Required knowledge
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The computer is also called the computer, that is, the brain with electricity. The computer was invented to enable him to work like a human after being powered on, and it is more efficient than human because it can be uninterrupted 24 hours
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The five major components of a computer
Controller
Operator
Memory
input device
Output device
The core of the computer really works is the CPU (controller + arithmetic unit = central processing unit)
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For a program to be run by a computer, its code must be read from the hard disk to memory, and then the CPU fetches instructions before executing
Operating system history
Just refer to the blog: https://www.cnblogs.com/Dominic-Ji/articles/10929381.html
- Punch card
- Online batch processing system
- Offline batch processing system
Multi-channel technology
Single core achieves concurrent effect
Required knowledge
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Concurrency
It looks like running concurrently can be called concurrent
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parallel
Real simultaneous execution
ps:
- Parallel must be considered concurrent
- Single-core computers certainly cannot achieve parallelism, but they can achieve concurrency! ! !
Supplement: We directly assume that a single core is a core, and only one person works, don't consider the number of cores in the CPU
Multi-channel technical illustration
Save the total time spent running multiple programs
Multi-channel technology key knowledge
Taking in space and taking in time
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Spatial multiplexing
Multiple programs share a set of computer hardware
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Multiplexing in time
Example: Washing clothes for 30s, cooking for 50s, boiling water for 30s
Single channel needs 110s, multiple channels only need the long switch of task to save time
Example: Playing a game while eating and saving state
Switch + save state
"""
切换(CPU)分为两种情况
1.当一个程序遇到IO操作的时候，操作系统会剥夺该程序的CPU执行权限
作用:提高了CPU的利用率 并且也不影响程序的执行效率
2.当一个程序长时间占用CPU的时候，操作吸引也会剥夺该程序的CPU执行权限
弊端:降低了程序的执行效率(原本时间+切换时间)
"""
Process theory
Required knowledge
The difference between program and process
"""
程序就是一堆躺在硬盘上的代码，是“死”的
进程则表示程序正在执行的过程，是“活”的
"""
Process scheduling
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First come first served scheduling algorithm
"""对长作业有利，对短作业无益""" -
Short job priority scheduling algorithm
"""对短作业有利，多长作业无益""" -
Time slice rotation method + multi-level feedback queue
Three state diagram of process running
Two pairs of important concepts
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Synchronous and asynchronous
"""描述的是任务的提交方式""" 同步:任务提交之后，原地等待任务的返回结果，等待的过程中不做任何事(干等) 程序层面上表现出来的感觉就是卡住了 异步:任务提交之后，不原地等待任务的返回结果，直接去做其他事情 我提交的任务结果如何获取？ 任务的返回结果会有一个异步回调机制自动处理 -
Blocking non-blocking
"""描述的程序的运行状态""" 阻塞:阻塞态 非阻塞:就绪态、运行态 理想状态:我们应该让我们的写的代码永远处于就绪态和运行态之间切换
Combination of the above concepts: the most efficient combination is asynchronous non-blocking
Two ways to start the process
Dingxinwan: The way code starts processes and threads is basically the same as code writing. You learn how to start processes and you start threads
from multiprocessing import Process
import time
def task(name):
print('%s is running'%name)
time.sleep(3)
print('%s is over'%name)
if __name__ == '__main__':
# 1 创建一个对象
p = Process(target=task, args=('jason',))
# 容器类型哪怕里面只有1个元素 建议要用逗号隔开
# 2 开启进程
p.start() # 告诉操作系统帮你创建一个进程 异步
print('主')
# 第二种方式 类的继承
from multiprocessing import Process
import time
class MyProcess(Process):
def run(self):
print('hello bf girl')
time.sleep(1)
print('get out!')
if __name__ == '__main__':
p = MyProcess()
p.start()
print('主')
to sum up
"""
创建进程就是在内存中申请一块内存空间将需要运行的代码丢进去
一个进程对应在内存中就是一块独立的内存空间
多个进程对应在内存中就是多块独立的内存空间
进程与进程之间数据默认情况下是无法直接交互,如果想交互可以借助于第三方工具、模块
"""
join method
Join is to let the main process wait for the sub-process code to finish running before continuing. Does not affect the execution of other child processes
from multiprocessing import Process
import time
def task(name, n):
print('%s is running'%name)
time.sleep(n)
print('%s is over'%name)
if __name__ == '__main__':
# p1 = Process(target=task, args=('jason', 1))
# p2 = Process(target=task, args=('egon', 2))
# p3 = Process(target=task, args=('tank', 3))
# start_time = time.time()
# p1.start()
# p2.start()
# p3.start() # 仅仅是告诉操作系统要创建进程
# # time.sleep(50000000000000000000)
# # p.join() # 主进程等待子进程p运行结束之后再继续往后执行
# p1.join()
# p2.join()
# p3.join()
start_time = time.time()
p_list = []
for i in range(1, 4):
p = Process(target=task, args=('子进程%s'%i, i))
p.start()
p_list.append(p)
for p in p_list:
p.join()
print('主', time.time() - start_time)
Data isolation between processes
from multiprocessing import Process
money = 100
def task():
global money # 局部修改全局
money = 666
print('子',money)
if __name__ == '__main__':
p = Process(target=task)
p.start()
p.join()
print(money)