python多线程 简明例子...
时间：2010-08-08 来源：rj03hou
综述
多线程是程序设计中的一个重要方面，尤其是在服务器Deamon程序方面。无论何种系统，线程调度的开销都比传统的进程要快得多。
Python可以方便地支持多线程。可以快速创建线程、互斥锁、信号量等等元素，支持线程读写同步互斥。美中不足的是，Python的运行在Python虚拟机上，创建的多线程可能是虚拟的线程，需要由Python虚拟机来轮询调度，这大大降低了Python多线程的可用性。希望高版本的Python可以解决这个问题，发挥多CPU的最大效率。
网上有些朋友说要获得真正多CPU的好处，有两种方法：
1.可以创建多个进程而不是线程，进程数和cpu一样多。
2.使用Jython 或 IronPython，可以得到真正的多线程。 闲话少说，下面看看Python如何建立线程 Python线程创建 使用threading模块的 Thread类 类接口如下 class Thread( group=None, target=None, name=None, args=(), kwargs={}) 需要关注的参数是target和args. target 是需要子线程运行的目标函数，args是函数的参数，以tuple的形式传递。 以下代码创建一个指向函数worker 的子线程 def worker(a_tid,a_account):
...
th = threading.Thread(target=worker,args=(i,acc) ) ; 启动这个线程 th.start() 等待线程返回 threading.Thread.join(th)
或者th.join() 如果你可以对要处理的数据进行很好的划分，而且线程之间无须通信，那么你可以使用：创建=》运行=》回收的方式编写你的多线程程序。但是如果线程之间需要访问共同的对象，则需要引入互斥锁或者信号量对资源进行互斥访问。 下面讲讲如何创建互斥锁 创建锁
g_mutex = threading.Lock()
....
使用锁
for ... :
#锁定，从下一句代码到释放前互斥访问
g_mutex.acquire()
a_account.deposite(1)
#释放
g_mutex.release() 最后，模拟一个公交地铁IC卡缴车费的多线程程序 有10个读卡器，每个读卡器收费器每次扣除用户一块钱进入总账中，每读卡器每天一共被刷10000000次。账户原有100块。所以最后的总账应该为10000100。先不使用互斥锁来进行锁定（注释掉了锁定代码），看看后果如何。 import time,datetime
import threading
def worker(a_tid,a_account):
global g_mutex
print "Str " , a_tid, datetime.datetime.now()
for i in range(1000000):
#g_mutex.acquire()
a_account.deposite(1)
#g_mutex.release()
print "End " , a_tid , datetime.datetime.now()
class Account:
def __init__ (self, a_base ):
self.m_amount=a_base
def deposite(self,a_amount):
self.m_amount+=a_amount
def withdraw(self,a_amount):
self.m_amount-=a_amount
if __name__ == "__main__":
global g_mutex
count = 0
dstart = datetime.datetime.now()
print "Main Thread Start At: " , dstart
#init thread_pool
thread_pool = []
#init mutex
g_mutex = threading.Lock()
# init thread items
acc = Account(100)
for i in range(10):
th = threading.Thread(target=worker,args=(i,acc) ) ;
thread_pool.append(th)
# start threads one by one
for i in range(10):
thread_pool[i].start()
#collect all threads
for i in range(10):
threading.Thread.join(thread_pool[i])
dend = datetime.datetime.now()
print "count=",acc.m_amount
print "Main Thread End at: " ,dend , " time span " , dend-dstart; 注意，先不用互斥锁进行临界段访问控制，运行结果如下： Main Thread Start At: 2009-01-13 00:17:55.296000
