java 多线程(2)

1.在很多情况下，主线程创建子线程，如果希望主线程等待子线程完成之后再结束，就要用到join()方法了，方法join()的作用是等待线程对象销毁。join()是一个同步方法，需要获得对应线程的锁才能执行，因为它本质是一个wait()，所以join()会释放对应的锁，join(Long)表示最多等待多少毫秒，但是想要继续执行，还是要抢到对应线程的锁。join()源码：

public final void join() throws InterruptedException {
        join(0);//调用下面的方法
    }


public final synchronized void join(long millis)
    throws InterruptedException {
        long base = System.currentTimeMillis();
        long now = 0;

        if (millis < 0) {
            throw new IllegalArgumentException("timeout value is negative");
        }

        if (millis == 0) {
            while (isAlive()) {
                wait(0);
            }
        } else {
            while (isAlive()) {
                long delay = millis - now;
                if (delay <= 0) {
                    break;
                }
                wait(delay);
                now = System.currentTimeMillis() - base;
            }
        }
    }

2.Lock锁 ReentrantLock() https://www.cnblogs.com/Wanted-Tao/p/6378942.html

ReentrantReadWriteLock()锁https://www.cnblogs.com/Wanted-Tao/p/6379363.html

3.lock,condition实现轮流输出A,B,C

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

public class Main {
    private volatile static int key=1;
    private static Lock lock=new ReentrantLock();
    private static Condition conditionA=lock.newCondition();
    private static Condition conditionB=lock.newCondition();
    private static Condition conditionC=lock.newCondition();
    static class ThreadA extends Thread{
        @Override
        public void run() {
            while (true) {
                try {
                    lock.lock();
                    while (key != 1) {
                        conditionA.await();
                    }
                    System.err.println("A");
                    key = 2;
                    conditionB.signal();
                } catch (Exception e) {
                } finally {
                    lock.unlock();
                }
            }
        }
    }
    static class ThreadB extends Thread{
        @Override
        public void run() {
            while (true) {
                try {
                    lock.lock();
                    while (key != 2) {
                        conditionB.await();
                    }
                    System.err.println("B");
                    key = 3;
                    conditionC.signal();
                } catch (Exception e) {
                } finally {
                    lock.unlock();
                }
            }
        }
    }
    static class ThreadC extends Thread{
        @Override
        public void run() {
            while (true) {
                try {
                    lock.lock();
                    while (key != 3) {
                        conditionC.await();
                    }
                    System.err.println("C");
                    key = 1;
                    conditionA.signal();
                } catch (Exception e) {
                } finally {
                    lock.unlock();
                }
            }
        }
    }
    public static void main(String[] args) {
        Thread threadA=new ThreadA();
        Thread threadB=new ThreadB();
        Thread threadC=new ThreadC();
        threadA.start();
        threadB.start();
        threadC.start();


    }
}