root / lib / workerpool.py @ ed008420
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# Copyright (C) 2008 Google Inc.
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#
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# This program is free software; you can redistribute it and/or modify
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# it under the terms of the GNU General Public License as published by
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# the Free Software Foundation; either version 2 of the License, or
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# (at your option) any later version.
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#
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# This program is distributed in the hope that it will be useful, but
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# WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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# General Public License for more details.
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#
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# You should have received a copy of the GNU General Public License
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# along with this program; if not, write to the Free Software
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# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
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# 02110-1301, USA.
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"""Base classes for worker pools.
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"""
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import collections |
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import logging |
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import threading |
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class BaseWorker(threading.Thread, object): |
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"""Base worker class for worker pools.
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Users of a worker pool must override RunTask in a subclass.
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"""
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def __init__(self, pool, worker_id): |
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"""Constructor for BaseWorker thread.
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@param pool: the parent worker pool
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@param worker_id: identifier for this worker
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"""
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super(BaseWorker, self).__init__() |
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self.pool = pool
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self.worker_id = worker_id
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self._current_task = None |
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def ShouldTerminate(self): |
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"""Returns whether a worker should terminate.
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"""
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return self.pool.ShouldWorkerTerminate(self) |
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def _HasRunningTaskUnlocked(self): |
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"""Returns whether this worker is currently running a task.
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"""
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return (self._current_task is not None) |
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def HasRunningTask(self): |
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"""Returns whether this worker is currently running a task.
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"""
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self.pool._lock.acquire()
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try:
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return self._HasRunningTaskUnlocked() |
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finally:
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self.pool._lock.release()
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def run(self): |
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"""Main thread function.
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Waits for new tasks to show up in the queue.
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"""
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pool = self.pool
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assert not self.HasRunningTask() |
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while True: |
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try:
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# We wait on lock to be told either terminate or do a task.
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pool._lock.acquire() |
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try:
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if pool._ShouldWorkerTerminateUnlocked(self): |
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break
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# We only wait if there's no task for us.
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if not pool._tasks: |
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logging.debug("Worker %s: waiting for tasks", self.worker_id) |
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# wait() releases the lock and sleeps until notified
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pool._pool_to_worker.wait() |
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logging.debug("Worker %s: notified while waiting", self.worker_id) |
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# Were we woken up in order to terminate?
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if pool._ShouldWorkerTerminateUnlocked(self): |
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break
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if not pool._tasks: |
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# Spurious notification, ignore
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continue
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# Get task from queue and tell pool about it
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try:
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self._current_task = pool._tasks.popleft()
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finally:
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pool._worker_to_pool.notifyAll() |
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finally:
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pool._lock.release() |
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# Run the actual task
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try:
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logging.debug("Worker %s: starting task %r",
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self.worker_id, self._current_task) |
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self.RunTask(*self._current_task) |
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logging.debug("Worker %s: done with task %r",
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self.worker_id, self._current_task) |
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except:
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logging.error("Worker %s: Caught unhandled exception",
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self.worker_id, exc_info=True) |
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finally:
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# Notify pool
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pool._lock.acquire() |
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try:
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if self._current_task: |
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self._current_task = None |
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pool._worker_to_pool.notifyAll() |
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finally:
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pool._lock.release() |
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logging.debug("Worker %s: terminates", self.worker_id) |
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def RunTask(self, *args): |
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"""Function called to start a task.
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This needs to be implemented by child classes.
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"""
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raise NotImplementedError() |
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class WorkerPool(object): |
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"""Worker pool with a queue.
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This class is thread-safe.
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Tasks are guaranteed to be started in the order in which they're
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added to the pool. Due to the nature of threading, they're not
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guaranteed to finish in the same order.
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"""
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def __init__(self, num_workers, worker_class): |
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"""Constructor for worker pool.
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@param num_workers: number of workers to be started
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(dynamic resizing is not yet implemented)
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@param worker_class: the class to be instantiated for workers;
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should derive from L{BaseWorker}
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"""
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# Some of these variables are accessed by BaseWorker
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self._lock = threading.Lock()
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self._pool_to_pool = threading.Condition(self._lock) |
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self._pool_to_worker = threading.Condition(self._lock) |
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self._worker_to_pool = threading.Condition(self._lock) |
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self._worker_class = worker_class
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self._last_worker_id = 0 |
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self._workers = []
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self._quiescing = False |
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# Terminating workers
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self._termworkers = []
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# Queued tasks
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self._tasks = collections.deque()
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# Start workers
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self.Resize(num_workers)
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# TODO: Implement dynamic resizing?
