python threading中处理主进程和子线程的关系

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：

[python] view plain copy

1. import time
2. import random
3. import threading
5. class worker(threading.Thread):
6. def __init__(self):
7. threading.Thread.__init__(self)
8. def run(self):
9. t = random.randint(1,10)
10. time.sleep(t)
11. print "This is " + self.getName() + ";I sleep %d second."%(t)
13. tsk = []
14. for i in xrange(0,5):
15. time.sleep(0.1)
16. thread = worker()
17. thread.start()
18. tsk.append(thread)
19. for tt in tsk:
20. tt.join()
21. print "This is the end of main thread."

运行结果如下：[python] view plain copy

1. # python testjoin.py
2. This is Thread-3;I sleep 2 second.
3. This is Thread-1;I sleep 4 second.
4. This is Thread-2;I sleep 7 second.
5. This is Thread-4;I sleep 7 second.
6. This is Thread-5;I sleep 7 second.
7. 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：

[python] view plain copy

1. import time
2. import random
3. import threading
5. class worker(threading.Thread):
6. def __init__(self):
7. threading.Thread.__init__(self)
8. def run(self):
9. t = random.randint(1,10)
10. time.sleep(t)
11. print "This is " + self.getName() + ";I sleep %d second."%(t)
13. tsk = []
14. for i in xrange(0,5):
15. time.sleep(0.1)
16. thread = worker()
17. thread.setDaemon(True)
18. thread.start()
19. tsk.append(thread)
20. 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] view plain copy

1. #python testsetDaemon.py
2. 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。

[python] view plain copy

1. import time
2. import random
3. import threading
5. class worker(threading.Thread):
6. def __init__(self):
7. threading.Thread.__init__(self)
8. def run(self):
9. t = random.randint(1,10)
10. time.sleep(t)
11. print "This is " + self.getName() + ";I sleep %d second."%(t)
13. tsk = []
14. for i in xrange(0,5):
15. time.sleep(0.1)
16. thread = worker()
17. thread.start()
18. tsk.append(thread)
19. print "This is the end of main thread."

运行结果如下：[python] view plain copy

1. # python testthread.py
2. This is the end of main thread.
3. This is Thread-4;I sleep 1 second.
4. This is Thread-3;I sleep 7 second.
5. This is Thread-5;I sleep 7 second.
6. This is Thread-1;I sleep 10 second.
7. This is Thread-2;I sleep 10 second.