Java限制可以重入次数的锁

完全 模仿ReentrantLock， 通过继承 java.util.concurrent.locks.Lock , 内置 AbstractQueuedSynchronizer 实现类，限制可以重入次数的锁。

这个其实不难， 只要稍微注意一点就好了

ReenterLimitedLock  关键实现：

/**
 * l.k
 *
 * 限制可以重入次数的锁，默认是2次
 *
 */
public class ReenterLimitedLock implements Lock, java.io.Serializable {
    private static final long serialVersionUID = 7373984872572414699L;
    private final Sync sync;

    /**
     * Creates an instance of {@code ReenterLimitedLock}.
     * This is equivalent to using {@code ReenterLimitedLock(false)}.
     */
    public ReenterLimitedLock() {
        sync = new NonfairSync(2);
    }

    public ReenterLimitedLock(int reenterLimit) {
        sync = new NonfairSync(reenterLimit);
    }

    public ReenterLimitedLock(boolean fair, int reenterLimit) {
        sync = fair ? new FairSync(reenterLimit) : new NonfairSync(reenterLimit);
    }

    public ReenterLimitedLock(boolean fair) {
        sync = fair ? new FairSync(2) : new NonfairSync(2);
    }

    abstract static class Sync extends AbstractQueuedSynchronizer {
        private static final long serialVersionUID = -5179523762034025860L;
        private boolean exceeded;
        private int reenterLimit;

        public Sync(int reenterLimit) {
            this.reenterLimit = reenterLimit;
        }

        abstract void lock();

        final boolean nonfairTryAcquire(int acquires) throws MaximumLockCountExceededException {
            final Thread current = Thread.currentThread();
            int c = getState();
            if (c == 0) {
                if (compareAndSetState(0, acquires)) {
                    setExclusiveOwnerThread(current);
                    return true;
                }
            }
            else if (current == getExclusiveOwnerThread()) {
                int nextc = c + acquires;
//                if (nextc < 0) // overflow
                if (nextc > reenterLimit) { // 关键
                    exceeded = true;
//                    return false;
//                    throw new IllegalStateException("Maximum lock count exceeded" + 2);
                    throw new MaximumLockCountExceededException(reenterLimit);
                }
                setState(nextc);
                return true;
            }
            return false;
        }

        protected final boolean tryRelease(int releases) {
            if (isExceeded()) {
                return false;
            }
            int c = getState() - releases;
            if (Thread.currentThread() != getExclusiveOwnerThread())
                throw new IllegalMonitorStateException();
            boolean free = false;
            if (c == 0) {
                free = true;
                setExclusiveOwnerThread(null);
            }
            setState(c);
            return free;
        }

        protected final boolean isHeldExclusively() {
            // While we must in general read state before owner,
            // we don't need to do so to check if current thread is owner
            return getExclusiveOwnerThread() == Thread.currentThread();
        }

        final ConditionObject newCondition() {
            return new ConditionObject();
        }

        // Methods relayed from outer class

        final Thread getOwner() {
            return getState() == 0 ? null : getExclusiveOwnerThread();
        }

        final int getHoldCount() {
            return isHeldExclusively() ? getState() : 0;
        }

        final boolean isLocked() {
            return getState() != 0;
        }

        /**
         * Reconstitutes the instance from a stream (that is, deserializes it).
         */
        private void readObject(java.io.ObjectInputStream s)
            throws java.io.IOException, ClassNotFoundException {
            s.defaultReadObject();
            setState(0); // reset to unlocked state
        }

        public boolean isExceeded() {
            return exceeded;
        }

        public void setExceeded(boolean exceeded) {
            this.exceeded = exceeded;
        }

        public int getReenterLimit() {
            return reenterLimit;
        }

        public void setReenterLimit(int reenterLimit) {
            this.reenterLimit = reenterLimit;
        }

    }

    /**
     * Sync object for non-fair locks
     */
    static final class NonfairSync extends Sync {
        private static final long serialVersionUID = 7316153563782823691L;

        public NonfairSync(int reenterLimit) {
            super(reenterLimit);
        }

        /**
         * Performs lock.  Try immediate barge, backing up to normal
         * acquire on failure.
         */
        final void lock() {
            if (compareAndSetState(0, 1))
                setExclusiveOwnerThread(Thread.currentThread());
            else
                acquire(1);
        }

        protected final boolean tryAcquire(int acquires) {
            return nonfairTryAcquire(acquires);
        }
    }

    /**
     * Sync object for fair locks
     */
    static final class FairSync extends Sync {
        private static final long serialVersionUID = -3000897897090466540L;

        public FairSync(int reenterLimit) {
            super(reenterLimit);
        }

        final void lock() {
            acquire(1);
        }

        /**
         * Fair version of tryAcquire.  Don't grant access unless
         * recursive call or no waiters or is first.
         */
        protected final boolean tryAcquire(int acquires) {
            final Thread current = Thread.currentThread();
            int c = getState();
            if (c == 0) {
                if (!hasQueuedPredecessors() &&
                    compareAndSetState(0, acquires)) {
                    setExclusiveOwnerThread(current);
                    return true;
                }
            }
            else if (current == getExclusiveOwnerThread()) {
                int nextc = c + acquires;
//                if (nextc < 0)
                if (nextc > getReenterLimit())  //  这里是关键
                    throw new MaximumLockCountExceededException(getReenterLimit());
//                    throw new Error("Maximum lock count exceeded");
                setState(nextc);
                return true;
            }
            return false;
        }
    }

    public void lock() {
        sync.lock();
    }

    public void lockInterruptibly() throws InterruptedException {
        sync.acquireInterruptibly(1);
    }

    public boolean tryLock() {
        return sync.nonfairTryAcquire(1);
    }

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

    public void unlock() {
        sync.release(1);
    }

    public Condition newCondition() {
        return sync.newCondition();
    }

    public int getHoldCount() {
        return sync.getHoldCount();
    }

    public boolean isHeldByCurrentThread() {
        return sync.isHeldExclusively();
    }

    public boolean isLocked() {
        return sync.isLocked();
    }

    public final boolean isFair() {
        return sync instanceof FairSync;
    }

    protected Thread getOwner() {
        return sync.getOwner();
    }

    public final boolean hasQueuedThreads() {
        return sync.hasQueuedThreads();
    }

    public final boolean hasQueuedThread(Thread thread) {
        return sync.isQueued(thread);
    }

    public final int getQueueLength() {
        return sync.getQueueLength();
    }

    protected Collection<Thread> getQueuedThreads() {
        return sync.getQueuedThreads();
    }

    public boolean hasWaiters(Condition condition) {
        if (condition == null)
            throw new NullPointerException();
        if (!(condition instanceof AbstractQueuedSynchronizer.ConditionObject))
            throw new IllegalArgumentException("not owner");
        return sync.hasWaiters((AbstractQueuedSynchronizer.ConditionObject)condition);
    }

    public int getWaitQueueLength(Condition condition) {
        if (condition == null)
            throw new NullPointerException();
        if (!(condition instanceof AbstractQueuedSynchronizer.ConditionObject))
            throw new IllegalArgumentException("not owner");
        return sync.getWaitQueueLength((AbstractQueuedSynchronizer.ConditionObject)condition);
    }

    protected Collection<Thread> getWaitingThreads(Condition condition) {
        if (condition == null)
            throw new NullPointerException();
        if (!(condition instanceof AbstractQueuedSynchronizer.ConditionObject))
            throw new IllegalArgumentException("not owner");
        return sync.getWaitingThreads((AbstractQueuedSynchronizer.ConditionObject)condition);
    }

    public String toString() {
        Thread o = sync.getOwner();
        return super.toString() + ((o == null) ?
                                   "[Unlocked]" :
                                   "[Locked by thread " + o.getName() + "]");
    }
}

MaximumLockCountExceededException 异常：

public class MaximumLockCountExceededException extends IllegalStateException {
//public class MaximumLockCountExceededException extends Exception {
    public MaximumLockCountExceededException(String s) {
        super(s);
    }
    public MaximumLockCountExceededException(int n) {
        super("Maximum lock count exceeded: " + n);
    }
}

测试：

/**
 * Created by L.k on 2018/11/29.
 */
public class Testaa {

    ReenterLimitedLock twiceLock = new ReenterLimitedLock();

    public static void main(String[] args) {
        ReenterLimitedLock twiceLock = new ReenterLimitedLock();
        Testaa testaa =  new Testaa(twiceLock);
        testaa.aa("asf");
    }

    public Testaa(ReenterLimitedLock twiceLock) {
        this.twiceLock = twiceLock;
    }

    public void aa(String aa) {
        try {
            twiceLock.lock();
            Thread.sleep(1000);
            System.out.println("aa = [" + aa + "]");
            bb(aa);
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            twiceLock.unlock();
        }
    }

    public void bb(String bb) {
        try {
            twiceLock.lock();
            Thread.sleep(1000);

            System.out.println("bb = [" + bb + "]");

            cc(bb);

            System.out.println("Testaa.bb");

        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            twiceLock.unlock();
        }
    }

    public void cc(String cc) {
        try {
            twiceLock.lock();
            Thread.sleep(1000);

            System.out.println("cc = [" + cc + "]");

        } catch (InterruptedException e) {
            e.printStackTrace();
//        } catch (InterruptedException | IllegalStateException e) {
        } catch (MaximumLockCountExceededException e) { // 这里必须要 捕获 MaximumLockCountExceededException， 否则 bb 方法也会异常退出
//            e.printStackTrace();
            System.out.println("xxxx IllegalStateException = " + e);
        } finally {
            twiceLock.unlock();
        }
    }
}