ganeti.workerpool

1 # 2 # 3 4 # Copyright (C) 2008, 2009, 2010 Google Inc. 5 # 6 # This program is free software; you can redistribute it and/or modify 7 # it under the terms of the GNU General Public License as published by 8 # the Free Software Foundation; either version 2 of the License, or 9 # (at your option) any later version. 10 # 11 # This program is distributed in the hope that it will be useful, but 12 # WITHOUT ANY WARRANTY; without even the implied warranty of 13 # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 14 # General Public License for more details. 15 # 16 # You should have received a copy of the GNU General Public License 17 # along with this program; if not, write to the Free Software 18 # Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 19 # 02110-1301, USA. 20 21 22 """Base classes for worker pools. 23 24 """ 25 26 import logging 27 import threading 28 import heapq 29 30 from ganeti import compat 31 from ganeti import errors 32 33 34 _TERMINATE = object() 35 _DEFAULT_PRIORITY = 0 36 37

38 -class DeferTask(Exception):

39 """Special exception class to defer a task. 40 41 This class can be raised by L{BaseWorker.RunTask} to defer the execution of a 42 task. Optionally, the priority of the task can be changed. 43 44 """

45 - def __init__(self, priority=None):

46 """Initializes this class. 47 48 @type priority: number 49 @param priority: New task priority (None means no change) 50 51 """ 52 Exception.__init__(self) 53 self.priority = priority

54 55

56 -class BaseWorker(threading.Thread, object):

57 """Base worker class for worker pools. 58 59 Users of a worker pool must override RunTask in a subclass. 60 61 """ 62 # pylint: disable-msg=W0212

63 - def __init__(self, pool, worker_id):

64 """Constructor for BaseWorker thread. 65 66 @param pool: the parent worker pool 67 @param worker_id: identifier for this worker 68 69 """ 70 super(BaseWorker, self).__init__(name=worker_id) 71 self.pool = pool 72 self._worker_id = worker_id 73 self._current_task = None 74 75 assert self.getName() == worker_id

76

77 - def ShouldTerminate(self):

78 """Returns whether this worker should terminate. 79 80 Should only be called from within L{RunTask}. 81 82 """ 83 self.pool._lock.acquire() 84 try: 85 assert self._HasRunningTaskUnlocked() 86 return self.pool._ShouldWorkerTerminateUnlocked(self) 87 finally: 88 self.pool._lock.release()

89

90 - def GetCurrentPriority(self):

91 """Returns the priority of the current task. 92 93 Should only be called from within L{RunTask}. 94 95 """ 96 self.pool._lock.acquire() 97 try: 98 assert self._HasRunningTaskUnlocked() 99 100 (priority, _, _) = self._current_task 101 102 return priority 103 finally: 104 self.pool._lock.release()

105

106 - def SetTaskName(self, taskname):

107 """Sets the name of the current task. 108 109 Should only be called from within L{RunTask}. 110 111 @type taskname: string 112 @param taskname: Task's name 113 114 """ 115 if taskname: 116 name = "%s/%s" % (self._worker_id, taskname) 117 else: 118 name = self._worker_id 119 120 # Set thread name 121 self.setName(name)

122

123 - def _HasRunningTaskUnlocked(self):

124 """Returns whether this worker is currently running a task. 125 126 """ 127 return (self._current_task is not None)

128

129 - def run(self):

130 """Main thread function. 131 132 Waits for new tasks to show up in the queue. 133 134 """ 135 pool = self.pool 136 137 while True: 138 assert self._current_task is None 139 140 defer = None 141 try: 142 # Wait on lock to be told either to terminate or to do a task 143 pool._lock.acquire() 144 try: 145 task = pool._WaitForTaskUnlocked(self) 146 147 if task is _TERMINATE: 148 # Told to terminate 149 break 150 151 if task is None: 152 # Spurious notification, ignore 153 continue 154 155 self._current_task = task 156 157 # No longer needed, dispose of reference 158 del task 159 160 assert self._HasRunningTaskUnlocked() 161 162 finally: 163 pool._lock.release() 164 165 (priority, _, args) = self._current_task 166 try: 167 # Run the actual task 168 assert defer is None 169 logging.debug("Starting task %r, priority %s", args, priority) 170 assert self.getName() == self._worker_id 171 try: 172 self.RunTask(*args) # pylint: disable-msg=W0142 173 finally: 174 self.SetTaskName(None) 175 logging.debug("Done with task %r, priority %s", args, priority) 176 except DeferTask, err: 177 defer = err 178 179 if defer.priority is None: 180 # Use same priority 181 defer.priority = priority 182 183 logging.debug("Deferring task %r, new priority %s", 184 args, defer.priority) 185 186 assert self._HasRunningTaskUnlocked() 187 except: # pylint: disable-msg=W0702 188 logging.exception("Caught unhandled exception") 189 190 assert self._HasRunningTaskUnlocked() 191 finally: 192 # Notify pool 193 pool._lock.acquire() 194 try: 195 if defer: 196 assert self._current_task 197 # Schedule again for later run 198 (_, _, args) = self._current_task 199 pool._AddTaskUnlocked(args, defer.priority) 200 201 if self._current_task: 202 self._current_task = None 203 pool._worker_to_pool.notifyAll() 204 finally: 205 pool._lock.release() 206 207 assert not self._HasRunningTaskUnlocked() 208 209 logging.debug("Terminates")

