Parallel and parallel processing in various languages (Java edition)

Let's do the same thing in Java as last time.

long.java

public class Main {

    private static final int REPEAT = 500000000;

    private static long a = 0;

    public static void main(String[] args) throws InterruptedException{

        Thread th1 = new Thread(new Runnable() {
            @Override
            public void run() {
                for(int i = 0;i <REPEAT; i++){
                    a = 1;
                    check();
                }
            }
        });

        Thread th2 = new Thread(new Runnable() {
            @Override
            public void run() {
                for(int i = 0;i <REPEAT; i++){
                    a = -1;
                    check();
                }
            }
        });

        th1.start();
        th2.start();

        th1.join();
        th2.join();

        System.out.println("FINISHED!");
    }

    private static void check(){
        if(a != 1 && a != -1){
            System.out.println("LONG VALUE HAS BROKEN!");
        }
    }
}

Not exclusive control, but there is a volatile modifier to solve a similar problem in Java private volatile static long a = 0; Then the problem disappears.

volatile has the property of "always looking at the latest value when referencing a value". Roughly speaking, volatile assignments and references behave as if they were locked.

But this is not safe, so I use Atomic Long. Atomic: Atomic operation. It means that when performing an operation, others cannot interrupt the operation. private static AtomicLong a = new AtomicLong(0)

Quote: http://d.hatena.ne.jp/cero-t/20120830/1346267076

A synchronized block can be used for exclusive control in Java.

synchronized

public class Main {

    private static final int REPEAT = 500000000;

    private static Long a = new Long(0);

    public static void main(String[] args) throws InterruptedException{

        Thread th1 = new Thread(new Runnable() {
            @Override
            public void run() {
                for(int i = 0;i <REPEAT; i++){
                    synchronized (a){
                        a = new Long(1);
                        check();
                    }
                }
            }
        });

        Thread th2 = new Thread(new Runnable() {
            @Override
            public void run() {
                for(int i = 0;i <REPEAT; i++){
                    synchronized (a) {
                        a = new Long(-1);
                        check();
                    }
                }
            }
        });

        th1.start();
        th2.start();

        th1.join();
        th2.join();

        System.out.println("FINISHED!");
    }

    private static void check(){
        if(a != 1 && a != -1){
            System.out.println("LONG VALUE HAS BROKEN!");
        }
    }
}

Stream # parallel can be used for parallel processing in Java.

parallel

public class Main {

    public static void main(String[] args) {
	// write your code here
        IntStream.range(1,10).parallel().forEach(System.out::println);
    }
}