Guido van Rossum | 27b7c7e | 2013-10-17 13:40:50 -0700 | [diff] [blame] | 1 | """Synchronization primitives.""" |
| 2 | |
Guido van Rossum | a58d1c3 | 2013-11-24 22:32:09 -0800 | [diff] [blame] | 3 | __all__ = ['Lock', 'Event', 'Condition', 'Semaphore', 'BoundedSemaphore'] |
Guido van Rossum | 27b7c7e | 2013-10-17 13:40:50 -0700 | [diff] [blame] | 4 | |
| 5 | import collections |
| 6 | |
| 7 | from . import events |
| 8 | from . import futures |
| 9 | from . import tasks |
| 10 | |
| 11 | |
Guido van Rossum | ab3c889 | 2014-01-25 16:51:57 -0800 | [diff] [blame^] | 12 | class _ContextManager: |
| 13 | """Context manager. |
| 14 | |
| 15 | This enables the following idiom for acquiring and releasing a |
| 16 | lock around a block: |
| 17 | |
| 18 | with (yield from lock): |
| 19 | <block> |
| 20 | |
| 21 | while failing loudly when accidentally using: |
| 22 | |
| 23 | with lock: |
| 24 | <block> |
| 25 | """ |
| 26 | |
| 27 | def __init__(self, lock): |
| 28 | self._lock = lock |
| 29 | |
| 30 | def __enter__(self): |
| 31 | # We have no use for the "as ..." clause in the with |
| 32 | # statement for locks. |
| 33 | return None |
| 34 | |
| 35 | def __exit__(self, *args): |
| 36 | try: |
| 37 | self._lock.release() |
| 38 | finally: |
| 39 | self._lock = None # Crudely prevent reuse. |
| 40 | |
| 41 | |
Guido van Rossum | 27b7c7e | 2013-10-17 13:40:50 -0700 | [diff] [blame] | 42 | class Lock: |
| 43 | """Primitive lock objects. |
| 44 | |
| 45 | A primitive lock is a synchronization primitive that is not owned |
| 46 | by a particular coroutine when locked. A primitive lock is in one |
| 47 | of two states, 'locked' or 'unlocked'. |
| 48 | |
| 49 | It is created in the unlocked state. It has two basic methods, |
| 50 | acquire() and release(). When the state is unlocked, acquire() |
| 51 | changes the state to locked and returns immediately. When the |
| 52 | state is locked, acquire() blocks until a call to release() in |
| 53 | another coroutine changes it to unlocked, then the acquire() call |
| 54 | resets it to locked and returns. The release() method should only |
| 55 | be called in the locked state; it changes the state to unlocked |
| 56 | and returns immediately. If an attempt is made to release an |
| 57 | unlocked lock, a RuntimeError will be raised. |
| 58 | |
| 59 | When more than one coroutine is blocked in acquire() waiting for |
| 60 | the state to turn to unlocked, only one coroutine proceeds when a |
| 61 | release() call resets the state to unlocked; first coroutine which |
| 62 | is blocked in acquire() is being processed. |
| 63 | |
| 64 | acquire() is a coroutine and should be called with 'yield from'. |
| 65 | |
| 66 | Locks also support the context manager protocol. '(yield from lock)' |
| 67 | should be used as context manager expression. |
| 68 | |
| 69 | Usage: |
| 70 | |
| 71 | lock = Lock() |
| 72 | ... |
| 73 | yield from lock |
| 74 | try: |
| 75 | ... |
| 76 | finally: |
| 77 | lock.release() |
| 78 | |
| 79 | Context manager usage: |
| 80 | |
| 81 | lock = Lock() |
| 82 | ... |
| 83 | with (yield from lock): |
| 84 | ... |
| 85 | |
| 86 | Lock objects can be tested for locking state: |
| 87 | |
| 88 | if not lock.locked(): |
| 89 | yield from lock |
| 90 | else: |
| 91 | # lock is acquired |
| 92 | ... |
| 93 | |
| 94 | """ |
| 95 | |
| 96 | def __init__(self, *, loop=None): |
| 97 | self._waiters = collections.deque() |
| 98 | self._locked = False |
| 99 | if loop is not None: |
| 100 | self._loop = loop |
| 101 | else: |
| 102 | self._loop = events.get_event_loop() |
| 103 | |
| 104 | def __repr__(self): |
| 105 | res = super().__repr__() |
