// 在main方法中，開啟100個線程執(zhí)行 lock() 方法
// 開啟10個線程執(zhí)行 unlock() 方法
// 此時進行加鎖和解鎖之后，加鎖多于解鎖的時候，就會一直阻塞等待
public class Demo01 {
    private boolean isLocked = false;

    public synchronized void lock() throws InterruptedException {
        while (isLocked) {
            // 當其他線程進來，即處于等待阻塞狀態(tài)   
            wait();
        }
        System.out.println("Demo01.lock");
        isLocked = true;
    }

    public synchronized void unlock() {
        isLocked = false;
        System.out.println("Demo01.unlock");
        notify();
    }

    public static void main(String[] args) {
        Demo01 demo01 = new Demo01();
        for (int i = 0; i < 100; i++) {
            new Thread(() -> {
                try {
                    demo01.lock();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }).start();
        }
        for (int i = 0; i < 10; i++) {
            new Thread(() -> {
                demo01.unlock();
            }).start();
        }
    }
}

// 非阻塞鎖
public class Demo02 {
    private boolean isLocked = false;

    public synchronized boolean lock() throws InterruptedException {
        if (isLocked) {
            return false;
        }
        System.out.println("Demo01.lock");
        isLocked = true;
        return true;
    }

    public synchronized boolean unlock() {
        if (isLocked) {
            System.out.println("Demo01.unlock");
            isLocked = !isLocked;
            return true;
        }
        return false;
    }

    public static void main(String[] args) {
        Demo02 demo01 = new Demo02();
        for (int i = 0; i < 100; i++) {
            new Thread(() -> {
                try {
                    if (demo01.lock()) {
                        System.out.println("獲取鎖失敗");
                    }
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }).start();
        }
        for (int i = 0; i < 1000; i++) {
            new Thread(() -> {
                if (demo01.unlock()) {
                    System.out.println("解鎖成功");
                }
            }).start();
        }
    }
}

public class Test implements Runnable {

    public synchronized void get() {
        System.out.println(Thread.currentThread().getId());
        set();
    }

    public synchronized void set() {
        System.out.println(Thread.currentThread().getId());
    }

    @Override
    public void run() {
        get();
    }

    public static void main(String[] args) {
        Test ss = new Test();
        new Thread(ss).start();
        new Thread(ss).start();
        new Thread(ss).start();
    }
}
// 執(zhí)行結(jié)果
// 11
// 11
// 12
// 12
// 13
// 13

public class Test2 implements Runnable {
    ReentrantLock lock = new ReentrantLock();

    public void get() {
        lock.lock();
        try {
            System.out.println(Thread.currentThread().getId());
            set();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            lock.unlock();
        }
    }

    public void set() {
        lock.lock();
        try {
            System.out.println(Thread.currentThread().getId());
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            lock.unlock();
        }
    }

    @Override
    public void run() {
        get();
    }

    public static void main(String[] args) {
        Test ss = new Test();
        new Thread(ss).start();
        new Thread(ss).start();
        new Thread(ss).start();
    }
}
// 執(zhí)行結(jié)果
// 11
// 11
// 12
// 12
// 13
// 13

public class SpinLock {
    private AtomicReference<Thread> owner = new AtomicReference<>();

    public void lock() {
        Thread current = Thread.currentThread();
        while (!owner.compareAndSet(null, current)) {
        }
    }

    public void unlock() {
        Thread current = Thread.currentThread();
        owner.compareAndSet(current, null);
    }

public class SpinLock1 {
    private AtomicReference<Thread> owner =new AtomicReference<>();
    private int count =0;
    public void lock(){
        Thread current = Thread.currentThread();
        if(current==owner.get()) {
            count++;
            return ;
        }
        while(!owner.compareAndSet(null, current)){
        }
    }
    public void unlock (){
        Thread current = Thread.currentThread();
        if(current==owner.get()){
            if(count!=0){
                count--;
            }else{
                owner.compareAndSet(current, null);
            }
        }
    }
}

public class ReentrantReadWriteLock
    implements ReadWriteLock, java.io.Serializable {
    private static final long serialVersionUID = -6992448646407690164L;

