之前用python的多執行緒，總是處理不好程序和執行緒之間的關係。後來發現了join和setDaemon函式，才終於弄明白。下面總結一下。

1.使用join函式後，主程序會在呼叫join的地方等待子執行緒結束，然後才接著往下執行。

join使用例項如下：

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."
 

# 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.

這裡建立了5個子執行緒，每個執行緒隨機等待1-10秒後列印退出；主執行緒分別等待5個子執行緒結束。最後結果是先顯示各個子執行緒，再顯示主程序的結果。

2. 如果使用的setDaemon函式，則與join相反，主程序結束的時候不會等待子執行緒。

setDaemon函式使用例項：

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."
 

執行結果如下：

#python testsetDaemon.py 
This is the end of main thread.

3、如果沒有使用join和setDaemon函式，則主程序在建立子執行緒後，直接執行後面的程式碼，主程式一直掛起，直到子執行緒結束才能結束。

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."

# 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.