基于aqs,自定义lock对象

桃扇骨 2022-01-05 13:25 250阅读 0赞

package com.code.constructor.lock;
    
    import java.util.concurrent.TimeUnit;
    import java.util.concurrent.locks.AbstractQueuedSynchronizer;
    import java.util.concurrent.locks.Condition;
    import java.util.concurrent.locks.Lock;
    
    /**
     * 基于aqs实现自定义锁
     */
    public class MyLock1 implements Lock {
    
        private Sync sync = new Sync();
    
        private class Sync extends AbstractQueuedSynchronizer{
    
            /**
             * asq是基于state维护原子性的一致性的.
             * 若当前有锁, 则将其他线程存入队列中.
             */
    
            @Override
            protected boolean tryAcquire(int arg) {
                int state = getState();
                if (state == 0) {
                    if (compareAndSetState(0, arg)) { // 保证了操作的原子性
                        setExclusiveOwnerThread(Thread.currentThread());
                        return true;
                    }
                } else if (Thread.currentThread() == getExclusiveOwnerThread()) { // 重入锁
                    setState(state + 1);
                    return true;
                }
                return false;
            }
    
            @Override
            protected boolean tryRelease(int arg) {
                // 锁的获取与释放肯定是一一对应的
                if (Thread.currentThread() != getExclusiveOwnerThread()) {
                    throw new RuntimeException("运行时异常");
                }
                int state = getState() - arg;
                boolean flag = false;
                if (state == 0) {
                    if (compareAndSetState(getState(), state)) {
                        flag = true;
                        setExclusiveOwnerThread(null);
                    }
                }
                return flag;
            }
    
            public Condition newCondition() {
                return new ConditionObject();
            }
        }
    
        @Override
        public void lock() {
            sync.tryAcquire(1);
        }
    
        @Override
        public void lockInterruptibly() throws InterruptedException {
            sync.acquireInterruptibly(1);
        }
    
        @Override
        public boolean tryLock() {
            return sync.tryAcquire(1);
        }
    
        @Override
        public boolean tryLock(long time, TimeUnit unit) throws InterruptedException {
            return sync.tryAcquireNanos(1, unit.toNanos(time));
        }
    
        @Override
        public void unlock() {
            sync.tryRelease(1);
        }
    
        @Override
        public Condition newCondition() {
            return sync.newCondition();
        }
    }