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#-----------------------------------------------------------------------------
# Copyright (c) 2023, PyInstaller Development Team.
#
# Distributed under the terms of the GNU General Public License (version 2
# or later) with exception for distributing the bootloader.
#
# The full license is in the file COPYING.txt, distributed with this software.
#
# SPDX-License-Identifier: (GPL-2.0-or-later WITH Bootloader-exception)
#-----------------------------------------------------------------------------
# Test that we can start a nested `multiprocessing.Process` from within a `multiprocessing.Process`. See #7494.
import sys
import multiprocessing
def nested_process_function(queue):
print("Running nested sub-process!")
queue.put(2)
def process_function(queue):
print("Running sub-process!")
queue.put(1)
process = multiprocessing.Process(target=nested_process_function, args=(queue,))
process.start()
process.join()
def main(start_method):
multiprocessing.set_start_method(start_method)
queue = multiprocessing.Queue()
process = multiprocessing.Process(target=process_function, args=(queue,))
process.start()
process.join()
# Read results from queue; we expect one for each process.
# NOTE: this goes against the `multiprocessing` programming recommendations, because we should read from queue
# before joining the feeding processes, lest we incur a deadlock when queue's buffer fills up. However, as we put in
# only two elements, we take a calculated risk; this way, we can read only available items post-hoc, which in turn
# allows us to avoid blocking forever if a process happens to fail for some reason.
results = []
while not queue.empty():
results.append(queue.get())
# NOTE: as per [1]: "If multiple processes are enqueuing objects, it is possible for the objects to be received at
# the other end out-of-order. However, objects enqueued by the same process will always be in the expected order
# with respect to each other."
# [1] https://docs.python.org/3/library/multiprocessing.html#pipes-and-queues
#
# Therefore, accept either order of results as a valid one.
print(f"Results: {results}")
assert results == [1, 2] or results == [2, 1]
if __name__ == '__main__':
multiprocessing.freeze_support()
if len(sys.argv) != 2:
print(f"Usage: {sys.argv[0]} <start-method>")
sys.exit(1)
main(sys.argv[1])
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