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Issue #14059: Implement multiprocessing.Barrier

This commit is contained in:
Richard Oudkerk 2012-06-15 18:26:07 +01:00
parent a6bc4b4c85
commit 3730a17a58
7 changed files with 426 additions and 12 deletions
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23
Doc/library/multiprocessing.rst
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@ -226,11 +226,11 @@ However, if you really do need to use some shared data then
holds Python objects and allows other processes to manipulate them using
proxies.
A manager returned by :func:`Manager` will support types :class:`list`,
:class:`dict`, :class:`Namespace`, :class:`Lock`, :class:`RLock`,
:class:`Semaphore`, :class:`BoundedSemaphore`, :class:`Condition`,
:class:`Event`, :class:`Queue`, :class:`Value` and :class:`Array`. For
example, ::
A manager returned by :func:`Manager` will support types
:class:`list`, :class:`dict`, :class:`Namespace`, :class:`Lock`,
:class:`RLock`, :class:`Semaphore`, :class:`BoundedSemaphore`,
:class:`Condition`, :class:`Event`, :class:`Barrier`,
:class:`Queue`, :class:`Value` and :class:`Array`. For example, ::
from multiprocessing import Process, Manager
@ -885,6 +885,12 @@ program as they are in a multithreaded program. See the documentation for
Note that one can also create synchronization primitives by using a manager
object -- see :ref:`multiprocessing-managers`.
.. class:: Barrier(parties[, action[, timeout]])
A barrier object: a clone of :class:`threading.Barrier`.
.. versionadded:: 3.3
.. class:: BoundedSemaphore([value])
A bounded semaphore object: a clone of :class:`threading.BoundedSemaphore`.
@ -1280,6 +1286,13 @@ their parent process exits. The manager classes are defined in the
It also supports creation of shared lists and dictionaries.
.. method:: Barrier(parties[, action[, timeout]])
Create a shared :class:`threading.Barrier` object and return a
proxy for it.
.. versionadded:: 3.3
.. method:: BoundedSemaphore([value])
Create a shared :class:`threading.BoundedSemaphore` object and return a

11
Lib/multiprocessing/__init__.py
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@ -23,8 +23,8 @@ __all__ = [
'Manager', 'Pipe', 'cpu_count', 'log_to_stderr', 'get_logger',
'allow_connection_pickling', 'BufferTooShort', 'TimeoutError',
'Lock', 'RLock', 'Semaphore', 'BoundedSemaphore', 'Condition',
'Event', 'Queue', 'SimpleQueue', 'JoinableQueue', 'Pool', 'Value', 'Array',
'RawValue', 'RawArray', 'SUBDEBUG', 'SUBWARNING',
'Event', 'Barrier', 'Queue', 'SimpleQueue', 'JoinableQueue', 'Pool',
'Value', 'Array', 'RawValue', 'RawArray', 'SUBDEBUG', 'SUBWARNING',
]
__author__ = 'R. Oudkerk (r.m.oudkerk@gmail.com)'
@ -186,6 +186,13 @@ def Event():
from multiprocessing.synchronize import Event
return Event()
def Barrier(parties, action=None, timeout=None):
'''
Returns a barrier object
'''
from multiprocessing.synchronize import Barrier
return Barrier(parties, action, timeout)
def Queue(maxsize=0):
'''
Returns a queue object

4
Lib/multiprocessing/dummy/__init__.py
View File

@ -35,7 +35,7 @@
__all__ = [
'Process', 'current_process', 'active_children', 'freeze_support',
'Lock', 'RLock', 'Semaphore', 'BoundedSemaphore', 'Condition',
'Event', 'Queue', 'Manager', 'Pipe', 'Pool', 'JoinableQueue'
'Event', 'Barrier', 'Queue', 'Manager', 'Pipe', 'Pool', 'JoinableQueue'
]
#
@ -49,7 +49,7 @@ import array
from multiprocessing.dummy.connection import Pipe
from threading import Lock, RLock, Semaphore, BoundedSemaphore
from threading import Event, Condition
from threading import Event, Condition, Barrier
from queue import Queue
#

