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Use of multithreading
2022-06-12 15:18:00 【A_ M amu】
1. Threads
1、 What is thread ？
2. Why do I need threads ？
3. java How to implement multithreading ？
4. java The state of the thread in .
5. Some common methods in threads ？
6. Thread deadlock ？
2. What is thread ？
What is a process ?
1. Running programs . The basic unit of resources allocated by the system . If it's a single core cpu, Macroscopically, processes run in parallel , Microcosmic serial operation .
What is thread ？
Threads , Also known as lightweight process （Light Weight Process）.
An execution path in the process , It's also CPU The basic dispatching unit of .
A process consists of one or more threads , Do different jobs with each other ,
At the same time , It's called multithreading .
3. Why multithreading is needed ？
In order to improve the cpu The usage rate of .
4.java How to implement multithreading ？
java There are three ways to implement multithreading ! 1.5
The first one is : By inheritance Thread class .
The second kind : Realization RUnnable Interface .
The third kind of : Realization Callable Interface .
4.1 Inherit Thead class .
1. Create a thread class and inherit Thread rewrite run Method .
2. stay main Method
3. Start thread start();
package demo01;
/**
* @program: Thread01
* @description:
* @author: Amur
* @create: 2022-01-04 09:05
**/
public class TestThread {
public static void main(String[] args) {
//③ Creating thread objects .
MyThread my=new MyThread();
// ④ Start thread ---- Automatically run Method
my.start();
for (int i = 0; i < 20; i++) { //my Threads main Threads
System.out.println("main======"+i);
}
}
}
//① Create class and inherit Thread class
class MyThread extends Thread{
//② rewrite run Method . The task code executed by the thread
@Override
public void run() {
for (int i = 0; i <20 ; i++) {
System.out.println("myThread========"+i);
}
}
}result :
The results of the analysis :
reflection : Can we control cpu What about the distribution of ?
1. You can't , because java The language cannot manipulate the underlying hardware .
4.2 Get and set the name of the thread
1. Get thread name
1. stay Thread In a subclass of this.getName()
2. Use Thread.currentThread().getName()
2. Set the name of the thread .
1. Through thread objects .setName()
2. By construction method
package demo01;
/**
* @program: Thread01
* @description:
* @author: Amur
* @create: 2022-01-04 09:05
**/
public class TestThread {
public static void main(String[] args) {
//③ Creating thread objects .
MyThread my=new MyThread(" Amur "); // The constructor names the thread
//my.setName(" Threads A"); // call setName() Set the thread name
// ④ Start thread ---- Automatically run Method
my.start();
//③ Creating thread objects .
MyThread my2=new MyThread(" Old wood ");
//my2.setName(" Threads B");
// ④ Start thread ---- Automatically run Method
my2.start();
}
}
//① Create class and inherit Thread class
class MyThread extends Thread{
public MyThread(String name){
super(name);
}
//② rewrite run Method . The task code executed by the thread
@Override
public void run() {
for (int i = 0; i <20 ; i++) {
// Get the name of the current thread this.getName() This class must be Thread Subclasses of .
// If the thread is not named, the default system will follow Thread-n To name 【n:0~】
// System.out.println(this.getName()+"========"+i);
//Thread.currentThread().getName() Can be used anywhere
System.out.println(Thread.currentThread().getName()+"========"+i);
}
}
}4.3 practice
package demo01;
/**
* @program: Thread01
* @description:
* @author: Amur
* @create: 2022-01-04 09:44
**/
public class TestTicket {
public static void main(String[] args) {
Ticket t1=new Ticket(" window A");
Ticket t2=new Ticket(" window B");
Ticket t3=new Ticket(" window C");
Ticket t4=new Ticket(" window D");
t1.start();
t2.start();
t3.start();
t4.start();
}
}
class Ticket extends Thread {
private int ticket = 100;
Ticket(String name){
super(name);
}
@Override
public void run() {
while (true) {
if (ticket <= 0) {
break;
}
ticket--;
System.out.println(Thread.currentThread().getName() + " I bought one , The remaining :" + ticket + " Zhang ");