Str 0 2009-01-13 00:17:55.312000
Str 1 2009-01-13 00:17:55.453000
Str 2 2009-01-13 00:17:55.484000
Str 3 2009-01-13 00:17:55.531000
Str 4 2009-01-13 00:17:55.562000
Str 5 2009-01-13 00:17:55.609000
Str 6 2009-01-13 00:17:55.640000
Str 7 2009-01-13 00:17:55.687000
Str 8 2009-01-13 00:17:55.718000
Str 9 2009-01-13 00:17:55.781000
End 0 2009-01-13 00:18:06.250000
End 1 2009-01-13 00:18:07.500000
End 4 2009-01-13 00:18:07.531000
End 2 2009-01-13 00:18:07.562000
End 3 2009-01-13 00:18:07.593000
End 9 2009-01-13 00:18:07.609000
End 7 2009-01-13 00:18:07.640000
End 8 2009-01-13 00:18:07.671000
End 5 2009-01-13 00:18:07.687000
End 6 2009-01-13 00:18:07.718000
count= 3434612
Main Thread End at: 2009-01-13 00:18:07.718000 time span 0:00:12.422000 从结果看到，程序确实是多线程运行的。但是由于没有对对象Account进行互斥访问，所以结果是错误的，只有3434612，比原预计少了很多。 把上面阴影部分代码的注释打开，运行结果如下 Main Thread Start At: 2009-01-13 00:26:12.156000
Str 0 2009-01-13 00:26:12.156000
Str 1 2009-01-13 00:26:12.390000
Str 2 2009-01-13 00:26:12.437000
Str 3 2009-01-13 00:26:12.468000
Str 4 2009-01-13 00:26:12.515000
Str 5 2009-01-13 00:26:12.562000
Str 6 2009-01-13 00:26:12.593000
Str 7 2009-01-13 00:26:12.640000
Str 8 2009-01-13 00:26:12.671000
Str 9 2009-01-13 00:26:12.718000
End 0 2009-01-13 00:27:01.781000
End 1 2009-01-13 00:27:05.890000
End 5 2009-01-13 00:27:06.046000
End 7 2009-01-13 00:27:06.078000
End 4 2009-01-13 00:27:06.109000
End 2 2009-01-13 00:27:06.140000
End 6 2009-01-13 00:27:06.156000
End 8 2009-01-13 00:27:06.187000
End 3 2009-01-13 00:27:06.203000
End 9 2009-01-13 00:27:06.234000
count= 10000100
Main Thread End at: 2009-01-13 00:27:06.234000 time span 0:00:54.078000 这次可以看到，结果正确了。运行时间比不进行互斥多了很多，需要花54秒才能运行（我机器烂，没钱更新，呵呵），不过这也是同步的代价，没办法。
2.使用Jython 或 IronPython，可以得到真正的多线程。 闲话少说，下面看看Python如何建立线程 Python线程创建 使用threading模块的 Thread类 类接口如下 class Thread( group=None, target=None, name=None, args=(), kwargs={}) 需要关注的参数是target和args. target 是需要子线程运行的目标函数，args是函数的参数，以tuple的形式传递。 以下代码创建一个指向函数worker 的子线程 def worker(a_tid,a_account):
...
th = threading.Thread(target=worker,args=(i,acc) ) ; 启动这个线程 th.start() 等待线程返回 threading.Thread.join(th)
或者th.join() 如果你可以对要处理的数据进行很好的划分，而且线程之间无须通信，那么你可以使用：创建=》运行=》回收的方式编写你的多线程程序。但是如果线程之间需要访问共同的对象，则需要引入互斥锁或者信号量对资源进行互斥访问。 下面讲讲如何创建互斥锁 创建锁
g_mutex = threading.Lock()
....