21
Lib/multiprocessing/managers.py
View File

@ -993,6 +993,26 @@ class EventProxy(BaseProxy):
def wait(self, timeout=None):
return self._callmethod('wait', (timeout,))
class BarrierProxy(BaseProxy):
_exposed_ = ('__getattribute__', 'wait', 'abort', 'reset')
def wait(self, timeout=None):
return self._callmethod('wait', (timeout,))
def abort(self):
return self._callmethod('abort')
def reset(self):
return self._callmethod('reset')
@property
def parties(self):
return self._callmethod('__getattribute__', ('parties',))
@property
def n_waiting(self):
return self._callmethod('__getattribute__', ('n_waiting',))
@property
def broken(self):
return self._callmethod('__getattribute__', ('broken',))
class NamespaceProxy(BaseProxy):
_exposed_ = ('__getattribute__', '__setattr__', '__delattr__')
def __getattr__(self, key):
@ -1084,6 +1104,7 @@ SyncManager.register('Semaphore', threading.Semaphore, AcquirerProxy)
SyncManager.register('BoundedSemaphore', threading.BoundedSemaphore,
AcquirerProxy)
SyncManager.register('Condition', threading.Condition, ConditionProxy)
SyncManager.register('Barrier', threading.Barrier, BarrierProxy)
SyncManager.register('Pool', Pool, PoolProxy)
SyncManager.register('list', list, ListProxy)
SyncManager.register('dict', dict, DictProxy)

40
Lib/multiprocessing/synchronize.py
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@ -333,3 +333,43 @@ class Event(object):
return False
finally:
self._cond.release()
#
# Barrier
#
class Barrier(threading.Barrier):
def __init__(self, parties, action=None, timeout=None):
import struct
from multiprocessing.heap import BufferWrapper
wrapper = BufferWrapper(struct.calcsize('i') * 2)
cond = Condition()
self.__setstate__((parties, action, timeout, cond, wrapper))
self._state = 0
self._count = 0
def __setstate__(self, state):
(self._parties, self._action, self._timeout,
self._cond, self._wrapper) = state
self._array = self._wrapper.create_memoryview().cast('i')
def __getstate__(self):
return (self._parties, self._action, self._timeout,
self._cond, self._wrapper)
@property
def _state(self):
return self._array[0]
@_state.setter
def _state(self, value):
self._array[0] = value
@property
def _count(self):
return self._array[1]
@_count.setter
def _count(self, value):
self._array[1] = value

