我們前面提到了進(jìn)程是由若干線程組成的兔魂，一個(gè)進(jìn)程至少有一個(gè)線程栈妆。
多線程優(yōu)點(diǎn)：

• 在一個(gè)進(jìn)程中的多線程和主線程分享相同的數(shù)據(jù)空間扛吞，因此可以很容易的分享信息和通信初肉。
• 線程有時(shí)候被稱為輕量級(jí)進(jìn)程酷鸦，并且他們不需要太多的內(nèi)存開銷，比起進(jìn)程更低成本牙咏。

一個(gè)線程都有一個(gè)開始,一個(gè)執(zhí)行序列和一個(gè)結(jié)論臼隔。它有一個(gè)指令指針用在目前運(yùn)行在的上下文中跟蹤。

• 他可以被搶占（中斷）
• 當(dāng)在其他線程運(yùn)行的時(shí)候可以被臨時(shí)掛起
  Python的標(biāo)準(zhǔn)庫(kù)提供了兩個(gè)模塊：thread和threading妄壶，thread是低級(jí)模塊摔握，threading是高級(jí)模塊，對(duì)thread進(jìn)行了封裝丁寄。絕大多數(shù)情況下氨淌，我們只需要使用threading這個(gè)高級(jí)模塊。

#!/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:
            threadName.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"

運(yùn)行結(jié)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

也可以如下使用：

import time, threading
# 新線程執(zhí)行的代碼:
def loop():
    print 'thread %s is running...' % threading.current_thread().name
    n = 0
    while n < 5:
        n = n + 1
        print 'thread %s >>> %s' % (threading.current_thread().name, n)
        time.sleep(1)
    print 'thread %s ended.' % threading.current_thread().name
def create_thread():
    # 啟動(dòng)一個(gè)線程就是把一個(gè)函數(shù)傳入并創(chuàng)建Thread實(shí)例伊磺，然后調(diào)用start()開始執(zhí)行
    # 由于任何進(jìn)程默認(rèn)就會(huì)啟動(dòng)一個(gè)線程盛正，我們把該線程稱為主線程，主線程又可以啟動(dòng)新的線程
    print 'thread %s is running...' % threading.current_thread().name
    t = threading.Thread(target=loop, name='LoopThread')
    t.start()
    t.join()
    print 'thread %s ended.' % threading.current_thread().name
if __name__ == '__main__':
    create_thread()
    # more_threading()

運(yùn)行結(jié)果：

thread MainThread is running...
thread LoopThread is running...
thread LoopThread >>> 1
thread LoopThread >>> 2
thread LoopThread >>> 3
thread LoopThread >>> 4
thread LoopThread >>> 5
thread LoopThread ended.
thread MainThread ended.

鎖

#!/usr/bin/python
import threading
import time
class myThread_Lock (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_second(self.name, self.counter, 3)
        # Free lock to release next thread
        threadLock.release()
def print_time_second(threadName, delay, counter):
  while counter:
      time.sleep(delay)
      print "%s: %s" % (threadName, time.ctime(time.time()))
      counter -= 1
def test_lock():
    threads = []
    # Create new threads
    thread1 = myThread_Lock(1, "Thread-1", 1)
    thread2 = myThread_Lock(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"
if __name__ == "__main__":
    # test()
    test_lock()

運(yùn)行結(jié)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

再來(lái)

#!/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"

運(yùn)行結(jié)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

再來(lái)：

import time, threading
balance = 0
lock = threading.Lock()
def change_it(n):
    # 先存后取奢浑，結(jié)果應(yīng)該為0:
    global balance
    balance = balance + n
    balance = balance - n
def run_thread_uselock(n):
    # 當(dāng)多個(gè)線程同時(shí)執(zhí)行l(wèi)ock.acquire()時(shí)蛮艰，只有一個(gè)線程能成功地獲取鎖，然后繼續(xù)執(zhí)行代碼，其他線程就繼續(xù)等待直到獲得鎖為止壤蚜。
    for i in range(100000):
        # 先要獲取鎖:
        lock.acquire()
        try:
            # 放心地改吧:
            change_it(n)
        finally:
            # 改完了一定要釋放鎖:
            lock.release()
def run_thread(n):
    for i in range(100000):
        change_it(n)
def more_threading():
    # 多線程和多進(jìn)程最大的不同在于即寡，多進(jìn)程中，同一個(gè)變量袜刷，各自有一份拷貝存在于每個(gè)進(jìn)程中聪富，互不影響，
    # 而多線程中著蟹，所有變量都由所有線程共享墩蔓，所以，任何一個(gè)變量都可以被任何一個(gè)線程修改萧豆，
    # 因此奸披，線程之間共享數(shù)據(jù)最大的危險(xiǎn)在于多個(gè)線程同時(shí)改一個(gè)變量，把內(nèi)容給改亂了涮雷。
    # t1 = threading.Thread(target=run_thread, args=(5,))
    # t2 = threading.Thread(target=run_thread, args=(8,))
    t3 = threading.Thread(target=run_thread_uselock, args=(5,))
    t4 = threading.Thread(target=run_thread_uselock, args=(8,))
    # t1.start()
    # t2.start()
    # t1.join()
    # t2.join()
    t3.start()
    t4.start()
    t3.join()
    t4.join()
    print balance # result may not be 0,but it should be 0 in normal.
if __name__ == '__main__':
    # create_thread()
    more_threading()

運(yùn)行結(jié)果：0