python threading中處理主進程和子線程的關係

之前用Python的多線程，總是處理不好進程和線程之間的關係。後來發現了join和setDaemon函數，才終於弄明白。下面總結一下。

1.使用join函數後，主進程會在調用join的地方等待子線程結束，然後才接著往下執行。

join使用實例如下：

[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."

運行結果如下：[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.

這裡創建了5個子線程，每個線程隨機等待1-10秒後列印退出；主線程分別等待5個子線程結束。最後結果是先顯示各個子線程，再顯示主進程的結果。

2. 如果使用的setDaemon函數，則與join相反，主進程結束的時候不會等待子線程。

setDaemon函數使用實例：

[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."

這裡設置主進程為守護進程，當主進程結束的時候，子線程被中止

運行結果如下：

[python] view plain copy

1. #python testsetDaemon.py
2. This

   is

   the end of main thread.

3、如果沒有使用join和setDaemon函數，則主進程在創建子線程後，直接運行後面的代碼，主程序一直掛起，直到子線程結束才能結束。

[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."

運行結果如下：[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.

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