如何启动和停止线程？

Question

对不起，老问题。我已经澄清了。我如何用我可怜的线程类开始停止线程？

编辑：它在循环中，我想在代码开头再次重新启动它。我如何启动停止重新启动？

我的班级：

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，我希望：

inst = Concur()

while conditon:
    inst.start()

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

Answer 1

Stop（）的实现如下：

def stop(self):
    self.stopped = True

如果您想重新启动，那么您可以创建一个新实例并启动它。

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

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

Thread的留档清楚地表明，类的每个实例只能调用start（）方法一次。

如果要暂停并恢复线程，则需要使用条件变量。

Answer 2

这就是大卫·赫弗南的想法。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

您实际上不能停止然后重新启动一个线程，因为您不能在它的run（）方法终止后再次调用它的start（）方法。但是，您可以使用线程使一个停止，然后恢复执行。条件变量，以避免检查或更改其运行状态时出现并发问题。

线程。条件对象具有关联的线程。锁定对象和方法以等待它被释放，并在发生这种情况时通知所有等待的线程。下面是一个从您问题中的代码派生的示例，它显示了这一点。在示例代码中，我将条件变量作为线程子类实例的一部分，以更好地封装实现并避免引入其他全局变量：

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

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


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

    @property
    def elapsed_time(self):
        """ Seconds since started. """
        try:
            return time.time() - self.start_time
        except AttributeError:  # Wasn't explicitly started.
            self.start_time = time.time()
            return 0



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()
    # Can also do other concurrent operations here...
    concur.pause()
    # Do some other stuff...

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