08_线程间通信 ITC

1.线程间的通信方式

1.共享全局变量

2.线程队列(queue)

3.信号量(Semaphore)

2.共享全局变量进行通信

from threading import Thread
import time

g_nums = [11,22,33]

def work1(nums):
    nums.append(44)
    print("----in work1---",nums)

def work2(nums):
    #延时一会,保证t1线程中的事情做完
    time.sleep(1)
    print("----in work2---",nums)

t1 = Thread(target=work1, args=(g_nums,))
t1.start()
t2 = Thread(target=work2, args=(g_nums,))
t2.start()

3.共享全局变量的资源竞争

# 多个线程同时对同一个全局变量操作,会出现资源竞争问题,从而数据结果会不正确
import threading
import time

g_num = 0

def work1(num):
    global g_num
    for i in range(num):
        g_num += 1
    print("----in work1, g_num is %d---" % g_num)

def work2(num):
    global g_num
    for i in range(num):
        g_num += 1
    print("----in work2, g_num is %d---" % g_num)

print("---线程创建之前g_num is %d---" % g_num)

t1 = threading.Thread(target=work1, args=(1000000,))
t1.start()
t2 = threading.Thread(target=work2, args=(1000000,))
t2.start()

while len(threading.enumerate()) != 1:
    time.sleep(1)

print("2个线程对同一个全局变量操作之后的最终结果是:%s" % g_num)

4.线程队列queue.Queue-生产者消费者模式

from threading import Thread
import queue
from time import sleep

# 生产者
class Producer(Thread):
    def run(self):
        count = 0
        while True:
            if q.qsize() < 50:
                for i in range(3):
                    count += 1
                    msg = "产品%d" % count  # 将产品放入队列
                    q.put(msg)
                    # print("生产了: %s 还有%s个" % (msg, q.qsize()))
            sleep(1)

# 消费者
class Customer(Thread):
    def run(self):
        while True:
            if q.qsize() > 20:
                for i in range(2):
                    msg = q.get()  # 从仓库中拿货
                    print("消耗了: %s 还有%s个" % (msg, q.qsize()))
            sleep(1)

def main():
    # 创建一个队列仓库
    global q
    q = queue.Queue()
    # 创建2个生产
    for i in range(2):
        p = Producer()
        p.start()
    # 创建3个消费
    for i in range(3):
        c = Customer()
        c.start()

if __name__ == "__main__":
    main()
"""执行结果
    消耗了: 产品1 还有20个
    消耗了: 产品2 还有22个
    消耗了: 产品3 还有24个
    消耗了: 产品1 还有23个
    消耗了: 产品2 还有25个
    消耗了: 产品3 还有24个
    消耗了: 产品4 还有23个
    消耗了: 产品5 还有22个
"""

5.线程队列-先进先出队列,后进先出队列,优先级队列

from multiprocessing import Queue  # 是用于多进程的队列,就是专门用来做进程间通信(IPC)
import queue  # 是用于同一进程内的队列,不能做多进程之间的通信

q = queue.Queue()
# 先进先出
q.put(1)
q.put(2)
q.put(3)
print(q.get())
print(q.get())

q = queue.LifoQueue()
# 后进先出的队列
q.put(1)
q.put(2)
q.put(3)
print(q.get())

q = queue.PriorityQueue()
# 优先级队列,put()方法接收的是一个元组(),第一个位置是优先级,第二个位置是数据
# 优先级如果是数字,直接比较数值
# 如果是字符串,是按照 ASCII 码比较的,当ASCII码相同时,会按照先进先出的原则
q.put((1, 'abc'))
q.put((5, 'qwe'))
q.put((-5, 'zxc'))
print(q.get())
print(q.get())

6.信号量-Semaphore

from threading import Semaphore
from threading import Thread
import time

def func(sem, i):
    sem.acquire()
    print('第%s个人进入屋子' % i)
    time.sleep(2)
    print('第%s个人离开屋子' % i)
    sem.release()

sem = Semaphore(5)
for i in range(20):
    t = Thread(target=func, args=(sem, i))
    t.start()