本文通过实例解析Python中的主进程与子线程关系，重点介绍join函数和setDaemon函数的使用。join函数使得主进程等待子线程结束后再继续执行，而setDaemon则使主进程不等待子线程，直接结束。
https://blog.youkuaiyun.com/oatnehc/article/details/50616835
https://www.cnblogs.com/ArsenalfanInECNU/p/8989770.html
之前用python的多线程，总是处理不好进程和线程之间的关系。后来发现了join和setDaemon函数，才终于弄明白。下面总结一下。
1.使用join函数后，主进程会在调用join的地方等待子线程结束，然后才接着往下执行。
join使用实例如下：
-
import time -
import random -
import threading -
class worker(threading.Thread): -
def __init__(self): -
threading.Thread.__init__(self) -
def run(self): -
t = random.randint(1,10) -
time.sleep(t) -
print "This is " + self.getName() + ";I sleep %d second."%(t) -
tsk = [] -
for i in xrange(0,5): -
time.sleep(0.1) -
thread = worker() -
thread.start() -
tsk.append(thread) -
for tt in tsk: -
tt.join() -
print "This is the end of main thread."
运行结果如下：
-
# python testjoin.py -
This is Thread-3;I sleep 2 second. -
This is Thread-1;I sleep 4 second. -
This is Thread-2;I sleep 7 second. -
This is Thread-4;I sleep 7 second. -
This is Thread-5;I sleep 7 second. -
This is the end of main thread.
这里创建了5个子线程，每个线程随机等待1-10秒后打印退出；主线程分别等待5个子线程结束。最后结果是先显示各个子线程，再显示主进程的结果。
2. 如果使用的setDaemon函数，则与join相反，主进程结束的时候不会等待子线程。
setDaemon函数使用实例：
-
import time -
import random -
import threading -
class worker(threading.Thread): -
def __init__(self): -
threading.Thread.__init__(self) -
def run(self): -
t = random.randint(1,10) -
time.sleep(t) -
print "This is " + self.getName() + ";I sleep %d second."%(t) -
tsk = [] -
for i in xrange(0,5): -
time.sleep(0.1) -
thread = worker() -
thread.setDaemon(True) -
thread.start() -
tsk.append(thread) -
print "This is the end of main thread."
这里设置主进程为守护进程，当主进程结束的时候，子线程被中止
运行结果如下：
-
#python testsetDaemon.py -
This is the end of main thread.
3、如果没有使用join和setDaemon函数，则主进程在创建子线程后，直接运行后面的代码，主程序一直挂起，直到子线程结束才能结束。
-
import time -
import random -
import threading -
class worker(threading.Thread): -
def __init__(self): -
threading.Thread.__init__(self) -
def run(self): -
t = random.randint(1,10) -
time.sleep(t) -
print "This is " + self.getName() + ";I sleep %d second."%(t) -
tsk = [] -
for i in xrange(0,5): -
time.sleep(0.1) -
thread = worker() -
thread.start() -
tsk.append(thread) -
print "This is the end of main thread."
运行结果如下：
-
# python testthread.py -
This is the end of main thread. -
This is Thread-4;I sleep 1 second. -
This is Thread-3;I sleep 7 second. -
This is Thread-5;I sleep 7 second. -
This is Thread-1;I sleep 10 second. -
This is Thread-2;I sleep 10 second.
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