Python 中的Lock与RLock

 

如果多个线程共同对某个数据修改，则可能出现不可预料的结果，为了保证数据的正确性，需要对多个线程进行同步,使用 Thread 对象的 Lock 和 Rlock 可以实现简单的线程同步，这两个对象都有 acquire 方法和 release 方法,分别用来获取和释放锁

 

启动3个线程对count进行操作

import threading

count = 0
def print_time(threadName):
    global  count
    c = 0
    while(c<100):
        c+=1
        count +=1
        print("{0}:set count to {1}".format(threadName,count))

try:
    threading.Thread( target=print_time, args=("Thread-1", ) ).start()
    threading.Thread( target=print_time, args=("Thread-2", ) ).start()
    threading.Thread( target=print_time, args=("Thread-3", ) ).start()
except Exception as e:
    print("Error: unable to start thread")

结果“ 每个thread对count进行改动期间while(c<100)，有其它的thread插入进来改动count

 

 

 

通过threading.Lock() 实现，通过Lock的acquire()和release()函数来控制加锁和解锁，使用简单得方法 with实现

import threading
lock = threading.Lock()
count = 0
def print_time(threadName):
    global  count
    c = 0
    with lock:
        while(c<100):
            c+=1
            count +=1
            print("{0}:set count to {1}".format(threadName,count))

try:
    threading.Thread( target=print_time, args=("Thread-1", ) ).start()
    threading.Thread( target=print_time, args=("Thread-2", ) ).start()
    threading.Thread( target=print_time, args=("Thread-3", ) ).start()
except Exception as e:
    print("Error: unable to start thread")　

 结果

 

 通过threading.Rlock() 实现

import threading
rlock = threading.RLock()
count = 0
def print_time(threadName):
    global  count
    c = 0
    with rlock:
        while(c<100):
            c+=1
            count +=1
            print("{0}:set count to {1}".format(threadName,count))

try:
    threading.Thread( target=print_time, args=("Thread-1", ) ).start()
    threading.Thread( target=print_time, args=("Thread-2", ) ).start()
    threading.Thread( target=print_time, args=("Thread-3", ) ).start()
except Exception as e:
    print("Error: unable to start thread")　

j结果

 

 

Lock和Rlock的区别

import threading
lock = threading.Lock() #Lock对象
lock.acquire()
lock.acquire()  #产生了死琐。
lock.release()
lock.release()

　　

 

import threading
lock = threading.RLock() #Lock对象
lock.acquire()
lock.acquire()  程序不会堵塞
lock.release()
lock.release()

 

 

Locks	RLocks
A Lock object can not be acquired again by any thread unless it is released by the thread which which is accessing the shared resource. 一个lock被释放前不能被其他线程获得acquire	An RLock object can be acquired numerous times by any thread. 一个Rlock可以被其他任意线程获得
A Lock object can be released by any thread. 一个lock可以被其他线程释放	An RLock object can only be released by the thread which acquired it. Rlock只能被获得他的线程释放
A Lock object can be owned by one lock被一个线程占有	An RLock object can be owned by many threads Rlock可以被其他线程获得
Execution of a Lock object is faster. lock的运行速度快	Execution of an RLock object is slower than a Lock object 运行速度比lock慢

　　

这两种琐的主要区别是：RLock允许在同一线程中被多次acquire。而Lock却不允许这种情况。注意：如果使用RLock，那么acquire和release必须成对出现，即调用了n次acquire，必须调用n次的release才能真正释放所占用的琐