Python队列在获取下一个项目之前等待线程

Question

我有一个队列，当项目添加到队列中时，它总是需要准备好处理它们。在队列中的每个项目上运行的函数创建并启动线程在后台执行操作，以便程序可以执行其他操作。

但是，我对队列中的每个项目调用的函数只是启动线程，然后完成执行，无论它启动的线程是否完成。因此，在程序处理完最后一项之前，循环将移至队列中的下一项。

下面的代码可以更好地演示我想要做的事情：

queue = Queue.Queue()
t = threading.Thread(target=worker)
t.start()

def addTask():
    queue.put(SomeObject())

def worker():
    while True:
        try:
            # If an item is put onto the queue, immediately execute it (unless 
            # an item on the queue is still being processed, in which case wait 
            # for it to complete before moving on to the next item in the queue)
            item = queue.get()
            runTests(item)
            # I want to wait for 'runTests' to complete before moving past this point
        except Queue.Empty, err:
            # If the queue is empty, just keep running the loop until something 
            # is put on top of it.
            pass

def runTests(args):
    op_thread = SomeThread(args)
    op_thread.start()
    # My problem is once this last line 't.start()' starts the thread, 
    # the 'runTests' function completes operation, but the operation executed
    # by some thread is not yet done executing because it is still running in
    # the background. I do not want the 'runTests' function to actually complete
    # execution until the operation in thread t is done executing.
    """t.join()"""
    # I tried putting this line after 't.start()', but that did not solve anything.
    # I have commented it out because it is not necessary to demonstrate what 
    # I am trying to do, but I just wanted to show that I tried it.

一些注释：

这一切都在 PyGTK 应用程序中运行。一旦“SomeThread”操作完成，它就会向 GUI 发送回调以显示操作结果。

我不知道这对我遇到的问题有多大影响，但我认为这可能很重要。

Answer 1

Python 线程的一个基本问题是你不能直接杀死它们——它们必须同意死亡。

您应该做的是：

1. 将线程实现为类
2. 添加一个 threading.Event 成员，join 方法会清除该成员，并且线程的主循环偶尔会检查该成员。如果它发现它被清除，它就会返回。对于此重写，threading.Thread.join 检查事件，然后对其自身调用 Thread.join
3. 要允许 (2)，请从 Queue 进行读取code> 块有一些小的超时。这样你的线程对终止请求的“响应时间”将是超时，并且不会发生 CPU 阻塞

这是来自我的套接字客户端线程的一些代码，它与队列阻塞有相同的问题：

class SocketClientThread(threading.Thread):
    """ Implements the threading.Thread interface (start, join, etc.) and
        can be controlled via the cmd_q Queue attribute. Replies are placed in
        the reply_q Queue attribute.
    """
    def __init__(self, cmd_q=Queue.Queue(), reply_q=Queue.Queue()):
        super(SocketClientThread, self).__init__()
        self.cmd_q = cmd_q
        self.reply_q = reply_q
        self.alive = threading.Event()
        self.alive.set()
        self.socket = None

        self.handlers = {
            ClientCommand.CONNECT: self._handle_CONNECT,
            ClientCommand.CLOSE: self._handle_CLOSE,
            ClientCommand.SEND: self._handle_SEND,
            ClientCommand.RECEIVE: self._handle_RECEIVE,
        }

    def run(self):
        while self.alive.isSet():
            try:
                # Queue.get with timeout to allow checking self.alive
                cmd = self.cmd_q.get(True, 0.1)
                self.handlers[cmd.type](cmd)
            except Queue.Empty as e:
                continue

    def join(self, timeout=None):
        self.alive.clear()
        threading.Thread.join(self, timeout)

Note self .alive 和 run 中的循环。