| 106 | extra = 'locked' if self._locked else 'unlocked' |
| 107 | if self._waiters: |
| 108 | extra = '{},waiters:{}'.format(extra, len(self._waiters)) |
| 109 | return '<{} [{}]>'.format(res[1:-1], extra) |
| 110 | |
| 111 | def locked(self): |
Victor Stinner | c37dd61 | 2013-12-02 14:31:16 +0100 | [diff] [blame] | 112 | """Return True if lock is acquired.""" |
Guido van Rossum | 27b7c7e | 2013-10-17 13:40:50 -0700 | [diff] [blame] | 113 | return self._locked |
| 114 | |
| 115 | @tasks.coroutine |
| 116 | def acquire(self): |
| 117 | """Acquire a lock. |
| 118 | |
| 119 | This method blocks until the lock is unlocked, then sets it to |
| 120 | locked and returns True. |
| 121 | """ |
| 122 | if not self._waiters and not self._locked: |
| 123 | self._locked = True |
| 124 | return True |
| 125 | |
| 126 | fut = futures.Future(loop=self._loop) |
| 127 | self._waiters.append(fut) |
| 128 | try: |
| 129 | yield from fut |
| 130 | self._locked = True |
| 131 | return True |
| 132 | finally: |
| 133 | self._waiters.remove(fut) |
| 134 | |
| 135 | def release(self): |
| 136 | """Release a lock. |
| 137 | |
| 138 | When the lock is locked, reset it to unlocked, and return. |
| 139 | If any other coroutines are blocked waiting for the lock to become |
| 140 | unlocked, allow exactly one of them to proceed. |
| 141 | |
| 142 | When invoked on an unlocked lock, a RuntimeError is raised. |
| 143 | |
| 144 | There is no return value. |
| 145 | """ |
| 146 | if self._locked: |
| 147 | self._locked = False |
| 148 | # Wake up the first waiter who isn't cancelled. |
| 149 | for fut in self._waiters: |
| 150 | if not fut.done(): |
| 151 | fut.set_result(True) |
| 152 | break |
| 153 | else: |
| 154 | raise RuntimeError('Lock is not acquired.') |
| 155 | |
| 156 | def __enter__(self): |
Guido van Rossum | ab3c889 | 2014-01-25 16:51:57 -0800 | [diff] [blame^] | 157 | raise RuntimeError( |
| 158 | '"yield from" should be used as context manager expression') |
Guido van Rossum | 27b7c7e | 2013-10-17 13:40:50 -0700 | [diff] [blame] | 159 | |
| 160 | def __exit__(self, *args): |
Guido van Rossum | ab3c889 | 2014-01-25 16:51:57 -0800 | [diff] [blame^] | 161 | # This must exist because __enter__ exists, even though that |
| 162 | # always raises; that's how the with-statement works. |
| 163 | pass |
Guido van Rossum | 27b7c7e | 2013-10-17 13:40:50 -0700 | [diff] [blame] | 164 | |
| 165 | def __iter__(self): |
Guido van Rossum | ab3c889 | 2014-01-25 16:51:57 -0800 | [diff] [blame^] | 166 | # This is not a coroutine. It is meant to enable the idiom: |
| 167 | # |
| 168 | # with (yield from lock): |
| 169 | # <block> |
| 170 | # |
| 171 | # as an alternative to: |
| 172 | # |
| 173 | # yield from lock.acquire() |
| 174 | # try: |
| 175 | # <block> |
| 176 | # finally: |
| 177 | # lock.release() |
Guido van Rossum | 27b7c7e | 2013-10-17 13:40:50 -0700 | [diff] [blame] | 178 | yield from self.acquire() |
Guido van Rossum | ab3c889 | 2014-01-25 16:51:57 -0800 | [diff] [blame^] | 179 | return _ContextManager(self) |
Guido van Rossum | 27b7c7e | 2013-10-17 13:40:50 -0700 | [diff] [blame] | 180 | |
| 181 | |
| 182 | class Event: |
Guido van Rossum | 994bf43 | 2013-12-19 12:47:38 -0800 | [diff] [blame] | 183 | """Asynchronous equivalent to threading.Event. |
Guido van Rossum | 27b7c7e | 2013-10-17 13:40:50 -0700 | [diff] [blame] | 184 | |
| 185 | Class implementing event objects. An event manages a flag that can be set |
| 186 | to true with the set() method and reset to false with the clear() method. |
| 187 | The wait() method blocks until the flag is true. The flag is initially |
