如何启动和停止线程

Question

如何使用我糟糕的线程类启动和停止线程？

它处于循环中，我想在代码开头再次重新启动它。 我怎样才能开始-停止-重启-停止-重启？

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

您实际上不能停止然后重新启动线程，因为在它的run()方法终止后您不能再次调用它的start()方法。 但是，您可以暂停一次，然后通过使用threading.Condition变量恢复其执行，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额外的全局变量：

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))

Answer 2

这是大卫赫弗南的想法的充实。 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

stop()的实现如下所示：

def stop(self):
    self.stopped = True

如果要重新启动，则只需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的文档清楚地表明start()方法只能为类的每个实例调用一次。

如果要暂停和恢复线程，则需要使用条件变量。