使用锁
for ... :
#锁定，从下一句代码到释放前互斥访问
g_mutex.acquire()
a_account.deposite(1)
#释放
g_mutex.release() 最后，模拟一个公交地铁IC卡缴车费的多线程程序 有10个读卡器，每个读卡器收费器每次扣除用户一块钱进入总账中，每读卡器每天一共被刷10000000次。账户原有100块。所以最后的总账应该为10000100。先不使用互斥锁来进行锁定（注释掉了锁定代码），看看后果如何。 import time,datetime
import threading
def worker(a_tid,a_account):
global g_mutex
print "Str " , a_tid, datetime.datetime.now()
for i in range(1000000):
#g_mutex.acquire()
a_account.deposite(1)
#g_mutex.release()
print "End " , a_tid , datetime.datetime.now()
class Account:
def __init__ (self, a_base ):
self.m_amount=a_base
def deposite(self,a_amount):
self.m_amount+=a_amount
def withdraw(self,a_amount):
self.m_amount-=a_amount
if __name__ == "__main__":
global g_mutex
count = 0
dstart = datetime.datetime.now()
print "Main Thread Start At: " , dstart
#init thread_pool
thread_pool = []
#init mutex
g_mutex = threading.Lock()
# init thread items
acc = Account(100)
for i in range(10):
th = threading.Thread(target=worker,args=(i,acc) ) ;
thread_pool.append(th)
# start threads one by one
for i in range(10):
thread_pool[i].start()
#collect all threads
for i in range(10):
threading.Thread.join(thread_pool[i])
dend = datetime.datetime.now()
print "count=",acc.m_amount
print "Main Thread End at: " ,dend , " time span " , dend-dstart; 注意，先不用互斥锁进行临界段访问控制，运行结果如下： Main Thread Start At: 2009-01-13 00:17:55.296000
Str 0 2009-01-13 00:17:55.312000
Str 1 2009-01-13 00:17:55.453000
Str 2 2009-01-13 00:17:55.484000
Str 3 2009-01-13 00:17:55.531000
Str 4 2009-01-13 00:17:55.562000
Str 5 2009-01-13 00:17:55.609000
Str 6 2009-01-13 00:17:55.640000
Str 7 2009-01-13 00:17:55.687000
Str 8 2009-01-13 00:17:55.718000
Str 9 2009-01-13 00:17:55.781000
End 0 2009-01-13 00:18:06.250000
End 1 2009-01-13 00:18:07.500000
End 4 2009-01-13 00:18:07.531000
End 2 2009-01-13 00:18:07.562000
End 3 2009-01-13 00:18:07.593000
End 9 2009-01-13 00:18:07.609000
End 7 2009-01-13 00:18:07.640000
End 8 2009-01-13 00:18:07.671000
End 5 2009-01-13 00:18:07.687000
End 6 2009-01-13 00:18:07.718000
count= 3434612
Main Thread End at: 2009-01-13 00:18:07.718000 time span 0:00:12.422000 从结果看到，程序确实是多线程运行的。但是由于没有对对象Account进行互斥访问，所以结果是错误的，只有3434612，比原预计少了很多。 把上面阴影部分代码的注释打开，运行结果如下 Main Thread Start At: 2009-01-13 00:26:12.156000
Str 0 2009-01-13 00:26:12.156000
Str 1 2009-01-13 00:26:12.390000
Str 2 2009-01-13 00:26:12.437000
Str 3 2009-01-13 00:26:12.468000
Str 4 2009-01-13 00:26:12.515000
Str 5 2009-01-13 00:26:12.562000
Str 6 2009-01-13 00:26:12.593000
Str 7 2009-01-13 00:26:12.640000
Str 8 2009-01-13 00:26:12.671000
Str 9 2009-01-13 00:26:12.718000
End 0 2009-01-13 00:27:01.781000
End 1 2009-01-13 00:27:05.890000
End 5 2009-01-13 00:27:06.046000
End 7 2009-01-13 00:27:06.078000
End 4 2009-01-13 00:27:06.109000
End 2 2009-01-13 00:27:06.140000
End 6 2009-01-13 00:27:06.156000
End 8 2009-01-13 00:27:06.187000
End 3 2009-01-13 00:27:06.203000
End 9 2009-01-13 00:27:06.234000
count= 10000100
Main Thread End at: 2009-01-13 00:27:06.234000 time span 0:00:54.078000 这次可以看到，结果正确了。运行时间比不进行互斥多了很多，需要花54秒才能运行（我机器烂，没钱更新，呵呵），不过这也是同步的代价，没办法。
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