1. Principle and mechanism

Use one-way pool to ensure orderly submission and execution.

explain:

1) Alternate execution between threads is not supported.

2) Multithreading is not synchronous, only to ensure the order of execution, multithreading is concurrent execution.

2. Code examples

package com.thread;

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

public class TasksWithoutLockTest extends Thread {

    private static int num = 0;
    private int id;

    public TasksWithoutLockTest(int id) {
        this.id = id;
    }


    @Override
    public void run() {
        System.out.println("Thread" + id + "output num:" + num++);
        try {
            Thread.sleep(3);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    public static void main(String[] args) {
        //ExecutorService exec = Executors.newFixedThreadPool(1);
        ExecutorService exec = Executors.newSingleThreadScheduledExecutor();
        for (int i = 0; i < 12; i++) {
            exec.submit(new TasksWithoutLockTest(i));
        }

        exec.shutdown();

    }
}

3. Output results