简单了解多线程

并发和并行

并发： 在同一时刻，多个指令在单一CPU上交替指向

并行：在同一时刻，多个指令在多个CPU上同时执行

2核4线程，4核8线程，8核16线程，16核32线程

基础实现线程的方式

• Thread :继承类 ，无返回
• Runnable ：实现接口，无返回
• Callable 核 TaskFurture ： 实现接口，有返回

public static void main(String[] args) {
        
        MyThread t1 = new MyThread();
        t1.setName("自定义线程-1");
        MyThread t2 = new MyThread("自定义线程-2");
        t1.start();
        t2.start();
    }

    static class MyThread extends  Thread{

//        int ticket = 100; // 单个线程私有
//        static int ticket = 100; // MyThread类启动的多线程共有

        public MyThread() {
        }

        public MyThread(String name) {
            super(name);
        }

        @Override
        public void run() {
            for (int i=1;i<1000;i++){
                System.out.println(Thread.currentThread().getName()+"   "+i);
            }
        }
    }

public class RunnableMain {
    public static void main(String[] args) {
        MyRunnable r1 = new MyRunnable();
        Thread t1 = new Thread(r1,"自定义线程-1");
        Thread t2 = new Thread(t1,"自定义线程-2");

        t1.start();
        t2.start();
    }

    static class MyRunnable implements Runnable{
        // int ticket = 100; // 线程共享

        @Override
        public void run() {
            for (int i=1;i<1000;i++){
                System.out.println(Thread.currentThread().getName()+"   "+i);
            }
        }
    }
}

public class CallableMain {
    public static void main(String[] args) throws ExecutionException, InterruptedException {
        MyCallable c1 = new MyCallable();
        FutureTask<Integer> f1 = new FutureTask<>(c1);
        Thread t1 = new Thread(f1);
        t1.start();

        System.out.println(f1.get());
    }

    static class MyCallable implements Callable<Integer>{
        @Override
        public Integer call() throws Exception {
            Integer count = 0;
            for (int i=1;i<1000;i++){
                count+=i;
            }
            return count;
        }
    }
}

常见的成员方法

生命周期

同步代码块synchronized ()，同步方法，local锁

// lock是接口，用ReentrantLock实现
Lock reentrantLock = new ReentrantLock();
reentrantLock.lock();
reentrantLock.unlock();
注意退出的时候，是否带锁退出，最好放在finally块里

死锁：相互等待

等待/唤醒

锁.wait();
锁.notifyAll(); //唤醒所有

这两个方法必须在同步代码块内部调用

交替执行： 

public class MyArrayBlockingQueue {
    static Integer count = 10;
    static Integer hasFood = 0;
    static Object obj = new Object();

    public static void main(String[] args) {
        Cooker cooker = new Cooker();
        Eater eater = new Eater();

        Thread t1 = new Thread(cooker);
        Thread t2 = new Thread(eater);
        t1.start();
        t2.start();
    }

    @Data
    static
    class Cooker implements Runnable {
        private ArrayBlockingQueue abq;

        @Override
        public void run() {
            while (true) {
                if (count == 0) {
                    break;
                } else {
                    synchronized (MyArrayBlockingQueue.obj) {
                        if (hasFood == 1) {
                            // 有食物
                            try {
                                MyArrayBlockingQueue.obj.wait();
                            } catch (InterruptedException e) {
                                e.printStackTrace();
                            }
                        } else {
                            hasFood++;
                            System.out.println("做了一份菜");
                            MyArrayBlockingQueue.obj.notifyAll();
                        }
                    }
                }
            }
        }
    }

    @Data
    static
    class Eater implements Runnable {
        private ArrayBlockingQueue abq;

        @Override
        public void run() {
            while (true) {
                if (count == 0) {
                    break;
                } else {
                    synchronized (MyArrayBlockingQueue.obj) {
                        if (hasFood == 0) {
                            // 没有食物
                            try {
                                MyArrayBlockingQueue.obj.wait();
                            } catch (InterruptedException e) {
                                e.printStackTrace();
                            }
                        } else {
                            hasFood--;
                            count--;
                            System.out.println("吃了一份菜，还剩下" + count + "容量的肚子");
                            MyArrayBlockingQueue.obj.notifyAll();
                        }
                    }
                }
            }
        }
    }

}

阻塞队列

继承：

Iterable -> Collection -> Queue -> BlockingQueue -> ArrayBlockQueue(数组有界) / LinkedBlockQueue（数组无界）

线程池

// 获取一个单线程的线程池：
ExecutorService singleThreadExecutor = Executors.newSingleThreadExecutor();

// 获取FixThread 线程池： 指定活跃线程数量2
ExecutorService executorService = Executors.newFixedThreadPool(2);

// 创建一个可缓存的线程连接池,无限大（完全取决于操作系统最大允许多少）
// 超过60秒自动回收
ExecutorService cachedThreadPool = Executors.newCachedThreadPool();

// 1. 获取周期性线程池, 传入核心线程的大小
ScheduledExecutorService scheduledExecutorService = Executors.newScheduledThreadPool(2);

多线程(二) | 彻底搞懂线程池-Executors_executor.submit-CSDN博客