| 188 | false. |
| 189 | """ |
| 190 | |
| 191 | def __init__(self, *, loop=None): |
| 192 | self._waiters = collections.deque() |
| 193 | self._value = False |
| 194 | if loop is not None: |
| 195 | self._loop = loop |
| 196 | else: |
| 197 | self._loop = events.get_event_loop() |
| 198 | |
| 199 | def __repr__(self): |
Guido van Rossum | 27b7c7e | 2013-10-17 13:40:50 -0700 | [diff] [blame] | 200 | res = super().__repr__() |
Guido van Rossum | ccea084 | 2013-11-04 13:18:19 -0800 | [diff] [blame] | 201 | extra = 'set' if self._value else 'unset' |
| 202 | if self._waiters: |
| 203 | extra = '{},waiters:{}'.format(extra, len(self._waiters)) |
| 204 | return '<{} [{}]>'.format(res[1:-1], extra) |
Guido van Rossum | 27b7c7e | 2013-10-17 13:40:50 -0700 | [diff] [blame] | 205 | |
| 206 | def is_set(self): |
Victor Stinner | c37dd61 | 2013-12-02 14:31:16 +0100 | [diff] [blame] | 207 | """Return True if and only if the internal flag is true.""" |
Guido van Rossum | 27b7c7e | 2013-10-17 13:40:50 -0700 | [diff] [blame] | 208 | return self._value |
| 209 | |
| 210 | def set(self): |
| 211 | """Set the internal flag to true. All coroutines waiting for it to |
| 212 | become true are awakened. Coroutine that call wait() once the flag is |
| 213 | true will not block at all. |
| 214 | """ |
| 215 | if not self._value: |
| 216 | self._value = True |
| 217 | |
| 218 | for fut in self._waiters: |
| 219 | if not fut.done(): |
| 220 | fut.set_result(True) |
| 221 | |
| 222 | def clear(self): |
| 223 | """Reset the internal flag to false. Subsequently, coroutines calling |
| 224 | wait() will block until set() is called to set the internal flag |
| 225 | to true again.""" |
| 226 | self._value = False |
| 227 | |
| 228 | @tasks.coroutine |
| 229 | def wait(self): |
| 230 | """Block until the internal flag is true. |
| 231 | |
| 232 | If the internal flag is true on entry, return True |
| 233 | immediately. Otherwise, block until another coroutine calls |
| 234 | set() to set the flag to true, then return True. |
| 235 | """ |
| 236 | if self._value: |
| 237 | return True |
| 238 | |
| 239 | fut = futures.Future(loop=self._loop) |
| 240 | self._waiters.append(fut) |
| 241 | try: |
| 242 | yield from fut |
| 243 | return True |
| 244 | finally: |
| 245 | self._waiters.remove(fut) |
| 246 | |
| 247 | |
Guido van Rossum | ccea084 | 2013-11-04 13:18:19 -0800 | [diff] [blame] | 248 | class Condition: |
Guido van Rossum | 994bf43 | 2013-12-19 12:47:38 -0800 | [diff] [blame] | 249 | """Asynchronous equivalent to threading.Condition. |
Guido van Rossum | 27b7c7e | 2013-10-17 13:40:50 -0700 | [diff] [blame] | 250 | |
| 251 | This class implements condition variable objects. A condition variable |
| 252 | allows one or more coroutines to wait until they are notified by another |
| 253 | coroutine. |
Guido van Rossum | ccea084 | 2013-11-04 13:18:19 -0800 | [diff] [blame] | 254 | |
| 255 | A new Lock object is created and used as the underlying lock. |
Guido van Rossum | 27b7c7e | 2013-10-17 13:40:50 -0700 | [diff] [blame] | 256 | """ |
| 257 | |
| 258 | def __init__(self, *, loop=None): |
Guido van Rossum | ccea084 | 2013-11-04 13:18:19 -0800 | [diff] [blame] | 259 | if loop is not None: |
| 260 | self._loop = loop |
| 261 | else: |
| 262 | self._loop = events.get_event_loop() |
Guido van Rossum | 27b7c7e | 2013-10-17 13:40:50 -0700 | [diff] [blame] | 263 | |
Guido van Rossum | ccea084 | 2013-11-04 13:18:19 -0800 | [diff] [blame] | 264 | # Lock as an attribute as in threading.Condition. |
| 265 | lock = Lock(loop=self._loop) |
| 266 | self._lock = lock |
| 267 | # Export the lock's locked(), acquire() and release() methods. |