337
Lib/test/test_multiprocessing.py
View File

@ -18,6 +18,7 @@ import array
import socket
import random
import logging
import struct
import test.support
@ -1056,6 +1057,336 @@ class _TestEvent(BaseTestCase):
p.start()
self.assertEqual(wait(), True)
#
# Tests for Barrier - adapted from tests in test/lock_tests.py
#
# Many of the tests for threading.Barrier use a list as an atomic
# counter: a value is appended to increment the counter, and the
# length of the list gives the value. We use the class DummyList
# for the same purpose.
class _DummyList(object):
def __init__(self):
wrapper = multiprocessing.heap.BufferWrapper(struct.calcsize('i'))
lock = multiprocessing.Lock()
self.__setstate__((wrapper, lock))
self._lengthbuf[0] = 0
def __setstate__(self, state):
(self._wrapper, self._lock) = state
self._lengthbuf = self._wrapper.create_memoryview().cast('i')
def __getstate__(self):
return (self._wrapper, self._lock)
def append(self, _):
with self._lock:
self._lengthbuf[0] += 1
def __len__(self):
with self._lock:
return self._lengthbuf[0]
def _wait():
# A crude wait/yield function not relying on synchronization primitives.
time.sleep(0.01)
class Bunch(object):
"""
A bunch of threads.
"""
def __init__(self, namespace, f, args, n, wait_before_exit=False):
"""
Construct a bunch of `n` threads running the same function `f`.
If `wait_before_exit` is True, the threads won't terminate until
do_finish() is called.
"""
self.f = f
self.args = args
self.n = n
self.started = namespace.DummyList()
self.finished = namespace.DummyList()
self._can_exit = namespace.Value('i', not wait_before_exit)
for i in range(n):
namespace.Process(target=self.task).start()
def task(self):
pid = os.getpid()
self.started.append(pid)
try:
self.f(*self.args)
finally:
self.finished.append(pid)
while not self._can_exit.value:
_wait()
def wait_for_started(self):
while len(self.started) < self.n:
_wait()
def wait_for_finished(self):
while len(self.finished) < self.n:
_wait()
def do_finish(self):
self._can_exit.value = True
class AppendTrue(object):
def __init__(self, obj):
self.obj = obj
def __call__(self):
self.obj.append(True)
class _TestBarrier(BaseTestCase):
"""
Tests for Barrier objects.
"""
N = 5
defaultTimeout = 10.0 # XXX Slow Windows buildbots need generous timeout
def setUp(self):
self.barrier = self.Barrier(self.N, timeout=self.defaultTimeout)
def tearDown(self):
self.barrier.abort()
self.barrier = None
def DummyList(self):
if self.TYPE == 'threads':
return []
elif self.TYPE == 'manager':
return self.manager.list()
else:
return _DummyList()
def run_threads(self, f, args):
b = Bunch(self, f, args, self.N-1)
f(*args)
b.wait_for_finished()
@classmethod
def multipass(cls, barrier, results, n):
m = barrier.parties
assert m == cls.N
for i in range(n):
results[0].append(True)
assert len(results[1]) == i * m
barrier.wait()
results[1].append(True)
assert len(results[0]) == (i + 1) * m
barrier.wait()
try:
assert barrier.n_waiting == 0
except NotImplementedError:
pass
assert not barrier.broken
def test_barrier(self, passes=1):
"""
Test that a barrier is passed in lockstep
"""
results = [self.DummyList(), self.DummyList()]
self.run_threads(self.multipass, (self.barrier, results, passes))
def test_barrier_10(self):
"""
Test that a barrier works for 10 consecutive runs
"""
return self.test_barrier(10)
@classmethod
def _test_wait_return_f(cls, barrier, queue):
res = barrier.wait()
queue.put(res)
def test_wait_return(self):
"""
test the return value from barrier.wait
"""
queue = self.Queue()
self.run_threads(self._test_wait_return_f, (self.barrier, queue))
results = [queue.get() for i in range(self.N)]
self.assertEqual(results.count(0), 1)
@classmethod
def _test_action_f(cls, barrier, results):
barrier.wait()
if len(results) != 1:
raise RuntimeError
def test_action(self):
"""
Test the 'action' callback
"""
results = self.DummyList()
barrier = self.Barrier(self.N, action=AppendTrue(results))
self.run_threads(self._test_action_f, (barrier, results))
self.assertEqual(len(results), 1)
@classmethod
def _test_abort_f(cls, barrier, results1, results2):
try:
i = barrier.wait()
if i == cls.N//2:
raise RuntimeError
barrier.wait()
results1.append(True)
except threading.BrokenBarrierError:
results2.append(True)
except RuntimeError:
barrier.abort()
def test_abort(self):
"""
Test that an abort will put the barrier in a broken state
"""
results1 = self.DummyList()
results2 = self.DummyList()
self.run_threads(self._test_abort_f,
(self.barrier, results1, results2))
self.assertEqual(len(results1), 0)
self.assertEqual(len(results2), self.N-1)
self.assertTrue(self.barrier.broken)
@classmethod
def _test_reset_f(cls, barrier, results1, results2, results3):
i = barrier.wait()
