5.1.1 多线程

多线程操作一般通过 threading 模块来完成，启动一个线程其实就是把线程要执行的函数传递到 Thread 类的初始化方法中，然后调用 Thread 实例的 start 方法：

import threading
from time import sleep

def think():
    print('start thinking in thread: ' + threading.current_thread().name)
    sleep(1)
    print('end thinking')

for i in range(3):
    t = threading.Thread(target = think)
    t.start()
print('Exit')
# start thinking in thread: Thread-1
# start thinking in thread: Thread-2
# start thinking in thread: Thread-3
# Exit
# end thinking
# end thinking
# end thinking

从输出结果来看，Python 的线程都是异步执行，如果要同步执行某个线程，需要调用线程的 join 方法，表示阻塞当前线程，直到整个线程退出为止：

for i in range(3):
    t = threading.Thread(target = think)
    t.start()
    t.join()
print('Exit')
# start thinking in thread: Thread-1
# end thinking
# start thinking in thread: Thread-2
# end thinking
# start thinking in thread: Thread-3
# end thinking
# Exit