}
}
}
4.4 Create thread - Realization Runnable Interface .
package demo02;
/**
* @program: Thread01
* @description:
* @author: Amur
* @create: 2022-01-04 09:50
**/
public class TestRunable {
public static void main(String[] args) {
// Create thread task object
MyRunnable my1=new MyRunnable();
// Creating thread objects
Thread t1=new Thread(my1," Threads A"); //public Thread(Runnable target,String name)
t1.start();
// Creating thread objects
Thread t2=new Thread(my1," Threads B"); //public Thread(Runnable target,String name)
t2.start();
}
}
class MyRunnable implements Runnable{
@Override
public void run() { // The task code executed by the thread
for (int i = 0; i <20 ; i++) {
System.out.println(Thread.currentThread().getName()+"~~~~~~~~~~~~"+i);
}
}
}reflection :
1. Which method of thread creation would you choose ?[1] Inherit Thread class 【2】 Realization Runnable.
Choose the second : High expansibility .
4.5 Example
package demo02;
/**
* @program: Thread01
* @description:
* @author: Amur
* @create: 2022-01-04 10:34
**/
public class TestTicket {
public static void main(String[] args) {
Ticket task=new Ticket();// Task object
Thread t1=new Thread(task," window A");
Thread t2=new Thread(task," window B");
Thread t3=new Thread(task," window C");
Thread t4=new Thread(task," window D");
t1.start();
t2.start();
t3.start();
t4.start();
}
}
class Ticket implements Runnable {
private int ticket = 100;
@Override
public void run() {
while (true) {
if (ticket <= 0) {
break;
}
ticket--;
System.out.println(Thread.currentThread().getName() + " Sold one , The remaining :" + ticket + " Zhang ");
}
}
}result :
There are multiple windows selling the same ticket .------- Thread safety problem .
4.6 Example
package demo02;
/**
* @program: Thread01
* @description:
* @author: Amur
* @create: 2022-01-04 10:48
**/
public class TestBank {
public static void main(String[] args) {
// Create a bank card object
BankCard card=new BankCard("123321",0);
// Create a saving task
SaveMoney save=new SaveMoney(card);
// Create a money withdrawal task
TokenMoney token=new TokenMoney(card);
// Create two threads
Thread t1=new Thread(save," Zhang San ");
Thread t2=new Thread(token," Li Si ");
t1.start();
t2.start();
}
}
// Bank cards
class BankCard{
private String no;// Card number
private double balance;// balance
public BankCard(String no, double balance) {
this.no = no;
this.balance = balance;
}
public String getNo() {
return no;
}
public void setNo(String no) {
this.no = no;
}
public double getBalance() {
return balance;
}
public void setBalance(double balance) {
this.balance = balance;
}
}
// Withdraw money
class TokenMoney implements Runnable{
private BankCard bankCard;
public TokenMoney(BankCard bankCard){
this.bankCard=bankCard;
}
@Override
public void run() {
for (int i = 0; i <10 ; i++) {
if(bankCard.getBalance()<1000){
System.out.println(" Insufficient balance in card , Please recharge quickly ........");
i--;
}else{
bankCard.setBalance(bankCard.getBalance()-1000);
System.out.println(Thread.currentThread().getName()+
" The card number is :"+bankCard.getNo()+" Take out 1000, The balance is :"+bankCard.getBalance());
}
}
}
}
// Deposit money
class SaveMoney implements Runnable{
private BankCard bankCard;
public SaveMoney(BankCard bankCard){
this.bankCard=bankCard;
}
@Override
public void run() {
for (int i = 0; i <10 ; i++) {
bankCard.setBalance(bankCard.getBalance()+1000);
System.out.println(Thread.currentThread().getName()+
" The card number is :"+bankCard.getNo()+" Put in 1000, The balance is :"+bankCard.getBalance());
}
}
}summary :
Through this example Each thread can perform different tasks .
5. Common methods in threads .
5.1 sleep
package demo03;
/**
* @program: Thread01
* @description:
* @author: Amur
* @create: 2022-01-04 11:15
**/
public class TestSleep {
public static void main(String[] args) {
My01 my01=new My01();
Thread t1=new Thread(my01," Threads A");
t1.start();
for (int i = 0; i < 20; i++) {
System.out.println("main========="+i);
}
}
}
class My01 implements Runnable{
@Override
public void run() {
for (int i = 0; i <20 ; i++) {
try {
Thread.sleep(200);//0.2 second Simulate network latency
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println(Thread.currentThread().getName()+"===="+i);
}
}
}5.2 yield
public static void yield()
The current thread actively abandons the time slice , Back to ready , Compete for the next time slice
package demo03;
/**
* @program: Thread01
* @description:
* @author: Amur
* @create: 2022-01-04 11:23
**/
public class TestYield {
public static void main(String[] args) {
YieldThread y1=new YieldThread();
YieldThread y2=new YieldThread();
y1.start();
y2.start(); //y1 and y2 The probability of alternate execution is high .
