Python队列在获取下一个项目之前等待线程

Question

我有一个队列，当它们被添加到它时，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以在后台执行操作，以便程序可以去做其他事情。

但是，我在队列中的每个项目上调用的函数只是启动线程然后完成执行，而不管它启动的线程是否完成。因此，在程序处理完最后一项之前，循环将转到队列中的下一项。

这是更好地展示我正在尝试做的事情的代码：

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.

一些注意事项：

这一切都在 PyGTK 应用程序中运行。 'SomeThread' 操作完成后，它会向 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。

你应该做的是：

1. 将线程实现为一个类
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。如果它看到它被清除，它就会返回。为此覆盖 threading.Thread.join 以检查事件，然后自行调用 Thread.join
3. 为了允许 (2)，从 Queue 块读取一些小的超时。这样，您的线程对终止请求的“响应时间”将是超时，并且 OTOH 不会完成 CPU 阻塞

这里有一些来自套接字客户端线程的代码，它与阻塞队列有同样的问题：

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)

注意self.alive 和run 中的循环。