五种Java多线程轮询方式

代码可以直接拿去运行的哦!

测试主程序:

/**
 * 线程轮询的五种方法
 * @author chenbin78
 * @version 1.0
 * @create_date 2021/4/19 10:03
 */
public class ThreadPolling {


    public static void main(String[] args) {

        //SynchronizedTest synchronizedTest = new SynchronizedTest();
        //SynchronizedBlock synchronizedBlock = new SynchronizedBlock();
        //ReentrantLockCondition reentrantLockCondition = new ReentrantLockCondition();
        //UnsafeCasTest unsafeCasTest = new UnsafeCasTest();
        AtomicIntegerTest atomicIntegerTest = new AtomicIntegerTest();

        //put线程
        new Thread("put") {
            @Override
            public void run() {
                atomicIntegerTest.put();
            }
        }.start();

        //get线程
        new Thread("get") {
            @Override
            public void run() {
                atomicIntegerTest.get();
            }
        }.start();
    }
}

方法一: 使用synchronized修饰函数:

/**
 * 使用synchronized实现线程的轮询
 * @author chenbin78
 * @version 1.0
 * @create_date 2021/4/19 10:06
 */
public class SynchronizedTest {

    Map<Integer, Integer> map = new HashMap<>();

    private int count = 1;

    synchronized void put() {
        for (int i = 0; i < 10; i++) {
            map.put(count, count);
            System.out.println(Thread.currentThread().getName() + " " + count);
            count ++ ;
            //唤醒get线程
            this.notify(); //等待队列中只有一个线程,所以不使用notfiyAll()
            try {
                //等待get线程取值之后执行
                this.wait();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        System.out.println(Thread.currentThread().getName() + "执行完毕!");
    }

    synchronized void get() {
        for (int i = 0; i < 10; i++) {
            Integer integer = map.get(count - 1);
            System.out.println(Thread.currentThread().getName() + "取值为:" + integer);
            //唤醒put线程
            this.notify(); //等待队列中只有一个线程,所以不使用notfiyAll()
            try {
                //等待put线程赋值之后执行
                //最多等待1s, 等待1s后没被唤醒则自己醒过来
                //因为最后一次循环时, 当前方法让出CPU后, 再也不会被唤醒了
                this.wait(1000);
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
        System.out.println(Thread.currentThread().getName() + "执行完毕");
    }

}

方法二: 使用synchronized代码块:

/**
 * 使用synchronized代码块
 * @author chenbin78
 * @version 1.0
 * @create_date 2021/4/19 10:26
 */
public class SynchronizedBlock {

    private Map<Integer, Integer> map = new HashMap<>();

    private Integer count = 1;


    public void put() {
        synchronized (this) {
            for (int i = 0; i < 10; i++) {
                map.put(count, count);
                System.out.println(Thread.currentThread().getName() + " put:" + count);
                count ++ ;
                this.notify();
                try {
                    this.wait();
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
            System.out.println(Thread.currentThread().getName() + "执行完毕!");
        }
    }

    public void get() {
        synchronized (this) {
            for (int i = 0; i < 10; i++) {
                Integer integer = map.get(count - 1);
                System.out.println(Thread.currentThread().getName() + " get:" + integer);
                this.notify();
                try {
                    this.wait(1000);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        }
        System.out.println(Thread.currentThread().getName() + "执行完毕!");
    }
}

方法三: 使用jdk自带 ReentrantLock锁 + Condition(精准唤醒); 因为 synchronized 能实现的功能ReentrantLock也能实现:

/**
 * 使用ReentrantLock+Condition来实现
 * @author chenbin78
 * @version 1.0
 * @create_date 2021/4/19 10:35
 */
public class ReentrantLockCondition {

    private Map<Integer, Integer> map = new HashMap<>();

    private Integer count = 1;

    ReentrantLock lock = new ReentrantLock();
    Condition condition = lock.newCondition();

    public void put() {
        for (int i = 0; i < 10; i++) {
            try {
                //加锁
                lock.lock();
                map.put(count, count);
                System.out.println(Thread.currentThread().getName() + " put:" + count);
                count ++ ;
                condition.signal();
                try {
                    //让出锁, 但是state应该不变, state应该由lock控制, 并不是condition来控制
                    condition.await();
                } catch (Exception e) {
                    e.printStackTrace();
                }
            } finally {
                //释放锁
                lock.unlock();
            }
        }
    }

    public void get() {
        for (int i = 0; i < 10; i++) {
            try {
                lock.lock();
                Integer integer = map.get(count - 1);
                System.out.println(Thread.currentThread().getName() + " get:" + integer);
                condition.signal();
                try {
                    condition.await(1000, TimeUnit.MILLISECONDS);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            } finally {
                lock.unlock();
            }
        }
    }
}

