| #!/usr/bin/env python |
| # Copyright 2014 the V8 project authors. All rights reserved. |
| # Use of this source code is governed by a BSD-style license that can be |
| # found in the LICENSE file. |
| |
| from multiprocessing import Event, Process, Queue |
| |
| class NormalResult(): |
| def __init__(self, result): |
| self.result = result |
| self.exception = False |
| self.break_now = False |
| |
| |
| class ExceptionResult(): |
| def __init__(self): |
| self.exception = True |
| self.break_now = False |
| |
| |
| class BreakResult(): |
| def __init__(self): |
| self.exception = False |
| self.break_now = True |
| |
| |
| def Worker(fn, work_queue, done_queue, done): |
| """Worker to be run in a child process. |
| The worker stops on two conditions. 1. When the poison pill "STOP" is |
| reached or 2. when the event "done" is set.""" |
| try: |
| for args in iter(work_queue.get, "STOP"): |
| if done.is_set(): |
| break |
| try: |
| done_queue.put(NormalResult(fn(*args))) |
| except Exception, e: |
| print(">>> EXCEPTION: %s" % e) |
| done_queue.put(ExceptionResult()) |
| except KeyboardInterrupt: |
| done_queue.put(BreakResult()) |
| |
| |
| class Pool(): |
| """Distributes tasks to a number of worker processes. |
| New tasks can be added dynamically even after the workers have been started. |
| Requirement: Tasks can only be added from the parent process, e.g. while |
| consuming the results generator.""" |
| |
| # Factor to calculate the maximum number of items in the work/done queue. |
| # Necessary to not overflow the queue's pipe if a keyboard interrupt happens. |
| BUFFER_FACTOR = 4 |
| |
| def __init__(self, num_workers): |
| self.num_workers = num_workers |
| self.processes = [] |
| self.terminated = False |
| |
| # Invariant: count >= #work_queue + #done_queue. It is greater when a |
| # worker takes an item from the work_queue and before the result is |
| # submitted to the done_queue. It is equal when no worker is working, |
| # e.g. when all workers have finished, and when no results are processed. |
| # Count is only accessed by the parent process. Only the parent process is |
| # allowed to remove items from the done_queue and to add items to the |
| # work_queue. |
| self.count = 0 |
| self.work_queue = Queue() |
| self.done_queue = Queue() |
| self.done = Event() |
| |
| def imap_unordered(self, fn, gen): |
| """Maps function "fn" to items in generator "gen" on the worker processes |
| in an arbitrary order. The items are expected to be lists of arguments to |
| the function. Returns a results iterator.""" |
| try: |
| gen = iter(gen) |
| self.advance = self._advance_more |
| |
| for w in xrange(self.num_workers): |
| p = Process(target=Worker, args=(fn, |
| self.work_queue, |
| self.done_queue, |
| self.done)) |
| self.processes.append(p) |
| p.start() |
| |
| self.advance(gen) |
| while self.count > 0: |
| result = self.done_queue.get() |
| self.count -= 1 |
| if result.exception: |
| # Ignore items with unexpected exceptions. |
| continue |
| elif result.break_now: |
| # A keyboard interrupt happened in one of the worker processes. |
| raise KeyboardInterrupt |
| else: |
| yield result.result |
| self.advance(gen) |
| finally: |
| self.terminate() |
| |
| def _advance_more(self, gen): |
| while self.count < self.num_workers * self.BUFFER_FACTOR: |
| try: |
| self.work_queue.put(gen.next()) |
| self.count += 1 |
| except StopIteration: |
| self.advance = self._advance_empty |
| break |
| |
| def _advance_empty(self, gen): |
| pass |
| |
| def add(self, args): |
| """Adds an item to the work queue. Can be called dynamically while |
| processing the results from imap_unordered.""" |
| self.work_queue.put(args) |
| self.count += 1 |
| |
| def terminate(self): |
| if self.terminated: |
| return |
| self.terminated = True |
| |
| # For exceptional tear down set the "done" event to stop the workers before |
| # they empty the queue buffer. |
| self.done.set() |
| |
| for p in self.processes: |
| # During normal tear down the workers block on get(). Feed a poison pill |
| # per worker to make them stop. |
| self.work_queue.put("STOP") |
| |
| for p in self.processes: |
| p.join() |
| |
| # Drain the queues to prevent failures when queues are garbage collected. |
| try: |
| while True: self.work_queue.get(False) |
| except: |
| pass |
| try: |
| while True: self.done_queue.get(False) |
| except: |
| pass |