| 268 | self.locked = lock.locked |
| 269 | self.acquire = lock.acquire |
| 270 | self.release = lock.release |
| 271 | |
| 272 | self._waiters = collections.deque() |
| 273 | |
| 274 | def __repr__(self): |
| 275 | res = super().__repr__() |
| 276 | extra = 'locked' if self.locked() else 'unlocked' |
| 277 | if self._waiters: |
| 278 | extra = '{},waiters:{}'.format(extra, len(self._waiters)) |
| 279 | return '<{} [{}]>'.format(res[1:-1], extra) |
Guido van Rossum | 27b7c7e | 2013-10-17 13:40:50 -0700 | [diff] [blame] | 280 | |
| 281 | @tasks.coroutine |
| 282 | def wait(self): |
| 283 | """Wait until notified. |
| 284 | |
| 285 | If the calling coroutine has not acquired the lock when this |
| 286 | method is called, a RuntimeError is raised. |
| 287 | |
| 288 | This method releases the underlying lock, and then blocks |
| 289 | until it is awakened by a notify() or notify_all() call for |
| 290 | the same condition variable in another coroutine. Once |
| 291 | awakened, it re-acquires the lock and returns True. |
| 292 | """ |
Guido van Rossum | ccea084 | 2013-11-04 13:18:19 -0800 | [diff] [blame] | 293 | if not self.locked(): |
Guido van Rossum | 27b7c7e | 2013-10-17 13:40:50 -0700 | [diff] [blame] | 294 | raise RuntimeError('cannot wait on un-acquired lock') |
| 295 | |
Guido van Rossum | 27b7c7e | 2013-10-17 13:40:50 -0700 | [diff] [blame] | 296 | self.release() |
| 297 | try: |
| 298 | fut = futures.Future(loop=self._loop) |
Guido van Rossum | ccea084 | 2013-11-04 13:18:19 -0800 | [diff] [blame] | 299 | self._waiters.append(fut) |
Guido van Rossum | 27b7c7e | 2013-10-17 13:40:50 -0700 | [diff] [blame] | 300 | try: |
| 301 | yield from fut |
| 302 | return True |
| 303 | finally: |
Guido van Rossum | ccea084 | 2013-11-04 13:18:19 -0800 | [diff] [blame] | 304 | self._waiters.remove(fut) |
Guido van Rossum | 27b7c7e | 2013-10-17 13:40:50 -0700 | [diff] [blame] | 305 | |
Guido van Rossum | 27b7c7e | 2013-10-17 13:40:50 -0700 | [diff] [blame] | 306 | finally: |
Guido van Rossum | 2407f3b | 2014-01-10 13:25:38 -0800 | [diff] [blame] | 307 | yield from self.acquire() |
Guido van Rossum | 27b7c7e | 2013-10-17 13:40:50 -0700 | [diff] [blame] | 308 | |
| 309 | @tasks.coroutine |
| 310 | def wait_for(self, predicate): |
| 311 | """Wait until a predicate becomes true. |
| 312 | |
| 313 | The predicate should be a callable which result will be |
| 314 | interpreted as a boolean value. The final predicate value is |
| 315 | the return value. |
| 316 | """ |
| 317 | result = predicate() |
| 318 | while not result: |
| 319 | yield from self.wait() |
| 320 | result = predicate() |
| 321 | return result |
| 322 | |
| 323 | def notify(self, n=1): |
| 324 | """By default, wake up one coroutine waiting on this condition, if any. |
| 325 | If the calling coroutine has not acquired the lock when this method |
| 326 | is called, a RuntimeError is raised. |
| 327 | |
| 328 | This method wakes up at most n of the coroutines waiting for the |
| 329 | condition variable; it is a no-op if no coroutines are waiting. |
| 330 | |
| 331 | Note: an awakened coroutine does not actually return from its |
| 332 | wait() call until it can reacquire the lock. Since notify() does |
| 333 | not release the lock, its caller should. |
| 334 | """ |
Guido van Rossum | ccea084 | 2013-11-04 13:18:19 -0800 | [diff] [blame] | 335 | if not self.locked(): |
Guido van Rossum | 27b7c7e | 2013-10-17 13:40:50 -0700 | [diff] [blame] | 336 | raise RuntimeError('cannot notify on un-acquired lock') |
| 337 | |
| 338 | idx = 0 |
Guido van Rossum | ccea084 | 2013-11-04 13:18:19 -0800 | [diff] [blame] | 339 | for fut in self._waiters: |