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def AddTask(self, *args): |
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"""Adds a task to the queue.
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@param args: arguments passed to L{BaseWorker.RunTask}
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"""
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self._lock.acquire()
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try:
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# Don't add new tasks while we're quiescing
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while self._quiescing: |
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self._pool_to_pool.wait()
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# Add task to internal queue
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self._tasks.append(args)
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# Wake one idling worker up
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self._pool_to_worker.notify()
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finally:
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self._lock.release()
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def _ShouldWorkerTerminateUnlocked(self, worker): |
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"""Returns whether a worker should terminate.
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"""
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return (worker in self._termworkers) |
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def ShouldWorkerTerminate(self, worker): |
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"""Returns whether a worker should terminate.
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"""
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self._lock.acquire()
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try:
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return self._ShouldWorkerTerminateUnlocked(worker) |
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finally:
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self._lock.release()
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def _HasRunningTasksUnlocked(self): |
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"""Checks whether there's a task running in a worker.
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"""
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for worker in self._workers + self._termworkers: |
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if worker._HasRunningTaskUnlocked():
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return True |
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return False |
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def Quiesce(self): |
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"""Waits until the task queue is empty.
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"""
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self._lock.acquire()
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try:
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self._quiescing = True |
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# Wait while there are tasks pending or running
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while self._tasks or self._HasRunningTasksUnlocked(): |
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self._worker_to_pool.wait()
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finally:
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self._quiescing = False |
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# Make sure AddTasks continues in case it was waiting
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self._pool_to_pool.notifyAll()
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self._lock.release()
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def _NewWorkerIdUnlocked(self): |
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"""Return an identifier for a new worker.
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"""
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self._last_worker_id += 1 |
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return self._last_worker_id |
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def _ResizeUnlocked(self, num_workers): |
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"""Changes the number of workers.
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"""
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assert num_workers >= 0, "num_workers must be >= 0" |
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logging.debug("Resizing to %s workers", num_workers)
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current_count = len(self._workers) |
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if current_count == num_workers:
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# Nothing to do
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pass
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elif current_count > num_workers:
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if num_workers == 0: |
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# Create copy of list to iterate over while lock isn't held.
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termworkers = self._workers[:]
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del self._workers[:] |
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else:
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# TODO: Implement partial downsizing
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raise NotImplementedError() |
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#termworkers = ...
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self._termworkers += termworkers
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# Notify workers that something has changed
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self._pool_to_worker.notifyAll()
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# Join all terminating workers
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self._lock.release()
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try:
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for worker in termworkers: |
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logging.debug("Waiting for thread %s", worker.getName())
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worker.join() |
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finally:
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self._lock.acquire()
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# Remove terminated threads. This could be done in a more efficient way
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# (del self._termworkers[:]), but checking worker.isAlive() makes sure we
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# don't leave zombie threads around.
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for worker in termworkers: |
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assert worker in self._termworkers, ("Worker not in list of" |
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" terminating workers")
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if not worker.isAlive(): |
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self._termworkers.remove(worker)
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assert not self._termworkers, "Zombie worker detected" |
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elif current_count < num_workers:
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# Create (num_workers - current_count) new workers
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for _ in xrange(num_workers - current_count): |
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worker = self._worker_class(self, self._NewWorkerIdUnlocked()) |
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self._workers.append(worker)
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worker.start() |
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def Resize(self, num_workers): |
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"""Changes the number of workers in the pool.
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@param num_workers: the new number of workers
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"""
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self._lock.acquire()
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try:
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return self._ResizeUnlocked(num_workers) |
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finally:
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self._lock.release()
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def TerminateWorkers(self): |
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"""Terminate all worker threads.
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Unstarted tasks will be ignored.
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"""
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logging.debug("Terminating all workers")
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self._lock.acquire()
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try:
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self._ResizeUnlocked(0) |
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if self._tasks: |
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logging.debug("There are %s tasks left", len(self._tasks)) |
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finally:
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self._lock.release()
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logging.debug("All workers terminated")
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