Java多线程案例之定时器详解

Timer timer = new Timer();
timer.schedule(new TimerTask() {
@Override
public void run() {
System.out.println("hello");
}
}, 3000);

public class Test {
    public static void main(String[] args){
        Timer timer = new Timer();
        timer.schedule(new TimerTask() {
            @Override
            public void run() {
                System.out.println("执行线程在5s后执行");
            }
        },5000);
        timer.schedule(new TimerTask() {
            @Override
            public void run() {
                System.out.println("执行线程在2s后执行");
            }
        },2000);
        timer.schedule(new TimerTask() {
            @Override
            public void run() {
                System.out.println("执行线程在3s后执行");
            }
        },3000);
    }
}

class MyTask implements Comparable<MyTask>{
    //执行的时间戳
    private long time;
    //接受具体任务
    private Runnable runnable;
    //创建MyTask构造方法
    public MyTask(Runnable runnable,long time) {
        //通过currentTimeMillis来获取time 中存的是绝对时间, 超过这个时间的任务就应该被执行
        this.time = System.currentTimeMillis()+time;
        this.runnable = runnable;
    }
    //执行任务
    public void run(){
        this.runnable.run();
    }
    //提供对外time
    public long getTime() {
        return time;
    }
    //执行comparable接口来进行时间的比较,并将time的long类型转换为int类型
    @Override
    public int compareTo(MyTask o) {
        return (int)(this.time-o.time);
    }
}

class MyTimer{
    // 定时器内部要能够存放多个任务
    private PriorityBlockingQueue<MyTask> queue = new PriorityBlockingQueue<>();
    //为锁创建一个对象
    Object locker = new Object();
    public void schedule(Runnable runnable, long delay) {
        MyTask task = new MyTask(runnable, delay);
        queue.put(task);
        // 每次任务插入成功之后, 都唤醒一下扫描线程, 让线程重新检查一下队首的任务看是否时间到要执行~~
        synchronized (locker) {
            locker.notify();
        }
    }

class MyTimer{
    // 定时器内部要能够存放多个任务
    private PriorityBlockingQueue<MyTask> queue = new PriorityBlockingQueue<>();
    //为锁创建一个对象
    Object locker = new Object();
    public void schedule(Runnable runnable, long delay) {
        MyTask task = new MyTask(runnable, delay);
        queue.put(task);
        // 每次任务插入成功之后, 都唤醒一下扫描线程, 让线程重新检查一下队首的任务看是否时间到要执行~~
        synchronized (locker) {
            locker.notify();
        }
    }
    public MyTimer() {
        Thread t = new Thread(() -> {
            while (true) {
                try {
                    // 先取出队首元素
                    MyTask task = queue.take();
                    // 再比较一下看看当前这个任务时间到了没?
                    long curTime = System.currentTimeMillis();
                    if (curTime < task.getTime()) {
                        // 时间没到, 把任务再塞回到队列中.
                        queue.put(task);
                        // 指定一个等待时间,防止有的线程需要等待时间很长，但是线程一直运行等待时间到来执行，这样会占有CPU占有资源
                        synchronized (locker) {
                            locker.wait(task.getTime() - curTime);
                        }
                    } else {
                        // 时间到了, 执行这个任务
                        task.run();
                    }
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        });
        t.start();
    }
}

package thread;

import java.util.PriorityQueue;
import java.util.concurrent.PriorityBlockingQueue;

// 创建一个类, 表示一个任务.
class MyTask implements Comparable<MyTask> {
    // 任务具体要干啥
    private Runnable runnable;
    // 任务具体啥时候干. 保存任务要执行的毫秒级时间戳
    private long time;

    // after 是一个时间间隔. 不是绝对的时间戳的值
    public MyTask(Runnable runnable, long delay) {
        this.runnable = runnable;
        this.time = System.currentTimeMillis() + delay;
    }

    public void run() {
        runnable.run();
    }

    public long getTime() {
        return time;
    }

    @Override
    public int compareTo(MyTask o) {
        // 到底是谁见谁, 才是一个时间小的在前? 需要咱们背下来.
        return (int) (this.time - o.time);
    }
}

class MyTimer {
    // 定时器内部要能够存放多个任务
    private PriorityBlockingQueue<MyTask> queue = new PriorityBlockingQueue<>();

    public void schedule(Runnable runnable, long delay) {
        MyTask task = new MyTask(runnable, delay);
        queue.put(task);
        // 每次任务插入成功之后, 都唤醒一下扫描线程, 让线程重新检查一下队首的任务看是否时间到要执行~~
        synchronized (locker) {
            locker.notify();
        }
    }

    private Object locker = new Object();

    public MyTimer() {
        Thread t = new Thread(() -> {
            while (true) {
                try {
                    // 先取出队首元素
                    MyTask task = queue.take();
                    // 再比较一下看看当前这个任务时间到了没?
                    long curTime = System.currentTimeMillis();
                    if (curTime < task.getTime()) {
                        // 时间没到, 把任务再塞回到队列中.
                        queue.put(task);
                        // 指定一个等待时间
                        synchronized (locker) {
                            locker.wait(task.getTime() - curTime);
                        }
                    } else {
                        // 时间到了, 执行这个任务
                        task.run();
                    }
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        });
        t.start();
    }
}

public class Test {
    public static void main(String[] args) {
        MyTimer myTimer = new MyTimer();
        myTimer.schedule(new Runnable() {
            @Override
            public void run() {
                System.out.println("hello timer!");
            }
        }, 3000);
        System.out.println("main");
    }
}