Python多线程中线程间资源共享和常用的锁机制的介绍

from threading import Thread, Lock
lock = Lock()
total = 0

'''如果不使用lock那么，最后得到的数字不一定为0；同时loack不支持连续多次acquire，如果这样做了的后果是死锁！'''
def add():
    global total
    global lock
    for i in range(1000000):
        lock.acquire()
        total += 1
        lock.release()
    
def sub():
    global total
    global lock
    for i in range(1000000):
        lock.acquire()
        total -= 1
        lock.release()
    
thread1 = Thread(target=add)
thread2 = Thread(target=sub)


# 将Thread1和2设置为守护线程，主线程完成时，子线程也一起结束
# thread1.setDaemon(True)
# thread1.setDaemon(True)

# 启动线程
thread1.start()
thread2.start()

# 阻塞，等待线程1和2完成，如果不使用join，那么主线程完成后，子线程也会自动关闭。
thread1.join()
thread2.join()

total

from threading import Thread, Lock
from queue import Queue

def add(q):
    if q.not_full:
        q.put(1)
    
def sub(q):
    if q.not_empty:
        recv = q.get()
        print(recv)
        q.task_done()
        
if __name__ =='__main__':
    # 设置q最多接收3个任务,Queue是线程安全的，所以不需要Lock
    qu = Queue(3)
    thread1 = Thread(target=add, args=(qu,))
    thread2 = Thread(target=sub, args=(qu,))
    thread1.start()
    thread2.start()
    # q队列堵塞，等待所有任务都被处理完。
    qu.join()

from threading import Thread, Lock
lock = Lock()
total = 0

'''如果不使用lock那么，最后得到的数字不一定为0；同时lock不支持连续多次acquire，如果这样做了的后果是死锁！'''
def add():
    global total
    global lock
    for i in range(1000000):
        lock.acquire()
        total += 1
        lock.release()
    
def sub():
    global total
    global lock
    for i in range(1000000):
        lock.acquire()
        total -= 1
        lock.release()
    
thread1 = Thread(target=add)
thread2 = Thread(target=sub)

# 将Thread1和2设置为守护线程，主线程完成时，子线程也一起结束
# thread1.setDaemon(True)
# thread1.setDaemon(True)

# 启动线程
thread1.start()
thread2.start()

# 阻塞，等待线程1和2完成，如果不使用join，那么主线程完成后，子线程也会自动关闭。
thread1.join()
thread2.join()
total

from threading import Thread, Lock, RLock
lock = RLock()
total = 0
def add():
    global lock
    global total
    # RLock实现连续获取锁，但是需要相应数量的release来释放资源
    for i in range(1000000):
        lock.acquire()
        lock.acquire()
        total += 1
        lock.release()
        lock.release()
def sub():
    global lock
    global total
    for i in range(1000000):
        lock.acquire()
        total -= 1
        lock.release()
thread1 = Thread(target=add)
thread2 = Thread(target=sub)
thread1.start()
thread2.start()
thread1.join()
thread2.join()
total

from threading import Thread, Condition
'''聊天
    Peaple1 : How are you?
    Peaple2 : I`m fine, thank you!
    
    Peaple1 : What`s your job?
    Peaple2 : My job is teacher.
    
'''

def Peaple1(condition):
    with condition:
        print('Peaple1 : ', 'How are you?')
        condition.notify()
        condition.wait()
        
        print('Peaple1 : ', 'What`s your job?')
        condition.notify()
        condition.wait()

def Peaple2(condition):
    with condition:
        condition.wait()
        print('Peaple2 : ', 'I`m fine, thank you!')
        condition.notify()
        
        condition.wait()
        print('Peaple2 : ', 'My job is teacher.')
        condition.notify()


if __name__ == '__main__':
    cond = Condition()
    thread1 = Thread(target=Peaple1, args=(cond,))
    thread2 = Thread(target=Peaple2, args=(cond,))
    
    # 此处thread2要比thread1提前启动，因为notify必须要有wait接收；如果先启动thread1,没有wait接收notify信号，那么将会死锁。
    thread2.start()
    thread1.start()

#     thread1.join()
#     thread2.join()

#Semaphore 是用于控制进入数量的锁
#文件， 读、写， 写一般只是用于一个线程写，读可以允许有多个

import threading
import time

class HtmlSpider(threading.Thread):
    def __init__(self, url, sem):
        super().__init__()
        self.url = url
        self.sem = sem

    def run(self):
        time.sleep(2)
        print("Download {html} success\n".format(html=self.url))
        self.sem.release()

class UrlProducer(threading.Thread):
    def __init__(self, sem):
        super().__init__()
        self.sem = sem

    def run(self):
        for i in range(20):
            self.sem.acquire()
            html_thread = HtmlSpider("https://www.baidu.com/{}".format(i), self.sem)
            html_thread.start()

if __name__ == "__main__":
    # 控制锁的数量, 每次同时会有3个线程获得锁，然后输出
    sem = threading.Semaphore(3)
    url_producer = UrlProducer(sem)
    url_producer.start()