两个线程交替打印数字

题目表述

编写两个线程，一个打印偶数、一个打印奇数；要求按顺序打印。

解答

Python 中线程同步可以通过锁(Lock)、信号量(Semaphore)、条件(Condition)、事件机制(Event)、队列（Queue）来实现。

代码实现

# 两个线程，一个打印偶数、一个打印奇数；按顺序打印
import threading


lock1 = threading.Lock()
lock2 = threading.Lock()
lock2.acquire()


def print_odd(upper=100):
    """打印奇数"""
    for i in range(1, upper, 2):
        lock1.acquire()
        print(i)
        lock2.release()


def print_even(upper=100):
    """打印偶数"""
    for i in range(2, upper, 2):
        lock2.acquire()
        print(i)
        lock1.release()


if __name__ == "__main__":
    t1 = threading.Thread(target=print_odd)
    t2 = threading.Thread(target=print_even)
    t1.start()
    t2.start()
    t1.join()
    t2.join()

# 两个线程，一个打印偶数、一个打印奇数；按顺序打印
import threading


sema1 = threading.Semaphore(1)
sema2 = threading.Semaphore(0)


def print_odd(upper=100):
    """打印奇数"""
    for i in range(1, upper, 2):
        sema1.acquire()
        sema2.release()
        print(i)


def print_even(upper=100):
    """打印偶数"""
    for i in range(2, upper, 2):
        sema2.acquire()
        sema1.release()
        print(i)


if __name__ == "__main__":
    t1 = threading.Thread(target=print_odd)
    t2 = threading.Thread(target=print_even)
    t1.start()
    t2.start()
    t1.join()
    t2.join()

# 两个线程，一个打印偶数、一个打印奇数；按顺序打印
import threading

condition = threading.Condition()
current = 0


def print_odd(upper=100):
    """打印奇数"""
    global current
    for i in range(1, upper, 2):
        with condition:
            if current == 1:
                condition.wait()
            current = 1
            print(i)
            condition.notify()


def print_even(upper=100):
    """打印偶数"""
    global current
    for i in range(2, upper, 2):
        with condition:
            if current == 0:
                condition.wait()
            current = 0
            print(i)
            condition.notify()


if __name__ == "__main__":
    t1 = threading.Thread(target=print_odd)
    t2 = threading.Thread(target=print_even)
    t1.start()
    t2.start()
    t1.join()
    t2.join()

# 两个线程，一个打印偶数、一个打印奇数；按顺序打印
import threading

event1 = threading.Event()
event2 = threading.Event()
event1.set()


def print_odd(upper=100):
    """打印奇数"""
    for i in range(1, upper, 2):
        event1.wait()
        print(i)
        event1.clear()
        event2.set()


def print_even(upper=100):
    """打印偶数"""
    for i in range(2, upper, 2):
        event2.wait()
        print(i)
        event2.clear()
        event1.set()


if __name__ == "__main__":
    t1 = threading.Thread(target=print_odd)
    t2 = threading.Thread(target=print_even)
    t1.start()
    t2.start()
    t1.join()
    t2.join()

"""
两个线程，一个打印偶数、一个打印奇数；按顺序打印
队列实现
"""
import threading
from queue import Queue

odd_queue = Queue(1)
even_queue = Queue(1)


def print_odd(upper=100):
    """打印奇数"""
    odd_queue.put(1)
    while True:
        num = odd_queue.get()
        print(num)
        even_queue.put(num + 1)
        if num >= upper:
            return


def print_even(upper=100):
    """打印偶数"""
    while True:
        num = even_queue.get()
        print(num)
        odd_queue.put(num + 1)
        if num >= upper:
            return


if __name__ == "__main__":
    t1 = threading.Thread(target=print_odd)
    t2 = threading.Thread(target=print_even)
    t1.start()
    t2.start()
    t1.join()
    t2.join()