Multithreading

Table of Contents

Create Thread with Thread Class

public class MyThread extends Thread{
    MyThread(int ID){this.ID = ID;}
    public void run(){
        for (int i = 0; i<100; i++) System.out.println(ID + "\t" + i);
    }
    private int ID;
}

public class Main {
    public static void main(String[] args) {
        MyThread[] threads = new MyThread[4];
        for (int i = 0; i<4; i++) threads[i] = new MyThread(i);
        for (MyThread t : threads) t.start();
    }
}

Create Thread with Runnable Interface

public class MyThread implements Runnable{
    MyThread(int ID){this.ID = ID;}
    public void run(){
        for (int i = 0; i<100; i++) System.out.println(ID + "\t" + i);
    }
    private int ID;
}

public class Main {
    public static void main(String[] args) {
        Thread[] threads = new Thread[4];
        for (int i = 0; i<4; i++) threads[i] = new Thread(new MyThread(i));
        for (Thread t : threads) t.start();

        // Or in other words 
        MyThread MY = new MyThread(6);
        Thread example = new Thread(MY);
        example.start();
    }
}

Thread States

Thread priority

class ThreadDemo extends Thread {
    public void run(){
        System.out.println("Inside run method");
    }
    public static void print_priorities(ThreadDemo[] threads){
        for (int i = 0; i<threads.length; i++)
            System.out.println(threads[i].getPriority());
        System.out.println();
    }
    public static void set_priorities(ThreadDemo[] threads,int[] priorities){
        for (int i = 0; i<threads.length; i++)
            threads[i].setPriority(priorities[i]);
    }

    public static void main(String[] args){
        ThreadDemo[] threads = new ThreadDemo[3];
        for (int i = 0; i<3; i++) threads[i] = new ThreadDemo();
        print_priorities(threads);

        set_priorities(threads,new int[]{2,5,8});
        print_priorities(threads);

        //for main thread
        System.out.println(Thread.currentThread().getName());
        System.out.println(Thread.currentThread().getPriority());
    }
}

Thread Class

.setDaemon(true); Marks this thread as either a daemon thread or a user thread.
.yield(); A hint to the scheduler that the current thread is willing to yield its current use of a processor.

https://docs.oracle.com/javase%2F7%2Fdocs%2Fapi%2F%2F/java/lang/Thread.html

What is a deamon thread

A daemon thread is a thread that does not prevent the JVM from exiting when the program finishes but the thread is still running. An example for a daemon thread is the garbage collection.

You can use the setDaemon(boolean) method to change the Thread daemon properties before the thread starts.

https://stackoverflow.com/questions/2213340/what-is-a-daemon-thread-in-java

Semaphore

https://preshing.com/20150316/semaphores-are-surprisingly-versatile/

Synchronize

class ThreadDemo extends Thread {
    public void run(){
        increment(100_000);
    }
    public static synchronized void increment(int count){
        for (int i = 0; i<count; i++) myint++;
        
    }
    static int myint=0;

    public static void main(String[] args){
        ThreadDemo t1 = new ThreadDemo();
        ThreadDemo t2 = new ThreadDemo();

        t1.start();
        t2.start();
        try{
            t1.join();
            t2.join();
        } catch (InterruptedException e) {
            throw new RuntimeException(e);
        }
        
        System.out.println(myint); // 200000

    }
}

https://stackoverflow.com/questions/2120248/how-to-synchronize-a-static-variable-among-threads-running-different-instances-o