python多线程之t.setDaemon(True) 和 t.join()
0.目录
1.参考
2.结论
(1)通过 t.setDaemon(True) 将子线程设置为守护进程(默认False),主线程代码执行完毕后,python程序退出,无需理会守护子线程的状态。
(2) t.join() 用于阻塞主线程,可以想象成将某个子线程的执行过程插入(join)到主线程的时间线上,主线程的后续代码延后执行。注意和 t.start() 分开写在两个for循环中。
(3)第一个for循环同时启动了所有子线程,随后在第二个for循环中执行t.join() ,主线程实际被阻塞的总时长==其中执行时间最长的一个子线程。
3.验证过程
1.参考
C:\Program Files\Anaconda2\Lib\threading.py
def daemon(self):
"""A boolean value indicating whether this thread is a daemon thread (True) or not (False). This must be set before start() is called, otherwise RuntimeError is
raised. Its initial value is inherited from the creating thread; the
main thread is not a daemon thread and therefore all threads created in
the main thread default to daemon = False. The entire Python program exits when no alive non-daemon threads are
left. """
def join(self, timeout=None):
"""Wait until the thread terminates. This blocks the calling thread until the thread whose join() method is
called terminates -- either normally or through an unhandled exception
or until the optional timeout occurs. When the timeout argument is present and not None, it should be a
floating point number specifying a timeout for the operation in seconds
(or fractions thereof). As join() always returns None, you must call
isAlive() after join() to decide whether a timeout happened -- if the
thread is still alive, the join() call timed out. When the timeout argument is not present or None, the operation will
block until the thread terminates. A thread can be join()ed many times. join() raises a RuntimeError if an attempt is made to join the current
thread as that would cause a deadlock. It is also an error to join() a
thread before it has been started and attempts to do so raises the same
exception. """
2.结论
(1)通过 t.setDaemon(True) 将子线程设置为守护进程(默认False),主线程代码执行完毕后,python程序退出,无需理会守护子线程的状态。
(2) t.join() 用于阻塞主线程,可以想象成将某个子线程的执行过程插入(join)到主线程的时间线上,主线程的后续代码延后执行。注意和 t.start() 分开写在两个for循环中。
(3)第一个for循环同时启动了所有子线程,随后在第二个for循环中执行t.join() ,主线程实际被阻塞的总时长==其中执行时间最长的一个子线程。
3.验证过程
(1)子线程默认为【非守护线程】,主线程代码执行完毕,各子线程继续运行,直到所有【非守护线程】结束,python程序退出。
#!usr/bin/env python
#coding:utf-8
import time
import random
import logging import thread
import threading
from Queue import Queue lock = threading.Lock() #'function-call ownership'
rlock = threading.RLock() #thread ownership def get_logger():
logger = logging.getLogger("threading_example")
logger.setLevel(logging.DEBUG) # fh = logging.FileHandler("d:/threading.log")
fh = logging.StreamHandler()
fmt = '%(asctime)s - %(threadName)-10s - %(levelname)s - %(message)s'
formatter = logging.Formatter(fmt)
fh.setFormatter(formatter) logger.addHandler(fh)
return logger
logger = get_logger()
################################# class MyThread(threading.Thread):
def __init__(self, number):
threading.Thread.__init__(self)
self.number = number
def run(self):
for i in range(2):
logger.debug(i)
time.sleep(self.number) def main():
logger.debug('MainThread Start')
threads = [MyThread(3-i) for i in range(3)] for t in threads:
t.start() logger.debug('MainThread End') if __name__ == '__main__':
main()
输出:
2017-08-15 17:04:12,512 - MainThread - DEBUG - MainThread Start
2017-08-15 17:04:12,512 - Thread-1 - DEBUG - 0
2017-08-15 17:04:12,513 - Thread-2 - DEBUG - 0
2017-08-15 17:04:12,513 - Thread-3 - DEBUG - 0
2017-08-15 17:04:12,513 - MainThread - DEBUG - MainThread End
2017-08-15 17:04:13,513 - Thread-3 - DEBUG - 1
2017-08-15 17:04:14,513 - Thread-2 - DEBUG - 1
2017-08-15 17:04:15,513 - Thread-1 - DEBUG - 1
(2) t.setDaemon(True), 主线程代码执行完毕,直接退出python程序,无需理会【守护】子线程的状态。
def main():
logger.debug('MainThread Start')
threads = [MyThread(3-i) for i in range(3)] for t in threads:
t.setDaemon(True) #将子线程设置为守护进程
t.start() logger.debug('MainThread End')
输出:
2017-08-15 17:06:20,822 - MainThread - DEBUG - MainThread Start
2017-08-15 17:06:20,822 - Thread-1 - DEBUG - 0
2017-08-15 17:06:20,823 - Thread-2 - DEBUG - 0
2017-08-15 17:06:20,823 - MainThread - DEBUG - MainThread End
2017-08-15 17:06:20,823 - Thread-3 - DEBUG - 0
(3)错误用法: d t1.join()阻塞了主线程的for循环,t1结束后才执行t2.start()...实际就变成了单线程顺序执行。
def main():
logger.debug('MainThread Start')
threads = [MyThread(3-i) for i in range(3)] for t in threads:
t.start()
t.join()
logger.debug('{} start() join() activeCount: {}'.format(t.getName(), threading.activeCount())) logger.debug('MainThread End')
输出:
2017-08-15 17:17:38,219 - MainThread - DEBUG - MainThread Start
2017-08-15 17:17:38,230 - Thread-1 - DEBUG - 0
2017-08-15 17:17:41,230 - Thread-1 - DEBUG - 1
2017-08-15 17:17:44,232 - MainThread - DEBUG - Thread-1 start() join() activeCount: 1
2017-08-15 17:17:44,232 - Thread-2 - DEBUG - 0
2017-08-15 17:17:46,232 - Thread-2 - DEBUG - 1
2017-08-15 17:17:48,233 - MainThread - DEBUG - Thread-2 start() join() activeCount: 1
2017-08-15 17:17:48,233 - Thread-3 - DEBUG - 0
2017-08-15 17:17:49,234 - Thread-3 - DEBUG - 1
2017-08-15 17:17:50,234 - MainThread - DEBUG - Thread-3 start() join() activeCount: 1
2017-08-15 17:17:50,234 - MainThread - DEBUG - MainThread End
(4)异常用法:只对for循环的最后一个子线程执行了t.join() ,如果该子线程的执行时长不是所有子线程中最久的,可能达不到预期效果。
def main():
logger.debug('MainThread Start')
# threads = [MyThread(3-i) for i in range(3)]
threads = [MyThread((3-i)*2) for i in range(3)] #修改了等待时间 for t in threads:
t.start() logger.debug('MainThread ing')
# for t in threads:
t.join()
logger.debug('{} is_alive: {} join() activeCount: {}'.format(t.getName(), t.is_alive(), threading.activeCount()))
logger.debug('MainThread End')
输出:
2017-08-15 18:18:10,924 - MainThread - DEBUG - MainThread Start
2017-08-15 18:18:10,927 - Thread-1 - DEBUG - 0
2017-08-15 18:18:10,930 - Thread-2 - DEBUG - 0
2017-08-15 18:18:10,931 - Thread-3 - DEBUG - 0
2017-08-15 18:18:10,931 - MainThread - DEBUG - MainThread ing
2017-08-15 18:18:12,931 - Thread-3 - DEBUG - 1
2017-08-15 18:18:14,931 - Thread-2 - DEBUG - 1
2017-08-15 18:18:14,931 - MainThread - DEBUG - Thread-3 is_alive: False join() activeCount: 3
2017-08-15 18:18:14,931 - MainThread - DEBUG - MainThread End
2017-08-15 18:18:16,928 - Thread-1 - DEBUG - 1
(5)正常用法:第二个for循环保证每一个子线程都执行了t.join(), 虽然t1运行结束后才执行t2.join(), 但是第一个for循环已经启动了所有子线程,所以主线程实际被阻塞的总时长==其中执行时间最长的一个子线程。
def main():
logger.debug('MainThread Start')
# threads = [MyThread(3-i) for i in range(3)]
threads = [MyThread((i+1)*2) for i in range(3)] #修改了等待时间 for t in threads:
t.start() logger.debug('MainThread ing')
for t in threads:
logger.debug('{} is_alive: {} join() activeCount: {}'.format(t.getName(), t.is_alive(), threading.activeCount()))
t.join()
logger.debug('MainThread End')
输出:
2017-08-15 17:30:00,499 - MainThread - DEBUG - MainThread Start
2017-08-15 17:30:00,499 - Thread-1 - DEBUG - 0
2017-08-15 17:30:00,500 - Thread-2 - DEBUG - 0
2017-08-15 17:30:00,500 - Thread-3 - DEBUG - 0
2017-08-15 17:30:00,500 - MainThread - DEBUG - MainThread ing
2017-08-15 17:30:00,500 - MainThread - DEBUG - Thread-1 is_alive: True join() activeCount: 4
2017-08-15 17:30:02,500 - Thread-1 - DEBUG - 1
2017-08-15 17:30:04,500 - Thread-2 - DEBUG - 1
2017-08-15 17:30:04,500 - MainThread - DEBUG - Thread-2 is_alive: True join() activeCount: 3
2017-08-15 17:30:06,500 - Thread-3 - DEBUG - 1
2017-08-15 17:30:08,503 - MainThread - DEBUG - Thread-3 is_alive: True join() activeCount: 2
2017-08-15 17:30:12,500 - MainThread - DEBUG - MainThread End
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