python标准库介绍——31 threading 模块详解

threading 模块


(可选) ``threading`` 模块为线程提供了一个高级接口, 如 [Example 3-1 #eg-3-1] 所示. 
它源自 Java 的线程实现. 和低级的 ``thread`` 模块相同, 只有你在编译解释器时打开了线程支持才可以使用它 .

你只需要继承 //Thread// 类, 定义好 ``run`` 方法, 就可以创建一 个新的线程. 
使用时首先创建该类的一个或多个实例, 然后调用 ``start`` 方法. 这样每个实例的 
``run`` 方法都会运行在它自的线程里.
 
====Example 3-1. 使用 threading 模块====[eg-3-1]

```
File: threading-example-1.py

import threading
import time, random

class Counter:
    def _ _init_ _(self):
        self.lock = threading.Lock()
        self.value = 0

    def increment(self):
        self.lock.acquire() # critical section
        self.value = value = self.value + 1
        self.lock.release()
        return value

counter = Counter()

class Worker(threading.Thread):

    def run(self):
        for i in range(10):
            # pretend we‘re doing something that takes 10?00 ms
            value = counter.increment() # increment global counter
            time.sleep(random.randint(10, 100) / 1000.0)
            print self.getName(), "-- task", i, "finished", value

#
# try it

for i in range(10):
    Worker().start() # start a worker

*B*Thread-1 -- task 0 finished 1
Thread-3 -- task 0 finished 3
Thread-7 -- task 0 finished 8
Thread-1 -- task 1 finished 7
Thread-4 -- task 0 Thread-5 -- task 0 finished 4
finished 5
Thread-8 -- task 0 Thread-6 -- task 0 finished 9
finished 6
...
Thread-6 -- task 9 finished 98
Thread-4 -- task 9 finished 99
Thread-9 -- task 9 finished 100*b*
```

[Example 3-1 #eg-3-1] 使用了 //Lock// 对象来在全局 //Counter// 对象里创建临界区 
(critical section). 如果删除了 ``acquire`` 和 ``release`` 语句, 那么 ``Counter`` 很可能不会到达 100.