python简单的time ticker

在某些时候，我们需要精确的启动一个func，如果用time.sleep简单的轮询，会因为执行的任务阻塞，或者其他原因导致无法精确的定时执行。

例如在采集某些数据的时候，需要精确的每60秒采集一次，如果直接简单的轮询：{1：计时1，2：采集，3：计时2，4：sleep(60-计时2-计时1)}，正常的时候看起来没什么问题。

但是如果在第二步“采集”的时候阻塞超过60秒，那就会导致后续的采集延迟了。

因此需要一个新的定时器，精确的定时触发操作，不管每一步操作有没有完成，到下一个时刻都要开始触发新的操作。

如下代码，每隔4s触发do_job这个函数，在这个函数中，如果触发次数是3的倍数，则sleep 5，其他则sleep 2。

import threading
import time
import logging

logging.basicConfig(
    level=logging.DEBUG,
    format="%(asctime)s - %(levelname)s - %(message)s"
)

def do_job(count):
    logging.info("[%s] start job" % count)
    if count % 3 == 0:
        time.sleep(5)
    else:
        time.sleep(2)
    logging.info("[%s] end job" % count)

def thread_time_running(max_runs=10):
    alive_timers = []
    for i in range(0, max_runs):
        t = threading.Timer(4, do_job, [i,])
        logging.info("starting thread %d" % i)
        t.start()
        logging.info("warning thread %d" % i)
        t.join(timeout=4)
        if t.is_alive():
            alive_timers.append(t)

    for i, t in enumerate(alive_timers):
        if t.is_alive():
            t.join()

thread_time_running()

执行之后如下：

2021-03-17 20:49:50,736 - INFO - starting thread 0
2021-03-17 20:49:50,736 - INFO - warning thread 0
2021-03-17 20:49:54,742 - INFO - [0] start job
2021-03-17 20:49:54,742 - INFO - starting thread 1
2021-03-17 20:49:54,742 - INFO - warning thread 1
2021-03-17 20:49:58,748 - INFO - [1] start job
2021-03-17 20:49:58,748 - INFO - starting thread 2
2021-03-17 20:49:58,749 - INFO - warning thread 2
2021-03-17 20:49:59,746 - INFO - [0] end job
2021-03-17 20:50:00,753 - INFO - [1] end job
2021-03-17 20:50:02,754 - INFO - starting thread 3
2021-03-17 20:50:02,754 - INFO - [2] start job
2021-03-17 20:50:02,755 - INFO - warning thread 3
2021-03-17 20:50:04,755 - INFO - [2] end job
2021-03-17 20:50:06,759 - INFO - [3] start job
2021-03-17 20:50:06,759 - INFO - starting thread 4
2021-03-17 20:50:06,760 - INFO - warning thread 4
2021-03-17 20:50:10,765 - INFO - [4] start job
2021-03-17 20:50:10,765 - INFO - starting thread 5
2021-03-17 20:50:10,766 - INFO - warning thread 5
2021-03-17 20:50:11,761 - INFO - [3] end job
2021-03-17 20:50:12,770 - INFO - [4] end job
2021-03-17 20:50:14,771 - INFO - [5] start job
2021-03-17 20:50:14,771 - INFO - starting thread 6
2021-03-17 20:50:14,772 - INFO - warning thread 6
2021-03-17 20:50:16,775 - INFO - [5] end job
2021-03-17 20:50:18,774 - INFO - [6] start job
2021-03-17 20:50:18,774 - INFO - starting thread 7
2021-03-17 20:50:18,774 - INFO - warning thread 7
2021-03-17 20:50:22,777 - INFO - starting thread 8
2021-03-17 20:50:22,777 - INFO - [7] start job
2021-03-17 20:50:22,778 - INFO - warning thread 8
2021-03-17 20:50:23,776 - INFO - [6] end job
2021-03-17 20:50:24,783 - INFO - [7] end job
2021-03-17 20:50:26,783 - INFO - starting thread 9
2021-03-17 20:50:26,783 - INFO - [8] start job
2021-03-17 20:50:26,784 - INFO - warning thread 9
2021-03-17 20:50:28,786 - INFO - [8] end job
2021-03-17 20:50:30,787 - INFO - [9] start job
2021-03-17 20:50:35,790 - INFO - [9] end job