Python多线程编程
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Python多线程编程
- 一个进程内的多个线程和主线程分享相同的数据空间,比分开不同的过程更容易分享信息或者彼此通信。
- 线程有时叫做轻量化过程,而且他们不要求更多的内存开支;它们比过程便宜。
- 它可以被抢占(中断)
- 它能暂时被挂起(也叫做休眠),而别的线程在运行--这也叫做yielding(让步)。
开始一个新线程:
要生成一个线程,需要调用在thread模块中方法如下:thread.start_new_thread ( function, args[, kwargs] )
这种函数调用提供了创建新线程快速和有效的方法,适用于Windows和Linux。
方法立即返回,而子线程启动并调用函数,函数的参数为传递的args列表。当函数返回时,线程结束。
在这里,args是参数元组;调用函数而不传递任何参数使用空的元组。kwargs是可选的关键字参数字典。
例子:
#!/usr/bin/python
- import thread
- import time
- # Define a function for the thread
- def print_time( threadName, delay):
- count = 0
- while count < 5:
- time.sleep(delay)
- count += 1
- print "%s: %s" % ( threadName, time.ctime(time.time()) )
- # Create two threads as follows
- try:
- thread.start_new_thread( print_time, ("Thread-1", 2, ) )
- thread.start_new_thread( print_time, ("Thread-2", 4, ) )
- except:
- print "Error: unable to start thread"
- while 1:
- pass
上述代码执行时,产生以下结果:
Thread-1: Thu Jan 22 15:42:17 2009
Thread-1: Thu Jan 22 15:42:19 2009
Thread-2: Thu Jan 22 15:42:19 2009
Thread-1: Thu Jan 22 15:42:21 2009
Thread-2: Thu Jan 22 15:42:23 2009
Thread-1: Thu Jan 22 15:42:23 2009
Thread-1: Thu Jan 22 15:42:25 2009
Thread-2: Thu Jan 22 15:42:27 2009
Thread-2: Thu Jan 22 15:42:31 2009
Thread-2: Thu Jan 22 15:42:35 2009
尽管对于低级别的线程,它是非常有效的,然而thread模块与较新的线程模块相比,其功能还是非常有限的。
Threading模块:
与前一节讨论的thread模块相比,从Python2.4开始包含的较新的threading模块,为线程提供了更多强大、高级的支持。threading模块包含了thread模块中所有的方法,并提供一些其余的方法:
- threading.activeCount():返回激活的线程对象的数目
- theading.currentThread():返回调用者的线程控制中线程对象的数目
- threading.enumerate(): 返回当前活动的线程对象列表
- run():线程的入口点
- start():调用run方法启动线程
- join(time):等待线程结束
- isAlive():检查一个线程是否仍旧在执行
- getName():返回线程的名字
- setName():设置一个线程的名字
使用Threading模块创建线程:
要使用threading模块实现一个新线程,你得先如下做:- 定义Thread类的一个子类。
- 重写__init__(self,[,args])方法以增加额外的参数
- 然后,重写run(self[,args])方法以实现线程启动后要做的事情
例子:
- #!/usr/bin/python
- import threading
- import time
- exitFlag = 0
- class myThread (threading.Thread):
- def __init__(self, threadID, name, counter):
- threading.Thread.__init__(self)
- self.threadID = threadID
- self.name = name
- self.counter = counter
- def run(self):
- print "Starting " + self.name
- print_time(self.name, self.counter, 5)
- print "Exiting " + self.name
- def print_time(threadName, delay, counter):
- while counter:
- if exitFlag:
- thread.exit()
- time.sleep(delay)
- print "%s: %s" % (threadName, time.ctime(time.time()))
- counter -= 1
- # Create new threads
- thread1 = myThread(1, "Thread-1", 1)
- thread2 = myThread(2, "Thread-2", 2)
- # Start new Threads
- thread1.start()
- thread2.start()
- print "Exiting Main Thread"
上述代码执行后,它会产出如下结果:
Starting Thread-1
Starting Thread-2
Exiting Main Thread
Thread-1: Thu Mar 21 09:10:03 2013
Thread-1: Thu Mar 21 09:10:04 2013
Thread-2: Thu Mar 21 09:10:04 2013
Thread-1: Thu Mar 21 09:10:05 2013
Thread-1: Thu Mar 21 09:10:06 2013
Thread-2: Thu Mar 21 09:10:06 2013
Thread-1: Thu Mar 21 09:10:07 2013
Exiting Thread-1
Thread-2: Thu Mar 21 09:10:08 2013
Thread-2: Thu Mar 21 09:10:10 2013
Thread-2: Thu Mar 21 09:10:12 2013
Exiting Thread-2
同步线程:
Python提供的threading模块包括一个易于实现的锁定机制,以允许你同步线程。创建一个新锁通过调用Lock()实现,它也返回这个新锁。
新锁对象的accquire(blocking)方法,用来强制线程同步运行。可选的blocking参数使你能够控制线程是否请求锁。