    // 讀鎖內(nèi)部類對象
    private final ReentrantReadWriteLock.ReadLock readerLock;

    // 寫鎖內(nèi)部類對象
    private final ReentrantReadWriteLock.WriteLock writerLock;

    // 執(zhí)行所有的同步機制
    final Sync sync;

    // 無參構(gòu)造函數(shù) 調(diào)用有參構(gòu)造 ReentrantReadWriteLock(boolean fair)
    public ReentrantReadWriteLock() {
        this(false);
    }

    // 有參構(gòu)造函數(shù) 是否創(chuàng)建公平鎖
    public ReentrantReadWriteLock(boolean fair) {
        sync = fair ? new FairSync() : new NonfairSync();
        readerLock = new ReadLock(this);
        writerLock = new WriteLock(this);
    }

    //  返回讀鎖和寫鎖的對象
    public ReentrantReadWriteLock.WriteLock writeLock() { return writerLock; }
    public ReentrantReadWriteLock.ReadLock  readLock()  { return readerLock; }

    // 繼承自 AbstractQueueSynchronizer 的Sync
    abstract static class Sync extends AbstractQueuedSynchronizer {
        private static final long serialVersionUID = 6317671515068378041L;

        // 共享移位
        static final int SHARED_SHIFT   = 16;
        // 共享單位
        static final int SHARED_UNIT    = (1 << SHARED_SHIFT);
        // 最大數(shù)量
        static final int MAX_COUNT      = (1 << SHARED_SHIFT) - 1;
        // 獨占
        static final int EXCLUSIVE_MASK = (1 << SHARED_SHIFT) - 1;

        // 返回共享鎖的數(shù)量 
        static int sharedCount(int c)    { return c >>> SHARED_SHIFT; }
        // 返回獨占鎖的數(shù)量
        static int exclusiveCount(int c) { return c & EXCLUSIVE_MASK; }

        // 每線程讀取保持計數(shù)的計數(shù)器
        static final class HoldCounter {
            int count = 0;
            // 使用id 而不是使用引用 避免垃圾殘留
            final long tid = getThreadId(Thread.currentThread());
        }

        // 線程本地子類
        static final class ThreadLocalHoldCounter
            extends ThreadLocal<HoldCounter> {
            public HoldCounter initialValue() {
                return new HoldCounter();
            }
        }

        // 當前線程持有的可重入鎖的數(shù)量，只在構(gòu)造函數(shù)和readObject中初始化，
        // 當線程的讀取保持計數(shù)下降到0的時候刪除
        private transient ThreadLocalHoldCounter readHolds;

        // 獲取readLock的最后一個線程的保持計數(shù)
        private transient HoldCounter cachedHoldCounter;

        // 第一個獲得讀的線程
        private transient Thread firstReader = null;
        // 計數(shù)器
        private transient int firstReaderHoldCount;

        Sync() {
            readHolds = new ThreadLocalHoldCounter();
            setState(getState()); // ensures visibility of readHolds
        }

        // 當前線程獲取鎖的時候由于策略超過其他等待線程而應(yīng)阻止，返回true
        abstract boolean readerShouldBlock();

        // 如果由于試圖超越其他等待線程的策略而導致當前線程在嘗試獲取寫鎖（且有資格這樣做）
        // 時應(yīng)阻塞，則返回true
        abstract boolean writerShouldBlock();

        // 嘗試釋放
        protected final boolean tryRelease(int releases) {
            if (!isHeldExclusively())
                throw new IllegalMonitorStateException();
            int nextc = getState() - releases;
            boolean free = exclusiveCount(nextc) == 0;
            if (free)
                setExclusiveOwnerThread(null);
            setState(nextc);
            return free;
        }

