python time.sleep 花费的时间比预期的要长（多线程）

Question

我已经浏览了time.sleep()hang/delays 上的相关主题，但还没有找到答案。因此，将问题与我看到的问题一起发布。

我无权访问完整的代码。这是我可以访问并看到问题的代码 sn-p：

def my_debug(self, msg):
    logging.debug(msg, extra={'threadname':threading.currentThread().name})

while True:
    next = time.time() + INTERVAL # INTERVAL = 5
    my_debug("Triggering event")
    # some code
    # some more code
    sleep_time = max(next - time.time(), 0)
    my_debug("Sleeping for %d sec" % sleep_time)
    time.sleep(sleep_time)

这会产生：

2017-01-11 00:08:03 DEBUG MainThread Sleeping for 4 sec
2017-01-11 00:08:21 DEBUG MainThread Triggering event

显然，还有其他线程，while循环在MainThread中执行。 time.sleep 应该休眠 4 秒，而最终等待 18 秒。

我正在寻找可能导致这种行为的原因/场景。

任何帮助/指针将不胜感激。

Answer 1

这个虚构的例子可以重现你的结果。 另一个线程在计算和打印之间更改了全局sleep_time。没有锁定：

import logging
import time
import threading


INTERVAL = 5

logging.basicConfig(filename='thread.log',level=logging.DEBUG,
                    format='%(asctime)s %(message)s')

def my_debug(msg):
    logging.debug(msg, extra={'threadname':threading.currentThread().name})


class Changer(threading.Thread):

    def run(self):
        global sleep_time
        while True:
            sleep_time = 18


changer = Changer()
changer.start()


while True:
    next = time.time() + INTERVAL # INTERVAL = 5
    my_debug("Triggering event")
    # some code
    # some more code
    sleep_time = max(next - time.time(), 0)
    my_debug("Sleeping for %f sec" % sleep_time)
    time.sleep(sleep_time)

thread.log的内容：

2017-02-11 19:45:14,700 Triggering event
2017-02-11 19:45:14,701 Sleeping for 4.999720 sec
2017-02-11 19:45:32,705 Triggering event
2017-02-11 19:45:32,705 Sleeping for 4.999525 sec
2017-02-11 19:45:50,710 Triggering event
2017-02-11 19:45:50,710 Sleeping for 4.999726 sec
2017-02-11 19:46:08,714 Triggering event
2017-02-11 19:46:08,716 Sleeping for 4.997533 sec
2017-02-11 19:46:26,720 Triggering event
2017-02-11 19:46:26,725 Sleeping for 4.995042 sec
2017-02-11 19:46:44,730 Triggering event
2017-02-11 19:46:44,731 Sleeping for 4.999471 sec
2017-02-11 19:46:49,730 Triggering event
2017-02-11 19:46:49,731 Sleeping for 4.999794 sec
2017-02-11 19:47:07,736 Triggering event
2017-02-11 19:47:07,736 Sleeping for 4.999609 sec
2017-02-11 19:47:25,739 Triggering event
2017-02-11 19:47:25,739 Sleeping for 4.999751 sec

请注意，我将等待格式化为浮点数，以避免在输出中损失近一秒。