方法四: 使用Unsafe(安全类)类的CAS操作, 不能操作时便自旋; 不涉及线程的阻塞与唤醒, 更高效:

/**
 * @author chenbin78
 * @version 1.0
 * @create_date 2021/4/19 10:46
 */
public class UnsafeCasTest {

    private Map<Integer, Integer> map = new HashMap<>();

    private Integer count = 1;

    //使用volatile保证flag在两个线程中的可见性
    volatile int flag = 0;

    private static Unsafe unsafe;
    private static Long flagOffset;

    static {
        try {
            unsafe = getUnsafeInstance();
            //获取flag的偏移量, 为CAS操作做准备
            //getDeclaredField()与getField
            flagOffset = unsafe.objectFieldOffset(UnsafeCasTest.class.getDeclaredField("flag"));
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    //获取unsafe实例
    public static Unsafe getUnsafeInstance() throws Exception {
        // 通过反射获取rt.jar下的Unsafe类
        Field theUnsafeInstance = Unsafe.class.getDeclaredField("theUnsafe");
        theUnsafeInstance.setAccessible(true);
        // return (Unsafe) theUnsafeInstance.get(null);是等价的
        return (Unsafe) theUnsafeInstance.get(Unsafe.class);
    }

    public void put() {
        for (int i = 0; i < 10; i++) {
            for (;;) {
                if (flag == 0) {
                    break;
                }
            }
            map.put(count, count);
            System.out.println(Thread.currentThread().getName() + " put:" + count);
            count ++ ;
            int tmp = flag;
            //使用CAS赋值
            unsafe.compareAndSwapInt(this, flagOffset, tmp, 1);
        }
        System.out.println(Thread.currentThread().getName() + "执行完毕!");
    }

    public void get() {
        for (int i = 0; i < 10; i++) {
            for (;;) {
                if (flag == 1) {
                    break;
                }
            }
            Integer integer = map.get(count - 1);
            System.out.println(Thread.currentThread().getName() + " get:" + integer);
            int tmp = flag;
            unsafe.compareAndSwapInt(this, flagOffset, tmp, 0);
        }
        System.out.println(Thread.currentThread().getName() + "执行完毕!");
    }
}

方法五: 使用AtomicInteger(原子操作); 不能操作时便自旋:

/**
 * @author chenbin78
 * @version 1.0
 * @create_date 2021/4/19 11:12
 */
public class AtomicIntegerTest {


    private Map<Integer, Integer> map = new HashMap<>();

    private int count = 1;

    //0表示线程0可以执行, 1表示线程1可以执行
    AtomicInteger atomicInteger = new AtomicInteger(0);

    public void put() {
        for (int i = 0; i < 10; i++) {
            //自旋
            for (;;) {
                if ((atomicInteger.intValue() & 1) == 0) {
                    break;
                }
            }
            map.put(count, count);
            System.out.println(Thread.currentThread().getName() + "put:" + count);
            count ++ ;
            atomicInteger.compareAndSet(atomicInteger.intValue(), 1);
        }
        System.out.println(Thread.currentThread().getName() + "执行完毕!");
    }

    public void get() {
        for (int i = 0; i < 10; i++) {
            //自旋
            for (;;) {
                if ((atomicInteger.intValue() & 1) == 1) {
                    break;
                }
            }
            Integer integer = map.get(count - 1);
            System.out.println(Thread.currentThread().getName() + " get:" + integer);
            atomicInteger.compareAndSet(atomicInteger.intValue(), 0);
        }
        System.out.println(Thread.currentThread().getName() + "执行完毕!");
    }
}

    原文作者:嗯嗯怪666
    原文地址: https://blog.csdn.net/bin0503/article/details/115872002
    本文转自网络文章,转载此文章仅为分享知识,如有侵权,请联系博主进行删除。
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