GIL全局解释器锁
基本概念
- global interpreter lock 全局解释器锁
- GIL不是Python的特性, 是Cpython解释器的特性
- GIL本质是一个互斥锁
- 原因: Cpython解释器的内存管理不是线程安全的
- 作用: 保证同一时间一个进程内只有一个线程在执行
多线程的作用
- 计算密集型---多进程, GIL原因, 一个进程内的线程只能并发, 不能并行
- I/O密集型---多线程, 开启线程与切换线程的速度要快于进程
# 计算密集型
import time
import os
from multiprocessing import Process
from threading import Thread
# 计算密集型
def task1():
number = 0
for i in range(100000000):
number += 1
print('done!')
if __name__ == '__main__':
start_time = time.time()
lis = []
for i in range(4):
# p = Process(target=task1) # 程序执行时间为16.711955785751343
t = Thread(target=task1) # 程序执行时间为26.467514038085938
lis.append(t)
t.start()
for t in lis:
t.join()
end_time = time.time()
print(f'程序执行时间为{end_time - start_time}')
# I/O密集型
import time
import os
from multiprocessing import Process
from threading import Thread
# I/O密集型
def task2():
time.sleep(1)
if __name__ == '__main__':
start_time = time.time()
lis = []
for i in range(20):
# p = Process(target=task2) # 程序执行时间为5.277301788330078
t = Thread(target=task2) # 程序执行时间为1.0040574073791504
lis.append(t)
t.start()
for t in lis:
t.join()
end_time = time.time()
print(f'程序执行时间为{end_time - start_time}')
死锁现象
- 两个或者两个以上的线程在执行过程中, 因为争夺资源而产生的相互等待的状况
from threading import Thread, Lock
import time
mutex_a = Lock()
mutex_b = Lock()
class MyThread(Thread):
def run(self):
self.func1()
self.func2()
def func1(self):
mutex_a.acquire()
print(f'{self.name}拿到了锁a')
mutex_b.acquire()
print(f'{self.name}拿到了锁b')
mutex_b.release()
print(f'{self.name}释放了锁b')
mutex_a.release()
print(f'{self.name}释放了锁a')
def func2(self):
mutex_b.acquire()
print(f'{self.name}拿到了锁b')
# I/O操作
time.sleep(1)
mutex_a.acquire()
print(f'{self.name}拿到了锁a')
mutex_a.release()
print(f'{self.name}释放了锁a')
mutex_b.release()
print(f'{self.name}释放了锁b')
if __name__ == '__main__':
for i in range(4):
t = MyThread()
t.start()
'''
Thread-1拿到了锁a
Thread-1拿到了锁b
Thread-1释放了锁b
Thread-1释放了锁a
Thread-1拿到了锁b
Thread-2拿到了锁a
'''
递归锁
- RLock 内部维护一个Lock和一个计数的counter, counter记录了acquire次数, 使得资源可以被多次请求
- 直到一个线程所有的acquire都被release, 其他线程才能获取资源
from threading import Thread, RLock
import time
mutex_a = mutex_b = RLock()
class MyThread(Thread):
def run(self):
self.func1()
self.func2()
def func1(self):
mutex_a.acquire()
print(f'{self.name}拿到了锁a')
mutex_b.acquire()
print(f'{self.name}拿到了锁b')
mutex_b.release()
print(f'{self.name}释放了锁b')
mutex_a.release()
print(f'{self.name}释放了锁a')
def func2(self):
mutex_b.acquire()
print(f'{self.name}拿到了锁b')
# I/O操作
time.sleep(3)
mutex_a.acquire()
print(f'{self.name}拿到了锁a')
mutex_a.release()
print(f'{self.name}释放了锁a')
mutex_b.release()
print(f'{self.name}释放了锁b')
if __name__ == '__main__':
for i in range(4):
t = MyThread()
t.start()
'''
Thread-1拿到了锁a
Thread-1拿到了锁b
Thread-1释放了锁b
Thread-1释放了锁a
Thread-1拿到了锁b
---间隔了3秒---
Thread-1拿到了锁a
Thread-1释放了锁a
Thread-1释放了锁b
Thread-2拿到了锁a
Thread-2拿到了锁b
Thread-2释放了锁b
Thread-2释放了锁a
Thread-2拿到了锁b
---间隔了3秒---
Thread-2拿到了锁a
Thread-2释放了锁a
Thread-2释放了锁b
Thread-4拿到了锁a
Thread-4拿到了锁b
Thread-4释放了锁b
Thread-4释放了锁a
Thread-4拿到了锁b
---间隔了3秒---
Thread-4拿到了锁a
Thread-4释放了锁a
Thread-4释放了锁b
Thread-3拿到了锁a
Thread-3拿到了锁b
Thread-3释放了锁b
Thread-3释放了锁a
Thread-3拿到了锁b
Thread-3拿到了锁a
Thread-3释放了锁a
Thread-3释放了锁b
'''
信号量
from threading import Semaphore- 相当于多个互斥锁, 可以控制多个线程来访问数据 (可以控制访问资源的线程数量)
sm = Semaphore(5) 表示一次允许5个线程访问数据- acquire 一次, 括号内数字减一, release一次加一, 为0时限制其他线程访问
from threading import Thread, Semaphore, current_thread
import time
# 一次允许5个线程访问数据
sm = Semaphore(5)
def task():
sm.acquire()
print(f'{current_thread().name}已运行...')
time.sleep(3)
sm.release()
if __name__ == '__main__':
for i in range(20):
t = Thread(target=task)
t.start()
'''
Thread-1已运行...
Thread-2已运行...
Thread-3已运行...
Thread-4已运行...
Thread-5已运行...
---间隔了3秒---
Thread-6已运行...
Thread-7已运行...
Thread-8已运行...
Thread-9已运行...
Thread-10已运行...
--间隔了3秒---
Thread-11已运行...
Thread-12已运行...
Thread-13已运行...
Thread-14已运行...
Thread-15已运行...
---间隔3秒---
Thread-17已运行...
Thread-16已运行...
Thread-18已运行...
Thread-19已运行...
Thread-20已运行...
'''
线程队列
queue.Queue() FIFO 先进先出queque.LifoQueue() LIFO 后进先出queque.PriorityQueue() 优先级, 根据元祖内的数据排序
import queue
# 先进先出 FIFO
q1 = queue.Queue()
q1.put(1)
q1.put(2)
q1.put(3)
print(q1.get()) # 1
# 后进先出 LIFO
q2 = queue.LifoQueue()
q2.put(1)
q2.put(2)
q2.put(3)
print(q2.get()) # 3
# 优先级 按元祖内的数据排序
q3 = queue.PriorityQueue()
q3.put(('a',))
q3.put(('b',))
q3.put(('c',))
print(q3.get()) # ('a',)