生产者与消费者-条件变量

演示条件变量同步的经典问题是生产者与消费者问题：假设有一群生产者(Producer)和一群消费者（Consumer）通过一个市场来交互产品。生产者的”策略“是如果市场上剩余的产品少于1000个，那么就生产100个产品放到市场上；而消费者的”策略“是如果市场上剩余产品的数量多余100个，那么就消费3个产品。用Condition解决生产者与消费者问题的代码如下：

import threading
import time

class Producer(threading.Thread):
    def run(self):
        global count
        while True:
            if con.acquire():
                if count > 1000:
                    con.wait()
                else:
                    count += 100
                    msg = self.name+' produce 100, count=' + str(count)
                    print msg
                    con.notify()
                con.release()
            time.sleep(1)

class Consumer(threading.Thread):
    def run(self):
        global count
        while True:
            if con.acquire():
                if count < 100:
                    con.wait()
                else:
                    count -= 3
                    msg = self.name+' consume 3, count='+str(count)
                    print msg
                    con.notify()
                con.release()
            time.sleep(1)


if __name__ == '__main__':

    count = 500
    con = threading.Condition()

    for i in range(2):
        p = Producer()
        p.start()

    for i in range(5):
        c = Consumer()
        c.start()