python多进程没有锁队列范例

假设有一些任务要完成。为了完成这项任务，将使用几个过程。所以，将保持两个队列。一个包含任务，另一个包含已完成任务的日志。

然后实例化流程来完成任务。请注意，python队列类已经同步。

这意味着，我们不需要使用锁类来阻塞多个进程来访问同一个队列对象。这就是为什么，在这种情况下不需要使用锁类。

下面是将任务添加到队列中的实现，然后创建进程并启动它们，然后使用join（）完成这些进程。最后，我们将从第二个队列打印日志。

from multiprocessing import Process, Queue, current_process
import time
import queue # imported for using queue.Empty exception


def do_job(tasks_to_accomplish, tasks_that_are_done):
    while True:
        try:
            '''
                try to get task from the queue. get_nowait() function will 
                raise queue.Empty exception if the queue is empty. 
                queue(False) function would do the same task also.
            '''
            task = tasks_to_accomplish.get_nowait()
        except queue.Empty:

            break
        else:
            '''
                if no exception has been raised, add the task completion 
                message to task_that_are_done queue
            '''
            print(task)
            tasks_that_are_done.put(task + ' is done by ' + current_process().name)
            time.sleep(.5)
    return True


def main():
    number_of_task = 10
    number_of_processes = 4
    tasks_to_accomplish = Queue()
    tasks_that_are_done = Queue()
    processes = []

    for i in range(number_of_task):
        tasks_to_accomplish.put("Task no " + str(i))

    # creating processes
    for w in range(number_of_processes):
        p = Process(target=do_job, args=(tasks_to_accomplish, tasks_that_are_done))
        processes.append(p)
        p.start()

    # completing process
    for p in processes:
        p.join()

    # print the output
    while not tasks_that_are_done.empty():
        print(tasks_that_are_done.get())

    return True


if __name__ == '__main__':
    main()