Lib/multiprocessing/synchronize.py

   1 #
   2 # Module implementing synchronization primitives
   3 #
   4 # multiprocessing/synchronize.py
   5 #
   6 # Copyright (c) 2006-2008, R Oudkerk --- see COPYING.txt
   7 #
   8
   9 __all__ = [
  10     'Lock', 'RLock', 'Semaphore', 'BoundedSemaphore', 'Condition', 'Event'
  11     ]
  12
  13 import threading
  14 import os
  15 import sys
  16
  17 from time import time as _time, sleep as _sleep
  18
  19 import _multiprocessing
  20 from multiprocessing.process import current_process
  21 from multiprocessing.util import Finalize, register_after_fork, debug
  22 from multiprocessing.forking import assert_spawning, Popen
  23
  24 # Try to import the mp.synchronize module cleanly, if it fails
  25 # raise ImportError for platforms lacking a working sem_open implementation.
  26 # See issue 3770
  27 try:
  28     from _multiprocessing import SemLock
  29 except (ImportError):
  30     raise ImportError("This platform lacks a functioning sem_open" +
  31                       " implementation, therefore, the required" +
  32                       " synchronization primitives needed will not" +
  33                       " function, see issue 3770.")
  34
  35 #
  36 # Constants
  37 #
  38
  39 RECURSIVE_MUTEX, SEMAPHORE = range(2)
  40 SEM_VALUE_MAX = _multiprocessing.SemLock.SEM_VALUE_MAX
  41
  42 #
  43 # Base class for semaphores and mutexes; wraps `_multiprocessing.SemLock`
  44 #
  45
  46 class SemLock(object):
  47
  48     def __init__(self, kind, value, maxvalue):
  49         sl = self._semlock = _multiprocessing.SemLock(kind, value, maxvalue)
  50         debug('created semlock with handle %s' % sl.handle)
  51         self._make_methods()
  52
  53         if sys.platform != 'win32':
  54             def _after_fork(obj):
  55                 obj._semlock._after_fork()
  56             register_after_fork(self, _after_fork)
  57
  58     def _make_methods(self):
  59         self.acquire = self._semlock.acquire
  60         self.release = self._semlock.release
  61
  62     def __enter__(self):
  63         return self._semlock.__enter__()
  64
  65     def __exit__(self, *args):
  66         return self._semlock.__exit__(*args)
  67
  68     def __getstate__(self):
  69         assert_spawning(self)
  70         sl = self._semlock
  71         return (Popen.duplicate_for_child(sl.handle), sl.kind, sl.maxvalue)
  72
  73     def __setstate__(self, state):
  74         self._semlock = _multiprocessing.SemLock._rebuild(*state)
  75         debug('recreated blocker with handle %r' % state[0])
  76         self._make_methods()
  77
  78 #
  79 # Semaphore
  80 #
  81
  82 class Semaphore(SemLock):
  83
  84     def __init__(self, value=1):
  85         SemLock.__init__(self, SEMAPHORE, value, SEM_VALUE_MAX)
  86
  87     def get_value(self):
  88         return self._semlock._get_value()
  89
  90     def __repr__(self):
  91         try:
  92             value = self._semlock._get_value()
  93         except Exception:
  94             value = 'unknown'
  95         return '<Semaphore(value=%s)>' % value
  96
  97 #
  98 # Bounded semaphore
  99 #
 100
 101 class BoundedSemaphore(Semaphore):
 102
 103     def __init__(self, value=1):
 104         SemLock.__init__(self, SEMAPHORE, value, value)
 105
 106     def __repr__(self):
 107         try:
 108             value = self._semlock._get_value()
 109         except Exception:
 110             value = 'unknown'
 111         return '<BoundedSemaphore(value=%s, maxvalue=%s)>' % \
 112                (value, self._semlock.maxvalue)
 113
 114 #
 115 # Non-recursive lock
 116 #
 117
 118 class Lock(SemLock):
 119
 120     def __init__(self):
 121         SemLock.__init__(self, SEMAPHORE, 1, 1)
 122
 123     def __repr__(self):
 124         try:
 125             if self._semlock._is_mine():
 126                 name = current_process().name
 127                 if threading.current_thread().name != 'MainThread':
 128                     name += '|' + threading.current_thread().name
 129             elif self._semlock._get_value() == 1:
 130                 name = 'None'
 131             elif self._semlock._count() > 0:
 132                 name = 'SomeOtherThread'
 133             else:
 134                 name = 'SomeOtherProcess'
 135         except Exception:
 136             name = 'unknown'
 137         return '<Lock(owner=%s)>' % name
 138
 139 #
 140 # Recursive lock
 141 #
 142
 143 class RLock(SemLock):
 144
 145     def __init__(self):
 146         SemLock.__init__(self, RECURSIVE_MUTEX, 1, 1)
 147
 148     def __repr__(self):
 149         try:
 150             if self._semlock._is_mine():
 151                 name = current_process().name
 152                 if threading.current_thread().name != 'MainThread':
 153                     name += '|' + threading.current_thread().name
 154                 count = self._semlock._count()
 155             elif self._semlock._get_value() == 1:
 156                 name, count = 'None', 0
 157             elif self._semlock._count() > 0:
 158                 name, count = 'SomeOtherThread', 'nonzero'
 159             else:
 160                 name, count = 'SomeOtherProcess', 'nonzero'
 161         except Exception:
 162             name, count = 'unknown', 'unknown'
 163         return '<RLock(%s, %s)>' % (name, count)
 164