if i == cls.N//2:
# Wait until the other threads are all in the barrier.
while barrier.n_waiting < cls.N-1:
time.sleep(0.001)
barrier.reset()
else:
try:
barrier.wait()
results1.append(True)
except threading.BrokenBarrierError:
results2.append(True)
# Now, pass the barrier again
barrier.wait()
results3.append(True)
def test_reset(self):
"""
Test that a 'reset' on a barrier frees the waiting threads
"""
results1 = self.DummyList()
results2 = self.DummyList()
results3 = self.DummyList()
self.run_threads(self._test_reset_f,
(self.barrier, results1, results2, results3))
self.assertEqual(len(results1), 0)
self.assertEqual(len(results2), self.N-1)
self.assertEqual(len(results3), self.N)
@classmethod
def _test_abort_and_reset_f(cls, barrier, barrier2,
results1, results2, results3):
try:
i = barrier.wait()
if i == cls.N//2:
raise RuntimeError
barrier.wait()
results1.append(True)
except threading.BrokenBarrierError:
results2.append(True)
except RuntimeError:
barrier.abort()
# Synchronize and reset the barrier. Must synchronize first so
# that everyone has left it when we reset, and after so that no
# one enters it before the reset.
if barrier2.wait() == cls.N//2:
barrier.reset()
barrier2.wait()
barrier.wait()
results3.append(True)
def test_abort_and_reset(self):
"""
Test that a barrier can be reset after being broken.
"""
results1 = self.DummyList()
results2 = self.DummyList()
results3 = self.DummyList()
barrier2 = self.Barrier(self.N)
self.run_threads(self._test_abort_and_reset_f,
(self.barrier, barrier2, results1, results2, results3))
self.assertEqual(len(results1), 0)
self.assertEqual(len(results2), self.N-1)
self.assertEqual(len(results3), self.N)
@classmethod
def _test_timeout_f(cls, barrier, results):
i = barrier.wait(20)
if i == cls.N//2:
# One thread is late!
time.sleep(4.0)
try:
barrier.wait(0.5)
except threading.BrokenBarrierError:
results.append(True)
def test_timeout(self):
"""
Test wait(timeout)
"""
results = self.DummyList()
self.run_threads(self._test_timeout_f, (self.barrier, results))
self.assertEqual(len(results), self.barrier.parties)
@classmethod
def _test_default_timeout_f(cls, barrier, results):
i = barrier.wait(20)
if i == cls.N//2:
# One thread is later than the default timeout
time.sleep(4.0)
try:
barrier.wait()
except threading.BrokenBarrierError:
results.append(True)
def test_default_timeout(self):
"""
Test the barrier's default timeout
"""
barrier = self.Barrier(self.N, timeout=1.0)
results = self.DummyList()
self.run_threads(self._test_default_timeout_f, (barrier, results))
self.assertEqual(len(results), barrier.parties)
def test_single_thread(self):
b = self.Barrier(1)
b.wait()
b.wait()
@classmethod
def _test_thousand_f(cls, barrier, passes, conn, lock):
for i in range(passes):
barrier.wait()
with lock:
conn.send(i)
def test_thousand(self):
if self.TYPE == 'manager':
return
passes = 1000
lock = self.Lock()
conn, child_conn = self.Pipe(False)
for j in range(self.N):
p = self.Process(target=self._test_thousand_f,
args=(self.barrier, passes, child_conn, lock))
p.start()
for i in range(passes):
for j in range(self.N):
self.assertEqual(conn.recv(), i)
#
#
#
@ -2532,7 +2863,7 @@ class ProcessesMixin(object):
Process = multiprocessing.Process
locals().update(get_attributes(multiprocessing, (
'Queue', 'Lock', 'RLock', 'Semaphore', 'BoundedSemaphore',
'Condition', 'Event', 'Value', 'Array', 'RawValue',
'Condition', 'Event', 'Barrier', 'Value', 'Array', 'RawValue',
'RawArray', 'current_process', 'active_children', 'Pipe',
'connection', 'JoinableQueue', 'Pool'
)))
@ -2547,7 +2878,7 @@ class ManagerMixin(object):
manager = object.__new__(multiprocessing.managers.SyncManager)
locals().update(get_attributes(manager, (
'Queue', 'Lock', 'RLock', 'Semaphore', 'BoundedSemaphore',
'Condition', 'Event', 'Value', 'Array', 'list', 'dict',
'Condition', 'Event', 'Barrier', 'Value', 'Array', 'list', 'dict',
'Namespace', 'JoinableQueue', 'Pool'
)))
@ -2560,7 +2891,7 @@ class ThreadsMixin(object):
Process = multiprocessing.dummy.Process
locals().update(get_attributes(multiprocessing.dummy, (
'Queue', 'Lock', 'RLock', 'Semaphore', 'BoundedSemaphore',
'Condition', 'Event', 'Value', 'Array', 'current_process',
'Condition', 'Event', 'Barrier', 'Value', 'Array', 'current_process',
'active_children', 'Pipe', 'connection', 'dict', 'list',
'Namespace', 'JoinableQueue', 'Pool'
)))

2
Misc/NEWS
View File

@ -21,6 +21,8 @@ Core and Builtins
Library
-------
- Issue #14059: Implement multiprocessing.Barrier.
- Issue #15061: The inappropriately named hmac.secure_compare has been
renamed to hmac.compare_digest, restricted to operating on bytes inputs
only and had its documentation updated to more accurately reflect both its