        // 嘗試增加
        protected final boolean tryAcquire(int acquires) {
            /*
             * Walkthrough:
             * 1. If read count nonzero or write count nonzero
             *    and owner is a different thread, fail.
             * 2. If count would saturate, fail. (This can only
             *    happen if count is already nonzero.)
             * 3. Otherwise, this thread is eligible for lock if
             *    it is either a reentrant acquire or
             *    queue policy allows it. If so, update state
             *    and set owner.
             */
            Thread current = Thread.currentThread();
            int c = getState();
            int w = exclusiveCount(c);
            if (c != 0) {
                // (Note: if c != 0 and w == 0 then shared count != 0)
                if (w == 0 || current != getExclusiveOwnerThread())
                    return false;
                if (w + exclusiveCount(acquires) > MAX_COUNT)
                    throw new Error("Maximum lock count exceeded");
                // Reentrant acquire
                setState(c + acquires);
                return true;
            }
            if (writerShouldBlock() ||
                !compareAndSetState(c, c + acquires))
                return false;
            setExclusiveOwnerThread(current);
            return true;
        }

        // 嘗試釋放共享鎖
        protected final boolean tryReleaseShared(int unused) {
            Thread current = Thread.currentThread();
            if (firstReader == current) {
                // assert firstReaderHoldCount > 0;
                if (firstReaderHoldCount == 1)
                    firstReader = null;
                else
                    firstReaderHoldCount--;
            } else {
                HoldCounter rh = cachedHoldCounter;
                if (rh == null || rh.tid != getThreadId(current))
                    rh = readHolds.get();
                int count = rh.count;
                if (count <= 1) {
                    readHolds.remove();
                    if (count <= 0)
                        throw unmatchedUnlockException();
                }
                --rh.count;
            }
            for (;;) {
                int c = getState();
                int nextc = c - SHARED_UNIT;
                if (compareAndSetState(c, nextc))
                    // Releasing the read lock has no effect on readers,
                    // but it may allow waiting writers to proceed if
                    // both read and write locks are now free.
                    return nextc == 0;
            }
        }

        // 非法的監(jiān)視器狀態(tài)異常
        private IllegalMonitorStateException unmatchedUnlockException() {
            return new IllegalMonitorStateException(
                "attempt to unlock read lock, not locked by current thread");
        }

        // 嘗試加共享鎖
        protected final int tryAcquireShared(int unused) {
            /*
             * Walkthrough:
             * 1. If write lock held by another thread, fail.
             * 2. Otherwise, this thread is eligible for
             *    lock wrt state, so ask if it should block
             *    because of queue policy. If not, try
             *    to grant by CASing state and updating count.
             *    Note that step does not check for reentrant
             *    acquires, which is postponed to full version
             *    to avoid having to check hold count in
             *    the more typical non-reentrant case.
             * 3. If step 2 fails either because thread
             *    apparently not eligible or CAS fails or count
             *    saturated, chain to version with full retry loop.
             */
            Thread current = Thread.currentThread();
            int c = getState();
            if (exclusiveCount(c) != 0 &&
                getExclusiveOwnerThread() != current)
                return -1;
            int r = sharedCount(c);
            if (!readerShouldBlock() &&
                r < MAX_COUNT &&
                compareAndSetState(c, c + SHARED_UNIT)) {
                if (r == 0) {
                    firstReader = current;
                    firstReaderHoldCount = 1;
                } else if (firstReader == current) {
                    firstReaderHoldCount++;
                } else {
                    HoldCounter rh = cachedHoldCounter;
                    if (rh == null || rh.tid != getThreadId(current))
                        cachedHoldCounter = rh = readHolds.get();
                    else if (rh.count == 0)
                        readHolds.set(rh);
                    rh.count++;
                }
                return 1;
            }
            return fullTryAcquireShared(current);
        }

        // 讀取的完整版本，可處理CAS丟失和tryAcquireShared中未處理的可重入讀取
        final int fullTryAcquireShared(Thread current) {

            HoldCounter rh = null;
            for (;;) {
                int c = getState();
                if (exclusiveCount(c) != 0) {
                    if (getExclusiveOwnerThread() != current)
                        return -1;