}
}
class YieldThread extends Thread{
@Override
public void run() {
for (int i = 0; i <20 ; i++) {
System.out.println(Thread.currentThread().getName()+"========="+i);
Thread.yield();
}
}
}5.3 join
public final void join()
Allow other threads to join the current thread
package demo03;
/**
* @program: Thread01
* @description:
* @author: Amur
* @create: 2022-01-04 11:29
**/
public class TestJoin {
public static void main(String[] args) throws Exception{
JoinThread t1=new JoinThread();
t1.start();
JoinThread t2=new JoinThread();
t2.start();
t1.join();// Express t1 Thread joins the current main In the thread ,main Threads need to wait t1 The thread will not execute until it has finished executing .
t2.join();
for (int i = 0; i <20 ; i++) {
System.out.println("main=========="+i);
}
}
}
class JoinThread extends Thread{
@Override
public void run() {
for (int i = 0; i <20 ; i++) {
System.out.println(Thread.currentThread().getName()+"============"+i);
}
}
}5. setPriority
package demo03;
/**
* @program: Thread01
* @description:
* @author: Amur
* @create: 2022-01-04 11:34
**/
public class TestPriority {
public static void main(String[] args) {
MyPriority m=new MyPriority();
Thread t1=new Thread(m," Threads A");
Thread t2=new Thread(m," Threads B");
Thread t3=new Thread(m," Threads C");
// t1.setPriority(1);
// t2.setPriority(5);
// t3.setPriority(10); //t3 The highest priority It gets cpu The probability is higher
t1.start();
t2.start();
t3.start();
}
}
class MyPriority implements Runnable{
@Override
public void run() {
for (int i = 0; i <20 ; i++) {
System.out.println(Thread.currentThread().getName()+"========"+i);
}
}
}5.5 setDaemon(true)
The guardian thread :
Thread object .setDaemon(true); Set to daemons .
There are two types of threads : User threads （ Foreground Threads ） And daemons （ Background thread ）
If all foreground threads in the program are executed , The background thread will also end automatically .
The garbage collection thread belongs to the daemon thread .
package demo03;
/**
* @program: Thread01
* @description:
* @author: Amur
* @create: 2022-01-04 11:45
**/
public class TestDeamon {
public static void main(String[] args) {
My m=new My();
My2 m2=new My2();
m.setDaemon(true); // Set up m For the daemons When the main thread ends m The thread will also end
m2.start(); // Foreground Threads
m.start();
for (int i = 0; i <20 ; i++) {
System.out.println(Thread.currentThread().getName()+"======="+i);
}
}
}
class My extends Thread{
@Override
public void run() {
for (int i = 0; i <20 ; i++) {
System.out.println(Thread.currentThread().getName()+"======="+i);
try {
Thread.sleep(2);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
}
class My2 extends Thread{
@Override
public void run() {
for (int i = 0; i <20 ; i++) {
System.out.println(Thread.currentThread().getName()+"======="+i);
}
}
}6, Thread safety problem
package demo04;
import java.util.Arrays;
/**
* @program: Thread01
* @description:
* @author: Amur
* @create: 2022-01-04 11:57
**/
public class TestSafy {
private static String[] arr=new String[5];
private static int index=0;
public static void main(String[] args) throws Exception {
// Create a task to put hello
Runnable tast01=new Runnable() { // Anonymous inner class
@Override
public void run() {
if(arr[index]==null){ // time out
arr[index]="hello";
index++;
}
}
};
Runnable tast02=new Runnable() { // Anonymous inner class
@Override
public void run() {
if(arr[index]==null){
arr[index]="world";// time out
index++;
}
}
};
Thread t1=new Thread(tast01," Threads A");
Thread t2=new Thread(tast02," Threads B");
t1.start();
t2.start();
t1.join();
t2.join();
System.out.println(Arrays.toString(arr)); // Belong to main
}
}
Thread safety problem : How to solve this problem /
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