GIL全局解释器锁

In CPython, the global interpreter lock, or GIL, is a mutex that prevents multiple 
native threads from executing Python bytecodes at once. This lock is necessary mainly 
because CPython’s memory management is not thread-safe. (However, since the GIL 
exists, other features have grown to depend on the guarantees that it enforces.

import os,time
from multiprocessing import Process
from threading import Thread

‘‘‘
def work():
    res=0
    for i in range(100000000):#做的是计算型的操作
        res*=i

if __name__ == ‘__main__‘:
    l=[]
    print(os.cpu_count())  #8
    start=time.time()
    for i in range(8):#产生8个进程同时执行
        p=Thread(target=work)#run time is 39.95239758491516
        # p=Process(target=work)  #run time is 8.076356410980225
        l.append(p)
        p.start()
    for p in  l:
        p.join()
    stop=time.time()
    print(‘run time is %s‘%(stop-start))
‘‘‘
#io密集型
def work():
    time.sleep(2)

if __name__ == ‘__main__‘:
    start=time.time()
    l=[]
    for i in range(600): #开启600个线程
        p=Process(target=work) #run time is 11.53145694732666
        # p=Thread(target=work)  #run time is 2.06762957572937
        l.append(p)
        p.start()
    for p in l:
        p.join()
    stop=time.time()
    print(‘run time is %s‘%(stop-start))

# from threading import Thread,Lock
# import time
#
# mutex=Lock()
#
#
# n=100
#
# def task():
#
#     global n
#     mutex.acquire()
#     temp=n
#     time.sleep(0.1)
#     n=temp-1
#     mutex.release()
#
# t_list=[]
# for i in range(100):
#     t=Thread(target=task)
#     t.start()
#     t_list.append(t)
#
# for t in t_list:
#     t.join()
#
# print(n)
#     # pass
‘‘‘
对于不同的数据，要想保证安全，必须加不同的锁处理

GIL并不能保证数据的安全，它是对Cpython解释器加锁，针对的是线程

保证的是同一个进程下多个线程之间的安全

‘‘‘
from threading import Thread,Lock

import time

mutex=Lock()
n=100

def task():
    global n
    mutex.acquire()
    temp=n
    time.sleep(0.1)  #模拟网络延迟

    n=temp-1
    mutex.release()

l_list=[]
for i in range(100):
    t=Thread(target=task)
    t.start()
    l_list.append(t)

for t in l_list:
    t.join()

print(n)  #0

#死锁
‘‘‘
import time
from threading import Thread,Lock

mutexA=Lock()
mutexB=Lock()

class MyThead(Thread):
    def run(self):
        self.func1()
        self.func2()


    def func1(self):
        mutexA.acquire()
        print(‘%s 抢到了A锁‘ % self.name)
        mutexB.acquire()
        print(‘%s 抢到了B锁‘ % self.name)
        mutexB.release()
        print(‘%s 释放了B锁‘ % self.name)
        mutexA.release()
        print(‘%s 释放了A锁‘ % self.name)
    def func2(self):
        mutexB.acquire()
        print(‘%s 抢到了B锁‘ % self.name)
        time.sleep(1)
        mutexA.acquire()
        print(‘%s 抢到了A锁‘ % self.name)
        mutexA.release()
        print(‘%s 释放了A锁‘ % self.name)
        mutexB.release()
        print(‘%s 释放了B锁‘ % self.name)


if __name__ == ‘__main__‘:
    for i in range(10):
        t=MyThead()
        t.start()

‘‘‘
#递归锁(解决产生死锁现象)  引用计数0  同一个人（每引用一次，计数+1），下面的人必须等到第一个人释放锁才可以抢
# from threading import Thread,RLock

# mutesA=mutexB=RLock()  #抢锁之后会有一个计数，抢一次计数加1
import time
from threading import Thread,RLock

mutexA=mutexB=RLock()


class MyThead(Thread):
    def run(self):
        self.func1()
        self.func2()


    def func1(self):
        mutexA.acquire()
        print(‘%s 抢到了A锁‘ % self.name)
        mutexB.acquire()
        print(‘%s 抢到了B锁‘ % self.name)
        mutexB.release()
        print(‘%s 释放了B锁‘ % self.name)
        mutexA.release()
        print(‘%s 释放了A锁‘ % self.name)
    def func2(self):
        mutexB.acquire()
        print(‘%s 抢到了B锁‘ % self.name)
        time.sleep(1)
        mutexA.acquire()
        print(‘%s 抢到了A锁‘ % self.name)
        mutexA.release()
        print(‘%s 释放了A锁‘ % self.name)
        mutexB.release()
        print(‘%s 释放了B锁‘ % self.name)


if __name__ == ‘__main__‘:
    for i in range(10):
        t=MyThead()
        t.start()


‘‘‘
自定义锁：一次acquire对应一次release，
递归锁：一次acquire可以不一定要对应release，每产生一次acquire，第一个抢到锁的人的引用计数就+1，除非第一个人释放，否则别人就不会抢到锁
递归锁是解决自定义锁出现的死锁现象
‘‘‘

#钥匙串  公共厕所

from threading import Thread,Semaphore
import time,random

sm=Semaphore(5)   #五个厕所五把锁

def task(name):
    sm.acquire()
    print(‘%s 正在蹲坑‘%name)

    #模拟蹲坑耗时
    time.sleep(random.randint(1,5))
    sm.release()

if __name__ == ‘__main__‘:
    for i in range(20):
        t=Thread(target=task,args=(‘伞兵%s 号‘%i,))
        t.start()

from threading import Event,Thread

import time

event=Event()


def light():
    print(‘红灯亮着！‘)
    time.sleep(3)
    event.set()  #解除阻塞，给我的event发了一个信号
    print(‘绿灯亮着‘)


def car(i):
    print(‘%s 正在等红灯了‘%i)
    event.wait()  #阻塞
    print(‘%s 加油飙车‘%i)

t1=Thread(target=light)
t1.start()

for i in range(10):
    t=Thread(target=car,args=(i,))
    t.start()

import queue

#普通q
# q=queue.Queue(3)
# q.put(1)
# q.put(2)
# q.put(3)
# print(q.get())
# print(q.get())
# print(q.get())
# print(q.get())


#先进后出q
# q=queue.LifoQueue(5)
# q.put(1)
# q.put(2)
# q.put(3)
# q.put(4)
# print(q.get())

#优先级q
q=queue.PriorityQueue()
q.put((10,‘a‘))
q.put((1,‘b‘))
q.put((1,‘c‘))
q.put((1,‘a‘))
q.put((4,‘a‘))
print(q.get())