                } else if (readerShouldBlock()) {

                    if (firstReader == current) {
                        // assert firstReaderHoldCount > 0;
                    } else {
                        if (rh == null) {
                            rh = cachedHoldCounter;
                            if (rh == null || rh.tid != getThreadId(current)) {
                                rh = readHolds.get();
                                if (rh.count == 0)
                                    readHolds.remove();
                            }
                        }
                        if (rh.count == 0)
                            return -1;
                    }
                }
                if (sharedCount(c) == MAX_COUNT)
                    throw new Error("Maximum lock count exceeded");
                if (compareAndSetState(c, c + SHARED_UNIT)) {
                    if (sharedCount(c) == 0) {
                        firstReader = current;
                        firstReaderHoldCount = 1;
                    } else if (firstReader == current) {
                        firstReaderHoldCount++;
                    } else {
                        if (rh == null)
                            rh = cachedHoldCounter;
                        if (rh == null || rh.tid != getThreadId(current))
                            rh = readHolds.get();
                        else if (rh.count == 0)
                            readHolds.set(rh);
                        rh.count++;
                        cachedHoldCounter = rh; // cache for release
                    }
                    return 1;
                }
            }
        }

        // 執(zhí)行tryLock進行寫入，從而在兩種模式下都可以進行插入，這與tryAcquire的作用相同
        // 只是缺少對 writerShouldBlock的調(diào)用
        final boolean tryWriteLock() {
            Thread current = Thread.currentThread();
            int c = getState();
            if (c != 0) {
                int w = exclusiveCount(c);
                if (w == 0 || current != getExclusiveOwnerThread())
                    return false;
                if (w == MAX_COUNT)
                    throw new Error("Maximum lock count exceeded");
            }
            if (!compareAndSetState(c, c + 1))
                return false;
            setExclusiveOwnerThread(current);
            return true;
        }

        // 執(zhí)行tryLock進行讀取，從而在兩種模式下都可以進行插入。 
        // 除了沒有調(diào)用readerReaderShouldBlock以外，這與tryAcquireShared的作用相同。
        final boolean tryReadLock() {
            Thread current = Thread.currentThread();
            for (;;) {
                int c = getState();
                if (exclusiveCount(c) != 0 &&
                    getExclusiveOwnerThread() != current)
                    return false;
                int r = sharedCount(c);
                if (r == MAX_COUNT)
                    throw new Error("Maximum lock count exceeded");
                if (compareAndSetState(c, c + SHARED_UNIT)) {
                    if (r == 0) {
                        firstReader = current;
                        firstReaderHoldCount = 1;
                    } else if (firstReader == current) {
                        firstReaderHoldCount++;
                    } else {
                        HoldCounter rh = cachedHoldCounter;
                        if (rh == null || rh.tid != getThreadId(current))
                            cachedHoldCounter = rh = readHolds.get();
                        else if (rh.count == 0)
                            readHolds.set(rh);
                        rh.count++;
                    }
                    return true;
                }
            }
        }

        // 是否獨占鎖
        protected final boolean isHeldExclusively() {
            return getExclusiveOwnerThread() == Thread.currentThread();
        }

        // 返回Condition對象
        final ConditionObject newCondition() {
            return new ConditionObject();
        }

        // 返回獨占鎖
        final Thread getOwner() {
            return ((exclusiveCount(getState()) == 0) ?
                    null :
                    getExclusiveOwnerThread());
        }

        // 獲取readLock所得個數(shù)
        final int getReadLockCount() {
            return sharedCount(getState());
        }

        // 判斷是否是 writeLock 鎖
        final boolean isWriteLocked() {
            return exclusiveCount(getState()) != 0;
        }

        // 獲得寫鎖的數(shù)量
        final int getWriteHoldCount() {
            return isHeldExclusively() ? exclusiveCount(getState()) : 0;
        }

        // 獲得讀鎖的數(shù)量
        final int getReadHoldCount() {
            if (getReadLockCount() == 0)
                return 0;

            Thread current = Thread.currentThread();
            if (firstReader == current)
                return firstReaderHoldCount;

