Based on "immutable class" to implement a thread-safe Integer counter

EDITORIAL

As we all know, java.lang.Stringlike no forced synchronization code, but it is thread-safe, because it is an immutable class, its operations are returned each time a new Stringobject. Rational use of immutable objects can achieve lock-freeresults.

Immutable objects most central places that do not give the opportunity to modify the external shared resources , so as to avoid data inconsistencies multiple threads because the competition for shared resources cause, but also lock-freeavoids the performance loss caused by locks.

ImmutableIntegerCounter

// final 修饰，不能继承
public final class ImmutableIntegerCounter {

    // final 修饰，不允许其他线程对其更改
    private final int initial;

    public ImmutableIntegerCounter(int initial) {
        this.initial = initial;
    }

    public ImmutableIntegerCounter(ImmutableIntegerCounter counter, int i) {
        this.initial = counter.getInitial() + i;
    }

    // 每次调用 increment 都会新构造一个 ImmutableIntegerCounter
    public ImmutableIntegerCounter increment(int i) {
        return new ImmutableIntegerCounter(this, i);
    }

    public int getInitial() {
        return initial;
    }
}

test

import org.junit.Before;
import org.junit.Test;

import java.util.concurrent.TimeUnit;
import java.util.stream.IntStream;

public class ImmutableIntegerCounterTest {

    private ImmutableIntegerCounter integerCounter = null;

    @Before
    public void init() {
        integerCounter = new ImmutableIntegerCounter(0);
    }

    @Test
    public void incrementTest() throws InterruptedException {

        IntStream.range(0, 3).forEach(i -> new Thread(() -> {
            int increment = 1;
            while(true) {
                int oldValue = integerCounter.getInitial();
                int result = integerCounter.increment(increment).getInitial();
                System.out.println(oldValue + "+" + increment + "=" + result);
                assert (oldValue + increment) == result;
                increment++;
                try {
                    TimeUnit.SECONDS.sleep(1);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }).start());

        TimeUnit.SECONDS.sleep(10);

    }
}

Output

The output of the three threads are correct

0+1=1
0+1=1
0+1=1
0+2=2
0+2=2
0+2=2
0+3=3
0+3=3
0+3=3
0+4=4
0+4=4
0+4=4

Process finished with exit code 130 (interrupted by signal 2: SIGINT)