Guido van Rossum | 27b7c7e | 2013-10-17 13:40:50 -0700 | [diff] [blame] | 340 | if idx >= n: |
| 341 | break |
| 342 | |
| 343 | if not fut.done(): |
| 344 | idx += 1 |
| 345 | fut.set_result(False) |
| 346 | |
| 347 | def notify_all(self): |
| 348 | """Wake up all threads waiting on this condition. This method acts |
| 349 | like notify(), but wakes up all waiting threads instead of one. If the |
| 350 | calling thread has not acquired the lock when this method is called, |
| 351 | a RuntimeError is raised. |
| 352 | """ |
Guido van Rossum | ccea084 | 2013-11-04 13:18:19 -0800 | [diff] [blame] | 353 | self.notify(len(self._waiters)) |
| 354 | |
| 355 | def __enter__(self): |
Guido van Rossum | ab3c889 | 2014-01-25 16:51:57 -0800 | [diff] [blame^] | 356 | raise RuntimeError( |
| 357 | '"yield from" should be used as context manager expression') |
Guido van Rossum | ccea084 | 2013-11-04 13:18:19 -0800 | [diff] [blame] | 358 | |
| 359 | def __exit__(self, *args): |
Guido van Rossum | ab3c889 | 2014-01-25 16:51:57 -0800 | [diff] [blame^] | 360 | pass |
Guido van Rossum | ccea084 | 2013-11-04 13:18:19 -0800 | [diff] [blame] | 361 | |
| 362 | def __iter__(self): |
Guido van Rossum | ab3c889 | 2014-01-25 16:51:57 -0800 | [diff] [blame^] | 363 | # See comment in Lock.__iter__(). |
Guido van Rossum | ccea084 | 2013-11-04 13:18:19 -0800 | [diff] [blame] | 364 | yield from self.acquire() |
Guido van Rossum | ab3c889 | 2014-01-25 16:51:57 -0800 | [diff] [blame^] | 365 | return _ContextManager(self) |
Guido van Rossum | 27b7c7e | 2013-10-17 13:40:50 -0700 | [diff] [blame] | 366 | |
| 367 | |
| 368 | class Semaphore: |
| 369 | """A Semaphore implementation. |
| 370 | |
| 371 | A semaphore manages an internal counter which is decremented by each |
| 372 | acquire() call and incremented by each release() call. The counter |
| 373 | can never go below zero; when acquire() finds that it is zero, it blocks, |
| 374 | waiting until some other thread calls release(). |
| 375 | |
| 376 | Semaphores also support the context manager protocol. |
| 377 | |
Guido van Rossum | 085869b | 2013-11-23 15:09:16 -0800 | [diff] [blame] | 378 | The optional argument gives the initial value for the internal |
Guido van Rossum | 27b7c7e | 2013-10-17 13:40:50 -0700 | [diff] [blame] | 379 | counter; it defaults to 1. If the value given is less than 0, |
| 380 | ValueError is raised. |
Guido van Rossum | 27b7c7e | 2013-10-17 13:40:50 -0700 | [diff] [blame] | 381 | """ |
| 382 | |
Guido van Rossum | 085869b | 2013-11-23 15:09:16 -0800 | [diff] [blame] | 383 | def __init__(self, value=1, *, loop=None): |
Guido van Rossum | 27b7c7e | 2013-10-17 13:40:50 -0700 | [diff] [blame] | 384 | if value < 0: |
Guido van Rossum | 9c55a58 | 2013-11-21 11:07:45 -0800 | [diff] [blame] | 385 | raise ValueError("Semaphore initial value must be >= 0") |
Guido van Rossum | 27b7c7e | 2013-10-17 13:40:50 -0700 | [diff] [blame] | 386 | self._value = value |
Guido van Rossum | 27b7c7e | 2013-10-17 13:40:50 -0700 | [diff] [blame] | 387 | self._waiters = collections.deque() |
Guido van Rossum | 27b7c7e | 2013-10-17 13:40:50 -0700 | [diff] [blame] | 388 | if loop is not None: |
| 389 | self._loop = loop |
| 390 | else: |
| 391 | self._loop = events.get_event_loop() |
| 392 | |
| 393 | def __repr__(self): |
Guido van Rossum | 27b7c7e | 2013-10-17 13:40:50 -0700 | [diff] [blame] | 394 | res = super().__repr__() |
Guido van Rossum | ab3c889 | 2014-01-25 16:51:57 -0800 | [diff] [blame^] | 395 | extra = 'locked' if self.locked() else 'unlocked,value:{}'.format( |
