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