 165 #
 166 # Condition variable
 167 #
 168
 169 class Condition(object):
 170
 171     def __init__(self, lock=None):
 172         self._lock = lock or RLock()
 173         self._sleeping_count = Semaphore(0)
 174         self._woken_count = Semaphore(0)
 175         self._wait_semaphore = Semaphore(0)
 176         self._make_methods()
 177
 178     def __getstate__(self):
 179         assert_spawning(self)
 180         return (self._lock, self._sleeping_count,
 181                 self._woken_count, self._wait_semaphore)
 182
 183     def __setstate__(self, state):
 184         (self._lock, self._sleeping_count,
 185          self._woken_count, self._wait_semaphore) = state
 186         self._make_methods()
 187
 188     def __enter__(self):
 189         return self._lock.__enter__()
 190
 191     def __exit__(self, *args):
 192         return self._lock.__exit__(*args)
 193
 194     def _make_methods(self):
 195         self.acquire = self._lock.acquire
 196         self.release = self._lock.release
 197
 198     def __repr__(self):
 199         try:
 200             num_waiters = (self._sleeping_count._semlock._get_value() -
 201                            self._woken_count._semlock._get_value())
 202         except Exception:
 203             num_waiters = 'unkown'
 204         return '<Condition(%s, %s)>' % (self._lock, num_waiters)
 205
 206     def wait(self, timeout=None):
 207         assert self._lock._semlock._is_mine(), \
 208                'must acquire() condition before using wait()'
 209
 210         # indicate that this thread is going to sleep
 211         self._sleeping_count.release()
 212
 213         # release lock
 214         count = self._lock._semlock._count()
 215         for i in xrange(count):
 216             self._lock.release()
 217
 218         try:
 219             # wait for notification or timeout
 220             self._wait_semaphore.acquire(True, timeout)
 221         finally:
 222             # indicate that this thread has woken
 223             self._woken_count.release()
 224
 225             # reacquire lock
 226             for i in xrange(count):
 227                 self._lock.acquire()
 228
 229     def notify(self):
 230         assert self._lock._semlock._is_mine(), 'lock is not owned'
 231         assert not self._wait_semaphore.acquire(False)
 232
 233         # to take account of timeouts since last notify() we subtract
 234         # woken_count from sleeping_count and rezero woken_count
 235         while self._woken_count.acquire(False):
 236             res = self._sleeping_count.acquire(False)
 237             assert res
 238
 239         if self._sleeping_count.acquire(False): # try grabbing a sleeper
 240             self._wait_semaphore.release()      # wake up one sleeper
 241             self._woken_count.acquire()         # wait for the sleeper to wake
 242
 243             # rezero _wait_semaphore in case a timeout just happened
 244             self._wait_semaphore.acquire(False)
 245
 246     def notify_all(self):
 247         assert self._lock._semlock._is_mine(), 'lock is not owned'
 248         assert not self._wait_semaphore.acquire(False)
 249
 250         # to take account of timeouts since last notify*() we subtract
 251         # woken_count from sleeping_count and rezero woken_count
 252         while self._woken_count.acquire(False):
 253             res = self._sleeping_count.acquire(False)
 254             assert res
 255
 256         sleepers = 0
 257         while self._sleeping_count.acquire(False):
 258             self._wait_semaphore.release()        # wake up one sleeper
 259             sleepers += 1
 260
 261         if sleepers:
 262             for i in xrange(sleepers):
 263                 self._woken_count.acquire()       # wait for a sleeper to wake
 264
 265             # rezero wait_semaphore in case some timeouts just happened
 266             while self._wait_semaphore.acquire(False):
 267                 pass
 268
 269 #
 270 # Event
 271 #
 272
 273 class Event(object):
 274
 275     def __init__(self):
 276         self._cond = Condition(Lock())
 277         self._flag = Semaphore(0)
 278
 279     def is_set(self):
 280         self._cond.acquire()
 281         try:
 282             if self._flag.acquire(False):
 283                 self._flag.release()
 284                 return True
 285             return False
 286         finally:
 287             self._cond.release()
 288
 289     def set(self):
 290         self._cond.acquire()
 291         try:
 292             self._flag.acquire(False)
 293             self._flag.release()
 294             self._cond.notify_all()
 295         finally:
 296             self._cond.release()
 297
 298     def clear(self):
 299         self._cond.acquire()
 300         try:
 301             self._flag.acquire(False)
 302         finally:
 303             self._cond.release()
 304
 305     def wait(self, timeout=None):
 306         self._cond.acquire()
 307         try:
 308             if self._flag.acquire(False):
 309                 self._flag.release()
 310             else:
 311                 self._cond.wait(timeout)
 312
 313             if self._flag.acquire(False):
 314                 self._flag.release()
 315                 return True
 316             return False
 317         finally:
 318             self._cond.release()