Python multiprocessing.Queue在put和get上的死锁 [英] Python multiprocessing.Queue deadlocks on put and get

问题描述

我遇到这段代码的死锁问题：

I'm having deadlock problems with this piece of code:

def _entropy_split_parallel(data_train, answers_train, weights):
    CPUS = 1 #multiprocessing.cpu_count()
    NUMBER_TASKS = len(data_train[0])
    processes = []

    multi_list = zip(data_train, answers_train, weights)

    task_queue = multiprocessing.Queue()
    done_queue = multiprocessing.Queue()

    for feature_index in xrange(NUMBER_TASKS):
        task_queue.put(feature_index)

    for i in xrange(CPUS):
        process = multiprocessing.Process(target=_worker, 
                args=(multi_list, task_queue, done_queue))
        processes.append(process)
        process.start()

    min_entropy = None
    best_feature = None
    best_split = None
    for i in xrange(NUMBER_TASKS):
        entropy, feature, split = done_queue.get()
        if (entropy < min_entropy or min_entropy == None) and entropy != None:
            best_feature = feature
            best_split = split

    for i in xrange(CPUS):
        task_queue.put('STOP')

    for process in processes:
        process.join()

    return best_feature, best_split


def _worker(multi_list, task_queue, done_queue):
    feature_index = task_queue.get()
    while feature_index != 'STOP':
        result = _entropy_split3(multi_list, feature_index)
        done_queue.put(result)
        feature_index = task_queue.get()

当我运行我的程序时，通过 _entropy_split_parallel ，但最终死锁。父进程阻塞在 done_queue.get（），并且工作进程阻塞 done_queue.put（） 。由于队列在这种情况下总是为空，因此期望在 get 上阻塞。我不明白是为什么工人阻塞在 put ，因为队列显然不是满的（它是空的！）。我尝试了 block 和 timeout 关键字参数，但得到相同的结果。

When I run my program, it works fine for several runs through _entropy_split_parallel, but eventually deadlocks. The parent process is blocking on done_queue.get(), and the worker process is blocking on done_queue.put(). Since the queue is always empty when this happens, blocking on get is expected. What I don't understand is why the worker is blocking on put, since the queue is obviously not full (it's empty!). I've tried the block and timeout keyword arguments, but get the same result.

我使用多处理反向端口，因为我被Python 2.5困扰。

I'm using the multiprocessing backport, since I'm stuck with Python 2.5.

编辑：看起来像我也有与多处理模块提供的示例之一的死锁问题。这是从底部的第三个例子这里死锁只是似乎发生，如果我调用测试方法多次。例如，将脚本底部更改为：

It looks like I'm also getting deadlock issues with one of the examples provided with the multiprocessing module. It's the third example from the bottom here. The deadlocking only seems to occur if I call the test method many times. For example, changing the bottom of the script to this:

if __name__ == '__main__':
    freeze_support()
    for x in xrange(1000):
        test()

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编辑：我知道这是一个老问题，但测试表明这不再是与Python 2.7的Windows上的问题。我会尝试Linux并回报。

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I know this is an old question, but testing shows that this is no longer a problem on windows with Python 2.7. I will try Linux and report back.

推荐答案

Python的新版本已经消失了，后端的问题。无论如何，它不再是一个问题。

This problem went away with newer versions of Python, so I'm assuming it was a problem with the backport. Anyways, it's no longer an issue.

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