210

211 - def RunTask(self, *args):

212 """Function called to start a task. 213 214 This needs to be implemented by child classes. 215 216 """ 217 raise NotImplementedError()

218 219

220 -class WorkerPool(object):

221 """Worker pool with a queue. 222 223 This class is thread-safe. 224 225 Tasks are guaranteed to be started in the order in which they're 226 added to the pool. Due to the nature of threading, they're not 227 guaranteed to finish in the same order. 228 229 """

230 - def __init__(self, name, num_workers, worker_class):

231 """Constructor for worker pool. 232 233 @param num_workers: number of workers to be started 234 (dynamic resizing is not yet implemented) 235 @param worker_class: the class to be instantiated for workers; 236 should derive from L{BaseWorker} 237 238 """ 239 # Some of these variables are accessed by BaseWorker 240 self._lock = threading.Lock() 241 self._pool_to_pool = threading.Condition(self._lock) 242 self._pool_to_worker = threading.Condition(self._lock) 243 self._worker_to_pool = threading.Condition(self._lock) 244 self._worker_class = worker_class 245 self._name = name 246 self._last_worker_id = 0 247 self._workers = [] 248 self._quiescing = False 249 250 # Terminating workers 251 self._termworkers = [] 252 253 # Queued tasks 254 self._counter = 0 255 self._tasks = [] 256 257 # Start workers 258 self.Resize(num_workers)

259 260 # TODO: Implement dynamic resizing? 261

262 - def _WaitWhileQuiescingUnlocked(self):

263 """Wait until the worker pool has finished quiescing. 264 265 """ 266 while self._quiescing: 267 self._pool_to_pool.wait()

268

269 - def _AddTaskUnlocked(self, args, priority):

270 """Adds a task to the internal queue. 271 272 @type args: sequence 273 @param args: Arguments passed to L{BaseWorker.RunTask} 274 @type priority: number 275 @param priority: Task priority 276 277 """ 278 assert isinstance(args, (tuple, list)), "Arguments must be a sequence" 279 assert isinstance(priority, (int, long)), "Priority must be numeric" 280 281 # This counter is used to ensure elements are processed in their 282 # incoming order. For processing they're sorted by priority and then 283 # counter. 284 self._counter += 1 285 286 heapq.heappush(self._tasks, (priority, self._counter, args)) 287 288 # Notify a waiting worker 289 self._pool_to_worker.notify()

290

291 - def AddTask(self, args, priority=_DEFAULT_PRIORITY):

292 """Adds a task to the queue. 293 294 @type args: sequence 295 @param args: arguments passed to L{BaseWorker.RunTask} 296 @type priority: number 297 @param priority: Task priority 298 299 """ 300 self._lock.acquire() 301 try: 302 self._WaitWhileQuiescingUnlocked() 303 self._AddTaskUnlocked(args, priority) 304 finally: 305 self._lock.release()

306

307 - def AddManyTasks(self, tasks, priority=_DEFAULT_PRIORITY):

308 """Add a list of tasks to the queue. 309 310 @type tasks: list of tuples 311 @param tasks: list of args passed to L{BaseWorker.RunTask} 312 @type priority: number or list of numbers 313 @param priority: Priority for all added tasks or a list with the priority 314 for each task 315 316 """ 317 assert compat.all(isinstance(task, (tuple, list)) for task in tasks), \ 318 "Each task must be a sequence" 319 320 assert (isinstance(priority, (int, long)) or 321 compat.all(isinstance(prio, (int, long)) for prio in priority)), \ 322 "Priority must be numeric or be a list of numeric values" 323 324 if isinstance(priority, (int, long)): 325 priority = [priority] * len(tasks) 326 elif len(priority) != len(tasks): 327 raise errors.ProgrammerError("Number of priorities (%s) doesn't match" 328 " number of tasks (%s)" % 329 (len(priority), len(tasks))) 330 331 self._lock.acquire() 332 try: 333 self._WaitWhileQuiescingUnlocked() 334 335 assert compat.all(isinstance(prio, (int, long)) for prio in priority) 336 assert len(tasks) == len(priority) 337 338 for args, priority in zip(tasks, priority): 339 self._AddTaskUnlocked(args, priority) 340 finally: 341 self._lock.release()

