python - Python:线程中的执行顺序

Question

这是用于测试Threading的代码:

import threading
import time


episode = 0
lock = threading.Lock()

class Agent(threading.Thread):
    def __init__(self, id):
        threading.Thread.__init__(self)
        self.id = id

    def run(self):
        global episode
        while episode < 5:
            with lock:
                print(
                    "{} : episode will be changed {} -> {}".format(
                        self.id,
                        episode,
                        episode+1
                    )
                )
                episode += 1
                print("{} : changed value -> {}".format(self.id, episode))
                time.sleep(1)


if __name__ == "__main__":
    agents = []
    for i in range(3):
        agents.append(Agent(i))

    for agent in agents:
        agent.start()

结果:

0 : episode will be changed 0 -> 1
0 : changed value -> 1
0 : episode will be changed 1 -> 2
0 : changed value -> 2
0 : episode will be changed 2 -> 3
0 : changed value -> 3
0 : episode will be changed 3 -> 4
0 : changed value -> 4
0 : episode will be changed 4 -> 5
0 : changed value -> 5
1 : episode will be changed 5 -> 6
1 : changed value -> 6
2 : episode will be changed 6 -> 7
2 : changed value -> 7

这是我期望的结果之一:

0 : episode will be changed 0 -> 1
0 : changed value -> 1
2 : episode will be changed 1 -> 2
2 : changed value -> 2
1 : episode will be changed 2 -> 3
1 : changed value -> 3
2 : episode will be changed 3 -> 4
2 : changed value -> 4
0 : episode will be changed 4 -> 5
0 : changed value -> 5
  .
  .

我不明白为什么线程id = 0首先一直连续出现...据我所知，线程的执行顺序是随机的，对吗？

我的代码有什么问题？

Answer 1

线程0首先启动，捕获锁，然后在按住锁的同时进入休眠状态。在 sleep 结束，由于退出with块而释放锁和再次获取锁的循环之间有很短的时间间隔，因此线程0极有可能再次获得锁...并且一次又一次，直到episode < 5最终为false。

删除time.sleep(1)上的缩进级别，使它作为循环的一部分而不是with块的一部分执行。然后线程0将在开始 sleep 之前释放该锁，其他线程几乎可以肯定在线程0处于 sleep 状态时获得了该锁(然后，它们有整整一秒钟的时间，而不是眨眼之间)。