11.python Concurrency Primer (part6 semaphore semaphore)

One, what is the semaphore.

The semaphore is also a lock.

The primary use of semaphores is to control the concurrency of threads, Boundedsemaphore or semaphore manage a built-in counter, each time the acquire () method is called, the counter-1, each time the release () method is called, the internal counter +1.

However, it is important to note that the counter inside the semaphore cannot be less than 0! When the counter inside is equal to 0, the thread is locked into a blocking state until the other thread calls the release method.

The only difference between Boundedsemaphore and semaphore is that the former will check that the value of the counter exceeds the initial value of the counter when it calls release (), and throws an exception if it is exceeded.

Ii. examples of semaphore usage.

#!/usr/local/bin/python2.7

#-*-Coding:utf-8-*-

Import threading

Import time

Semaphore = Threading. Semaphore (5) #设置同一次只能最多有5个线程通过.

def func ():

If Semaphore.acquire ():

Print Threading.currentthread (). GetName () + "semaphore"

Time.sleep (2)

Semaphore.release ()

For _ in range (20):

T1 = Threading. Thread (Target=func)

T1.start ()

Output Run Result:

Thread-1semaphore

Thread-2semaphore

Thread-3semaphore

Thread-4semaphore

Thread-5semaphore

Thread-6semaphore

Thread-7semaphore

Thread-8semaphore

Thread-9semaphore

Thread-10semaphore

Thread-13semaphore

Thread-11semaphore

Thread-12semaphore

Thread-14semaphore

Thread-15semaphore

Thread-17semaphore

Thread-20semaphore

Thread-19semaphore

Thread-18semaphore

Thread-16semaphore

A maximum of 5 threads were released at a time, a bit like the concept of parking spaces.

Three, the difference between the signal volume and the recursive lock.

Personal Understanding ~ The difference between the semaphore and the recursive lock is not, in the semaphore, the same lock, multiple threads can operate the same shared data, the recursive lock before the lock is freed a thread can only manipulate one shared data.

This article is from the "Rebirth" blog, make sure to keep this source http://suhaozhi.blog.51cto.com/7272298/1925456

11.python Concurrency Primer (part6 semaphore semaphore)