342

343 - def _WaitForTaskUnlocked(self, worker):

344 """Waits for a task for a worker. 345 346 @type worker: L{BaseWorker} 347 @param worker: Worker thread 348 349 """ 350 if self._ShouldWorkerTerminateUnlocked(worker): 351 return _TERMINATE 352 353 # We only wait if there's no task for us. 354 if not self._tasks: 355 logging.debug("Waiting for tasks") 356 357 # wait() releases the lock and sleeps until notified 358 self._pool_to_worker.wait() 359 360 logging.debug("Notified while waiting") 361 362 # Were we woken up in order to terminate? 363 if self._ShouldWorkerTerminateUnlocked(worker): 364 return _TERMINATE 365 366 if not self._tasks: 367 # Spurious notification, ignore 368 return None 369 370 # Get task from queue and tell pool about it 371 try: 372 return heapq.heappop(self._tasks) 373 finally: 374 self._worker_to_pool.notifyAll()

375

376 - def _ShouldWorkerTerminateUnlocked(self, worker):

377 """Returns whether a worker should terminate. 378 379 """ 380 return (worker in self._termworkers)

381

382 - def _HasRunningTasksUnlocked(self):

383 """Checks whether there's a task running in a worker. 384 385 """ 386 for worker in self._workers + self._termworkers: 387 if worker._HasRunningTaskUnlocked(): # pylint: disable-msg=W0212 388 return True 389 return False

390

391 - def Quiesce(self):

392 """Waits until the task queue is empty. 393 394 """ 395 self._lock.acquire() 396 try: 397 self._quiescing = True 398 399 # Wait while there are tasks pending or running 400 while self._tasks or self._HasRunningTasksUnlocked(): 401 self._worker_to_pool.wait() 402 403 finally: 404 self._quiescing = False 405 406 # Make sure AddTasks continues in case it was waiting 407 self._pool_to_pool.notifyAll() 408 409 self._lock.release()

410

411 - def _NewWorkerIdUnlocked(self):

412 """Return an identifier for a new worker. 413 414 """ 415 self._last_worker_id += 1 416 417 return "%s%d" % (self._name, self._last_worker_id)

418

419 - def _ResizeUnlocked(self, num_workers):

420 """Changes the number of workers. 421 422 """ 423 assert num_workers >= 0, "num_workers must be >= 0" 424 425 logging.debug("Resizing to %s workers", num_workers) 426 427 current_count = len(self._workers) 428 429 if current_count == num_workers: 430 # Nothing to do 431 pass 432 433 elif current_count > num_workers: 434 if num_workers == 0: 435 # Create copy of list to iterate over while lock isn't held. 436 termworkers = self._workers[:] 437 del self._workers[:] 438 else: 439 # TODO: Implement partial downsizing 440 raise NotImplementedError() 441 #termworkers = ... 442 443 self._termworkers += termworkers 444 445 # Notify workers that something has changed 446 self._pool_to_worker.notifyAll() 447 448 # Join all terminating workers 449 self._lock.release() 450 try: 451 for worker in termworkers: 452 logging.debug("Waiting for thread %s", worker.getName()) 453 worker.join() 454 finally: 455 self._lock.acquire() 456 457 # Remove terminated threads. This could be done in a more efficient way 458 # (del self._termworkers[:]), but checking worker.isAlive() makes sure we 459 # don't leave zombie threads around. 460 for worker in termworkers: 461 assert worker in self._termworkers, ("Worker not in list of" 462 " terminating workers") 463 if not worker.isAlive(): 464 self._termworkers.remove(worker) 465 466 assert not self._termworkers, "Zombie worker detected" 467 468 elif current_count < num_workers: 469 # Create (num_workers - current_count) new workers 470 for _ in range(num_workers - current_count): 471 worker = self._worker_class(self, self._NewWorkerIdUnlocked()) 472 self._workers.append(worker) 473 worker.start()

474

475 - def Resize(self, num_workers):

476 """Changes the number of workers in the pool. 477 478 @param num_workers: the new number of workers 479 480 """ 481 self._lock.acquire() 482 try: 483 return self._ResizeUnlocked(num_workers) 484 finally: 485 self._lock.release()

486

487 - def TerminateWorkers(self):

488 """Terminate all worker threads. 489 490 Unstarted tasks will be ignored. 491 492 """ 493 logging.debug("Terminating all workers") 494 495 self._lock.acquire() 496 try: 497 self._ResizeUnlocked(0) 498 499 if self._tasks: 500 logging.debug("There are %s tasks left", len(self._tasks)) 501 finally: 502 self._lock.release() 503 504 logging.debug("All workers terminated")

505

Source Code for Module ganeti.workerpool