如何实现自定义同步组件

Posted 2020-09-20

package com.chen;

import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.AbstractQueuedSynchronizer;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;

/**
 * desc：自定义同步组件，只允许最多n个线程同时访问
 * // 1.共享访问
 * // 2.定义n个资源数
 * Created by chenjianye on 2017/5/26.
 */
public class ServerLock implements Lock{

    private Sync sync = null;

    public ServerLock(int ServerLockNum) {
        this.sync = new Sync(ServerLockNum);
    }

    private final class Sync extends AbstractQueuedSynchronizer {

        Sync(int count){
            setState(count);
        }

        public int tryAcquireShared(int reduceCount) {
            for(;;) {
                int current = getState();
                int newCount = current - reduceCount;
                if (newCount < 0 || compareAndSetState(current, newCount)) {
                    return newCount;
                }
            }
        }

        public boolean tryReleaseShared(int returnCount) {
            for(;;) {
                int current = getState();
                int newCount = current + returnCount;
                if (compareAndSetState(current, newCount)) {
                    return true;
                }
            }
        }

    }

    @Override
    public void lock() {
//        sync.acquire(1);
        sync.acquireShared(1);
    }

    @Override
    public void unlock() {
        sync.releaseShared(1);
    }

    @Override
    public void lockInterruptibly() throws InterruptedException {
        System.out.println("dd");
    }

    @Override
    public boolean tryLock() {
        return false;
    }

    @Override
    public boolean tryLock(long time, TimeUnit unit) throws InterruptedException {
        return sync.tryAcquireNanos(1, unit.toNanos(1000));
    }

    @Override
    public Condition newCondition() {
        throw new RuntimeException("");
    }

}

package com.chen;

import java.util.concurrent.locks.Lock;

/**
 * desc：测试自定义锁
 * Created by chenjianye on 2017/5/26.
 */
public class TestLock {

    public static void main(String[] args) {
        ServerLock lock = new ServerLock(4);
//        ReentrantReadWriteLock lock = new ReentrantReadWriteLock();
//        Lock tmp = lock.writeLock();
        for(int i=0;i<20;i++) {
            Worker worker = new Worker(lock);
            worker.start();
        }
    }

    static class Worker extends Thread{

        Lock lock;

        Worker(Lock lock) {
            this.lock = lock;
        }

        public void run() {
            while (true) {
                lock.lock();
                try{
                    Thread.sleep(1000);
                    System.out.println("Thread name:" + Thread.currentThread().getName()+"时间："+System.currentTimeMillis()/1000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                } finally {
                    lock.unlock();
                }
            }
        }
    }
}