如果blocking设置为0,线程在不能获取锁时立即返回0值;而blocking设置为1时,线程获取锁以后返回1值。如果blocking设置为1,线程将会阻塞,一直等到锁释放。
新锁对象的release()方法用来释放不再需要的锁。
例子:
- #!/usr/bin/python
- import threading
- import time
- class myThread (threading.Thread):
- def __init__(self, threadID, name, counter):
- threading.Thread.__init__(self)
- self.threadID = threadID
- self.name = name
- self.counter = counter
- def run(self):
- print "Starting " + self.name
- # Get lock to synchronize threads
- threadLock.acquire()
- print_time(self.name, self.counter, 3)
- # Free lock to release next thread
- threadLock.release()
- def print_time(threadName, delay, counter):
- while counter:
- time.sleep(delay)
- print "%s: %s" % (threadName, time.ctime(time.time()))
- counter -= 1
- threadLock = threading.Lock()
- threads = []
- # Create new threads
- thread1 = myThread(1, "Thread-1", 1)
- thread2 = myThread(2, "Thread-2", 2)
- # Start new Threads
- thread1.start()
- thread2.start()
- # Add threads to thread list
- threads.append(thread1)
- threads.append(thread2)
- # Wait for all threads to complete
- for t in threads:
- t.join()
- print "Exiting Main Thread"
当上述代码执行后,它产生以下结果:
Starting Thread-1
Starting Thread-2
Thread-1: Thu Mar 21 09:11:28 2013
Thread-1: Thu Mar 21 09:11:29 2013
Thread-1: Thu Mar 21 09:11:30 2013
Thread-2: Thu Mar 21 09:11:32 2013
Thread-2: Thu Mar 21 09:11:34 2013
Thread-2: Thu Mar 21 09:11:36 2013
Exiting Main Thread
多线程优先级 队列:
Queue模块允许你创建一个新的队列对象,以盛放一定数量的项目。控制Queue有以下方法:
- get():从队列移除一个项目并返回它
- put():把项目放入队列
- qsize():返回当前队列中项目的数量
- empty():如果队列为空,返回True,反之为False
- full():如果队列满了返回True,反之为False
- #!/usr/bin/python
- import Queue
- import threading
- import time
- exitFlag = 0
- class myThread (threading.Thread):
- def __init__(self, threadID, name, q):
- threading.Thread.__init__(self)
- self.threadID = threadID
- self.name = name
- self.q = q
- def run(self):
- print "Starting " + self.name
- process_data(self.name, self.q)
- print "Exiting " + self.name
- def process_data(threadName, q):
- while not exitFlag:
- queueLock.acquire()
- if not workQueue.empty():
- data = q.get()
- queueLock.release()
- print "%s processing %s" % (threadName, data)
- else:
- queueLock.release()
- time.sleep(1)
- threadList = ["Thread-1", "Thread-2", "Thread-3"]
- nameList = ["One", "Two", "Three", "Four", "Five"]
- queueLock = threading.Lock()
- workQueue = Queue.Queue(10)
- threads = []
- threadID = 1
- # Create new threads
- for tName in threadList:
- thread = myThread(threadID, tName, workQueue)
- thread.start()
- threads.append(thread)
- threadID += 1
- # Fill the queue
- queueLock.acquire()
- for word in nameList:
- workQueue.put(word)
- queueLock.release()
- # Wait for queue to empty
- while not workQueue.empty():
- pass
- # Notify threads it's time to exit
- exitFlag = 1
- # Wait for all threads to complete
- for t in threads:
- t.join()
- print "Exiting Main Thread"
当上述代码执行后,它产生以下结果:
Starting Thread-1
Starting Thread-2
Starting Thread-3
Thread-1 processing One
Thread-2 processing Two
Thread-3 processing Three
Thread-1 processing Four
Thread-2 processing Five
Exiting Thread-3
Exiting Thread-1
Exiting Thread-2
Exiting Main Thread
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