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Replace the 'spawn' start method with 'fork' start method for multiprocessing, on MacOS with python>=3.8 #27317

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Merged
gfwm2013 merged 2 commits into from
Sep 17, 2020
Merged

Replace the 'spawn' start method with 'fork' start method for multiprocessing, on MacOS with python>=3.8 #27317

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Replace the 'spawn' start method with 'fork' start method for multipr…
gfwm2013 Sep 15, 2020
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Replace the 'spawn' start method with 'fork' start method for multipr…
gfwm2013 Sep 15, 2020
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23 changes: 19 additions & 4 deletions python/paddle/reader/decorator.py
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Original file line number Diff line number Diff line change
Expand Up @@ -32,6 +32,21 @@
import zlib
import paddle.compat as cpt

# On macOS, the 'spawn' start method is now the default in Python3.8 multiprocessing,
# Paddle is currently unable to solve this, so forces the process to start using
# the 'fork' start method.
#
# TODO: This solution is not good, because the fork start method could lead to
# crashes of the subprocess. Figure out how to make 'spawn' work.
#
# For more details, please refer to
# https://docs.python.org/3/library/multiprocessing.html#contexts-and-start-methods
# https://bugs.python.org/issue33725
if sys.version_info >= (3, ):
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@zhhsplendid zhhsplendid Sep 15, 2020

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If this only fails for Python3.8, could we only use fork when the version_info refers to Python 3.8?

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@gfwm2013 gfwm2013 Sep 15, 2020

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Thanks, done.

fork_context = multiprocessing.get_context('fork')
else:
fork_context = multiprocessing


def cache(reader):
"""
Expand Down Expand Up @@ -560,9 +575,9 @@ def _read_into_queue(reader, queue):
six.reraise(*sys.exc_info())

def queue_reader():
queue = multiprocessing.Queue(queue_size)
queue = fork_context.Queue(queue_size)
for reader in readers:
p = multiprocessing.Process(
p = fork_context.Process(
target=_read_into_queue, args=(reader, queue))
p.start()

Expand Down Expand Up @@ -593,9 +608,9 @@ def _read_into_pipe(reader, conn):
def pipe_reader():
conns = []
for reader in readers:
parent_conn, child_conn = multiprocessing.Pipe()
parent_conn, child_conn = fork_context.Pipe()
conns.append(parent_conn)
p = multiprocessing.Process(
p = fork_context.Process(
target=_read_into_pipe, args=(reader, child_conn))
p.start()

Expand Down