[basic 8] - processes and threads

process （Process） It is a description of a running process of a program in a computer . The finished code , When not running , Become a program ; Running code , The running process is called process .
For the operating system , A task is a process （Process）, For example, opening a browser is to start a browser process , Open a notepad and start a notepad process , Opening two notebooks starts two Notepad processes , Open one Word It starts a Word process .
Some processes do more than one thing at a time , such as Word, It can type at the same time 、 Spelling check 、 Printing and so on . Within a process , Do many things at the same time , You need to run multiple “ The subtasks ”, We put these in the process “ The subtasks ” Called thread （Thread）.
Because every process has at least one thing to do , therefore , A process has at least one Threads . Of course , image Word This complex process can have multiple threads , Multiple threads can execute at the same time , Multithreading is the same as multiprocessing , It is also the operating system that switches between multiple threads quickly , Let each thread run alternately for a short time , It looks like it's being executed at the same time . Of course , Really multithreading at the same time requires multiple cores CPU It's possible .
Threads are the smallest unit of execution , And the process is made up of at least one thread . How to schedule processes and threads , It's entirely up to the operating system , The program itself can't decide when to execute , How long does it take .

Implement multitasking in one program , You can use multithreading and multiprocessing

Multi process

Multi process creation ： Use Process class , Every time this class is instantiated , Just create a process object .

Multi process ： During the operation of a program , Multiple processes have been generated
1.n A running program — At least n A process
2.1 Procedures ----- There may be only one process , There may also be multiple processes

# Introduce process class 
from multiprocessing import Process
import time

# Mission 1
def run1():
    print(" Performed the mission 1！")
    time.sleep(5)

# Mission 2
def run2():
    print(" Performed the mission 2！")
    time.sleep(5)

# Mission 3
def run3():
    print(" Performed the mission 3！")
    time.sleep(5)

#------------------------ Serial 
# run1()
# run2()
# run3()

#------------------------ parallel 
# Create process object 
p1=Process(target=run1)  #(target= Task method to be performed )
p2=Process(target=run2)
p3=Process(target=run3)

if __name__=='__main__':
    p1.start()# Start the process , Can only write main in 
    p2.start()
    p3.start()

Start the process , Can only write main in

Performed the mission 1！
Performed the mission 2！
Performed the mission 3！

Multithreading

• Thread is CPU The basic unit of dispatch , It is the specific execution unit in the process ;
• The process contains threads , A process contains at least one thread ;
• If a process contains multiple threads , It's called multithreading .

Implementation of multithreading ：

1. introduce threading modular
2. Creating thread objects
3. Start thread

import threading
import time

def run(name):
    print(" Performed the mission ！")
    time.sleep(5)

#-- Creating thread objects 
t1=threading.Thread(target=run,args=("t1",))
t2=threading.Thread(target=run,args=("t2",))
t3=threading.Thread(target=run,args=("t3",))

# Start thread 
t1.start()
t2.start()
t3.start()

# Multi process switching consumes CPU More resources 

Performed the mission ！
Performed the mission ！
Performed the mission ！

Main thread and child thread

When the program is executed , The program itself is a thread , Called the main thread
Manually created threads , Called a child thread
The main thread will not wait for the sub thread to finish executing , Will directly execute the following code

import threading
import time

def run(name):
    print(" Performed the mission ！")
    time.sleep(5)

#-- Creating thread objects 
t1=threading.Thread(target=run,args=("t1",))
t2=threading.Thread(target=run,args=("t2",))
t3=threading.Thread(target=run,args=("t3",))

# Start thread 
t1.start()
t2.start()
t3.start()

t1.join()# You need to wait for the current thread to finish executing , Can continue to execute the main thread 
t2.join()
t3.join()

print(" completion of enforcement ！")

Performed the mission ！
Performed the mission ！
Performed the mission ！
completion of enforcement ！

join Method enables the current thread to continue executing the main thread after it finishes executing

Thread lock

When a thread sets a lock , Only wait until the lock is released , To schedule other threads

import threading

num=100
def run(name):
    global num
    num-=1
    print(" Threads ",name," Yes , at present num The value of is ：",num)

for i in range(1,101):
    t=threading.Thread(target=run,args=(i,))
    t.start()

If thread lock is not used , The running results may be disordered

Threads 1 Yes , at present num The value of is ： 99
Threads 2 Yes , at present num The value of is ： 98
Threads 3 Yes , at present num The value of is ： 97
Threads 4 Yes , at present num The value of is ： Threads 5 Yes , at present num The value of is ：96
95
Threads 6 Yes , at present num The value of is ： 94
········
Threads 100 Yes , at present num The value of is ： 0

• Use thread lock

import threading

#  Thread lock （ The mutex ）： When a thread sets a lock , Only wait until the lock is released , To schedule other threads 
lock=threading.Lock()# Create a lock 
num=100

def run(name):
    global num
    num-=1
    print(" Threads ",name," Yes , at present num The value of is ：",num)

for i in range(1,101):
    t=threading.Thread(target=run,args=(i,))
    t.start()

There will be no confusion

Case study

Multithreaded chat room

from threading import Thread
from socket import *

# Receiving information 
def recvData():
    msg=s.recv(1024)
    print(">>:",msg.decode())

 # Send a message 
def sendData():
    info=input("<<:")
    s.sendto(info.encode(),(ip,port))

 #--------------------
ip="localhost"# other party ip
port=9001# Opposite port number 

s=socket(AF_INET,SOCK_DGRAM)
s.bind(("localhost",9002))

tr=Thread(target=recvData)
ts=Thread(target=recvData)

tr.start()
ts.start()