线程同步的几种方法，join()，CountDownLatchCyclicBarrier Semaphore

Posted 2020-11-26 shihx

package com.example.demo.utils;

import java.lang.reflect.Field;
import java.util.concurrent.*;

public class Test1 {

    static ThreadLocal threadLocal = new ThreadLocal();
    private static CountDownLatch countDownLatch = new CountDownLatch(2);
    static int a = 5;
    static int b = 1;
    
    public Test1() {
    }

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

       Thread t2 = new Thread();

       t1.join();

       t2.join();

    }

    static void f3() {
        ExecutorService executorService = Executors.newFixedThreadPool(4);
        for (int i = 0; i < 4; i++) {
            executorService.submit(() -> {
                int a1 = a--;
                try {
                    Thread.sleep(a * 1000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                System.out.println("thread" + (a1) + " : " + threadLocal.get());
                threadLocal.set(b++);
                System.out.println("thread" + (a1) + ": " + threadLocal.get());
            });
        }
        executorService.shutdown();
    }

    void f2() {
        //回环屏障，可以重复使用
        CyclicBarrier cyclicBarrier = new CyclicBarrier(7);
        //信号量
        Semaphore semaphore = new Semaphore(0);
        ExecutorService executorService = Executors.newFixedThreadPool(6);
        for (int i = 0; i < 6; i++) {
            executorService.submit(() -> {
                try {
                    semaphore.release();
                    Thread.sleep(2000);
                    System.out.println("step1");

                    Thread.sleep(2000);
                    System.out.println("---step2---");
                    semaphore.release();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            });
        }
        try {
            semaphore.acquire();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("over");
//        semaphore.acquire();
//        System.out.println("over9");
        executorService.shutdown();
    }

    void f() {
        ExecutorService executorService = Executors.newFixedThreadPool(2);
        executorService.submit(() -> {
            try {
                Thread.sleep(1000);
                System.out.println("child threadone over");
            } catch (InterruptedException e) {
                e.printStackTrace();
            } finally {
                countDownLatch.countDown();
            }
        });

        executorService.submit(() -> {
            try {
                Thread.sleep(1000);
                System.out.println("child threadtwo over");
            } catch (InterruptedException e) {
                e.printStackTrace();
            } finally {
                countDownLatch.countDown();//递减为0时，阻塞线程恢复
            }
        });
        System.out.println("wait all");
        try {
            countDownLatch.await();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("all is over");
        executorService.shutdown();
    }

}