如何启动和停止线程？

Question

对不起老问题.我澄清了.如何用我糟糕的线程类启动一个停止线程？

编辑:它在循环中,我想在代码的开头再次重新启动它.如何进行start-stop-restart-stop-restart？

我的课:

import threading

class Concur(threading.Thread):
    def __init__(self):
        self.stopped = False
        threading.Thread.__init__(self)

    def run(self):
        i = 0
        while not self.stopped:
            time.sleep(1)
            i = i + 1

在主代码中,我想要:

inst = Concur()

while conditon:
    inst.start()

    #after some operation
    inst.stop()
    #some other operation

Answer 1

您实际上无法停止然后重新启动线程,因为start()在run()方法终止后无法再次调用它.但是,您可以通过使用threading.Condition变量来停止并稍后恢复执行,以避免在检查或更改其运行状态时出现并发问题.

threading.Condition对象有一个关联的threading.Lock对象和方法来等待它被释放,并在发生时通知任何等待的线程.这是一个从您的问题中的代码派生的示例,它显示了这一点.在示例代码中,我将Condition变量作为Thread子类实例的一部分,以更好地封装实现,并避免需要引入其他全局变量:

from __future__ import print_function
import threading
import time

class Concur(threading.Thread):
    def __init__(self):
        super(Concur, self).__init__()
        self.iterations = 0
        self.daemon = True  # Allow main to exit even if still running.
        self.paused = True  # Start out paused.
        self.state = threading.Condition()

    def run(self):
        self.resume()
        while True:
            with self.state:
                if self.paused:
                    self.state.wait()  # Block execution until notified.
            # Do stuff.
            time.sleep(.1)
            self.iterations += 1

    def resume(self):
        with self.state:
            self.paused = False
            self.state.notify()  # Unblock self if waiting.

    def pause(self):
        with self.state:
            self.paused = True  # Block self.


class Stopwatch(object):
    """ Simple class to measure elapsed times. """
    def start(self):
        """ Establish reference point for elapsed time measurements. """
        self.start_time = time.time()
        return self.start_time

    @property
    def elapsed_time(self):
        """ Seconds since started. """
        try:
            start_time = self.start_time
        except AttributeError:  # Wasn't explicitly started.
            start_time = self.start()

        return time.time() - start_time


MAX_RUN_TIME = 5  # Seconds.
concur = Concur()
stopwatch = Stopwatch()

print('Running for {} seconds...'.format(MAX_RUN_TIME))
concur.start()
while stopwatch.elapsed_time < MAX_RUN_TIME:
    concur.resume()
    # ... do some concurrent operations.
    concur.pause()
    # Do some other stuff...

# Show Concur thread executed.
print('concur.iterations: {}'.format(concur.iterations))

Answer 2

这是David Heffernan的想法充实.下面的示例运行1秒,然后停止1秒,然后运行1秒,依此类推.

import time
import threading
import datetime as DT
import logging
logger = logging.getLogger(__name__)

def worker(cond):
    i = 0
    while True:
        with cond:
            cond.wait()
            logger.info(i)
            time.sleep(0.01)
            i += 1

logging.basicConfig(level=logging.DEBUG,
                    format='[%(asctime)s %(threadName)s] %(message)s',
                    datefmt='%H:%M:%S')

cond = threading.Condition()
t = threading.Thread(target=worker, args=(cond, ))
t.daemon = True
t.start()

start = DT.datetime.now()
while True:
    now = DT.datetime.now()
    if (now-start).total_seconds() > 60: break
    if now.second % 2:
        with cond:
            cond.notify()

Answer 3

的实现stop()如下所示：

def stop(self):
    self.stopped = True

如果您想重新启动，那么您只需创建一个新实例并启动它即可。

while conditon:
    inst = Concur()
    inst.start()

    #after some operation
    inst.stop()
    #some other operation

的文档Thread清楚地表明该方法只能为start()该类的每个实例调用一次。

如果您想暂停和恢复线程，那么您需要使用条件变量。