Guido van Rossum | ccea084 | 2013-11-04 13:18:19 -0800 | [diff] [blame] | 396 | self._value) |
| 397 | if self._waiters: |
| 398 | extra = '{},waiters:{}'.format(extra, len(self._waiters)) |
| 399 | return '<{} [{}]>'.format(res[1:-1], extra) |
Guido van Rossum | 27b7c7e | 2013-10-17 13:40:50 -0700 | [diff] [blame] | 400 | |
| 401 | def locked(self): |
| 402 | """Returns True if semaphore can not be acquired immediately.""" |
Guido van Rossum | ab3c889 | 2014-01-25 16:51:57 -0800 | [diff] [blame^] | 403 | return self._value == 0 |
Guido van Rossum | 27b7c7e | 2013-10-17 13:40:50 -0700 | [diff] [blame] | 404 | |
| 405 | @tasks.coroutine |
| 406 | def acquire(self): |
| 407 | """Acquire a semaphore. |
| 408 | |
| 409 | If the internal counter is larger than zero on entry, |
| 410 | decrement it by one and return True immediately. If it is |
| 411 | zero on entry, block, waiting until some other coroutine has |
| 412 | called release() to make it larger than 0, and then return |
| 413 | True. |
| 414 | """ |
| 415 | if not self._waiters and self._value > 0: |
| 416 | self._value -= 1 |
Guido van Rossum | 27b7c7e | 2013-10-17 13:40:50 -0700 | [diff] [blame] | 417 | return True |
| 418 | |
| 419 | fut = futures.Future(loop=self._loop) |
| 420 | self._waiters.append(fut) |
| 421 | try: |
| 422 | yield from fut |
| 423 | self._value -= 1 |
Guido van Rossum | 27b7c7e | 2013-10-17 13:40:50 -0700 | [diff] [blame] | 424 | return True |
| 425 | finally: |
| 426 | self._waiters.remove(fut) |
| 427 | |
| 428 | def release(self): |
| 429 | """Release a semaphore, incrementing the internal counter by one. |
| 430 | When it was zero on entry and another coroutine is waiting for it to |
| 431 | become larger than zero again, wake up that coroutine. |
Guido van Rossum | 27b7c7e | 2013-10-17 13:40:50 -0700 | [diff] [blame] | 432 | """ |
Guido van Rossum | 27b7c7e | 2013-10-17 13:40:50 -0700 | [diff] [blame] | 433 | self._value += 1 |
Guido van Rossum | 27b7c7e | 2013-10-17 13:40:50 -0700 | [diff] [blame] | 434 | for waiter in self._waiters: |
| 435 | if not waiter.done(): |
| 436 | waiter.set_result(True) |
| 437 | break |
| 438 | |
| 439 | def __enter__(self): |
Guido van Rossum | ab3c889 | 2014-01-25 16:51:57 -0800 | [diff] [blame^] | 440 | raise RuntimeError( |
| 441 | '"yield from" should be used as context manager expression') |
Guido van Rossum | 27b7c7e | 2013-10-17 13:40:50 -0700 | [diff] [blame] | 442 | |
| 443 | def __exit__(self, *args): |
Guido van Rossum | ab3c889 | 2014-01-25 16:51:57 -0800 | [diff] [blame^] | 444 | pass |
Guido van Rossum | 27b7c7e | 2013-10-17 13:40:50 -0700 | [diff] [blame] | 445 | |
| 446 | def __iter__(self): |
Guido van Rossum | ab3c889 | 2014-01-25 16:51:57 -0800 | [diff] [blame^] | 447 | # See comment in Lock.__iter__(). |
Guido van Rossum | 27b7c7e | 2013-10-17 13:40:50 -0700 | [diff] [blame] | 448 | yield from self.acquire() |
Guido van Rossum | ab3c889 | 2014-01-25 16:51:57 -0800 | [diff] [blame^] | 449 | return _ContextManager(self) |
Guido van Rossum | 085869b | 2013-11-23 15:09:16 -0800 | [diff] [blame] | 450 | |
| 451 | |
| 452 | class BoundedSemaphore(Semaphore): |
| 453 | """A bounded semaphore implementation. |
| 454 | |
| 455 | This raises ValueError in release() if it would increase the value |
| 456 | above the initial value. |
| 457 | """ |
| 458 | |
| 459 | def __init__(self, value=1, *, loop=None): |
| 460 | self._bound_value = value |
| 461 | super().__init__(value, loop=loop) |
| 462 | |
| 463 | def release(self): |
| 464 | if self._value >= self._bound_value: |
| 465 | raise ValueError('BoundedSemaphore released too many times') |
| 466 | super().release() |