Question

我正在尝试创建一个在后台执行操作的线程。我需要能够在需要时有效地“暂停”它，并在以后再次“恢复”它。此外，如果线程在我“暂停”它时正在做某事，它应该让调用线程等到它完成它正在做的事情。

我对Python中的多线程很新，所以我还没有那么远。

除了让调用线程等待，如果在我的线程正在执行某些操作时调用了暂停，我所做的一切几乎都做了。

以下是我在代码中尝试实现的内容概述：

import threading, time

class Me(threading.Thread):
    def __init__(self):
        threading.Thread.__init__(self)
        #flag to pause thread
        self.paused = False

    def run(self):
        while True:
            if not self.paused:
                #thread should do the thing if
                #not paused
                print 'do the thing'
                time.sleep(5)

    def pause(self):
        self.paused = True
        #this is should make the calling thread wait if pause() is
        #called while the thread is 'doing the thing', until it is
        #finished 'doing the thing'

    #should just resume the thread
    def resume(self):
        self.paused = False

我认为我基本上需要一个锁定机制，但是在同一个线程中？

Answer 1

Conditions can be used for this

以下是填充骨架的示例：

class Me(threading.Thread):
    def __init__(self):
        threading.Thread.__init__(self)
        #flag to pause thread
        self.paused = False
        # Explicitly using Lock over RLock since the use of self.paused
        # break reentrancy anyway, and I believe using Lock could allow
        # one thread to pause the worker, while another resumes; haven't
        # checked if Condition imposes additional limitations that would 
        # prevent that. In Python 2, use of Lock instead of RLock also
        # boosts performance.
        self.pause_cond = threading.Condition(threading.Lock())

    def run(self):
        while True:
            with self.pause_cond:
                while self.paused:
                    self.pause_cond.wait()

                #thread should do the thing if
                #not paused
                print 'do the thing'
            time.sleep(5)

    def pause(self):
        self.paused = True
        # If in sleep, we acquire immediately, otherwise we wait for thread
        # to release condition. In race, worker will still see self.paused
        # and begin waiting until it's set back to False
        self.pause_cond.acquire()

    #should just resume the thread
    def resume(self):
        self.paused = False
        # Notify so thread will wake after lock released
        self.pause_cond.notify()
        # Now release the lock
        self.pause_cond.release()

希望有所帮助。

Answer 2

使用threading.Event而不是布尔变量，并为忙碌状态添加另一个事件：

def __init__(self):
    ...
    self.can_run = threading.Event()
    self.thing_done = threading.Event()
    self.thing_done.set()
    self.can_run.set()    

def run(self):
    while True:
        self.can_run.wait()
        try:
            self.thing_done.clear()
            print 'do the thing'
        finally:
            self.thing_done.set()

def pause(self):
    self.can_run.clear()
    self.thing_done.wait()

def resume(self):
    self.can_run.set()

编辑：之前的回答是错误的，我修复了它并更改了变量名称

我可以暂停和恢复的线程？

2 个答案: