        loop._add_reader(pidfd, self._do_wait, pid, pidfd, callback, args)

    def _do_wait(self, pid, pidfd, callback, args):
        loop = events.get_running_loop()
        loop._remove_reader(pidfd)
        try:
            _, status = os.waitpid(pid, 0)
        except ChildProcessError:
            # The child process is already reaped
            # (may happen if waitpid() is called elsewhere).
            returncode = 255
            logger.warning(
                "child process pid %d exit status already read: "
                " will report returncode 255",
                pid)
        else:
            returncode = waitstatus_to_exitcode(status)

        os.close(pidfd)
        callback(pid, returncode, *args)

class _ThreadedChildWatcher:
    """Threaded child watcher implementation.