Python多线程编程

原文


运行几个线程和同时运行几个不同的程序类似,它有以下好处:

  •  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。
一个线程的顺序是:启动,执行和停止。有一个指令指针跟踪线程正在运行的上下文在哪里。

  •  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
除了方法,threading模块有Thread类实现threading。Thread类提供的方法如下:

  •  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
在你创建新的Thread子类以后,你可以创建它的一个实例,然后引用start()来开启一个新线程,它会依次调用call方法。


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
例子:
#!/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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Python多线程编程

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