            HoldCounter rh = cachedHoldCounter;
            if (rh != null && rh.tid == getThreadId(current))
                return rh.count;

            int count = readHolds.get().count;
            if (count == 0) readHolds.remove();
            return count;
        }

        // 序列化
        private void readObject(java.io.ObjectInputStream s)
            throws java.io.IOException, ClassNotFoundException {
            s.defaultReadObject();
            readHolds = new ThreadLocalHoldCounter();
            setState(0); // reset to unlocked state
        }

        // 獲取數(shù)量
        final int getCount() { return getState(); }
    }

    // 非公平鎖
    static final class NonfairSync extends Sync {
        private static final long serialVersionUID = -8159625535654395037L;
        final boolean writerShouldBlock() {
            return false; // writers can always barge
        }
        final boolean readerShouldBlock() {
            return apparentlyFirstQueuedIsExclusive();
        }
    }

    // 公平鎖
    static final class FairSync extends Sync {
        private static final long serialVersionUID = -2274990926593161451L;
        final boolean writerShouldBlock() {
            return hasQueuedPredecessors();
        }
        final boolean readerShouldBlock() {
            return hasQueuedPredecessors();
        }
    }

    // 讀鎖實現(xiàn)了 Lock 接口
    public static class ReadLock implements Lock, java.io.Serializable {
        private static final long serialVersionUID = -5992448646407690164L;
        private final Sync sync;

        // 初始化，獲得是否是公平讀鎖
        protected ReadLock(ReentrantReadWriteLock lock) {
            sync = lock.sync;
        }

        // 加鎖 是共享鎖
        public void lock() {
            sync.acquireShared(1);
        }

        // 鎖中斷
        public void lockInterruptibly() throws InterruptedException {
            sync.acquireSharedInterruptibly(1);
        }

        // 調(diào)用加鎖
        public boolean tryLock() {
            return sync.tryReadLock();
        }

        // 超時加鎖
        public boolean tryLock(long timeout, TimeUnit unit)
            throws InterruptedException {
            return sync.tryAcquireSharedNanos(1, unit.toNanos(timeout));
        }

        // 解鎖
        public void unlock() {
            sync.releaseShared(1);
        }

        // Condition 對象
        public Condition newCondition() {
            throw new UnsupportedOperationException();
        }

        // toString方法
        public String toString() {
            int r = sync.getReadLockCount();
            return super.toString() +
                "[Read locks = " + r + "]";
        }
    }

    // 寫鎖
    public static class WriteLock implements Lock, java.io.Serializable {
        private static final long serialVersionUID = -4992448646407690164L;
        private final Sync sync;

        // 寫鎖初始化
        protected WriteLock(ReentrantReadWriteLock lock) {
            sync = lock.sync;
        }

        // 加鎖
        public void lock() {
            sync.acquire(1);
        }

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

        // 加鎖
        public boolean tryLock( ) {
            return sync.tryWriteLock();
        }

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

        // 解鎖，調(diào)用 release 減1
        public void unlock() {
            sync.release(1);
        }

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

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

        // 是否有獨占的線程
        public boolean isHeldByCurrentThread() {
            return sync.isHeldExclusively();
        }

        // 獲取寫鎖的數(shù)量
        public int getHoldCount() {
            return sync.getWriteHoldCount();
        }
    }

    // 判斷是否是公平鎖
    public final boolean isFair() {
        return sync instanceof FairSync;
    }

    // 判斷是否是獨占鎖
    protected Thread getOwner() {
        return sync.getOwner();
    }

    // 獲取讀鎖的個數(shù)
    public int getReadLockCount() {
        return sync.getReadLockCount();
    }

    // 判斷是否是寫鎖
    public boolean isWriteLocked() {
        return sync.isWriteLocked();
    }

    // 判斷鎖是否被當前線程持有
    public boolean isWriteLockedByCurrentThread() {
        return sync.isHeldExclusively();
    }

    // 查詢當前線程對該鎖的可重入寫入次數(shù)
    public int getWriteHoldCount() {
        return sync.getWriteHoldCount();
    }

    // 查詢當前線程對該鎖的可重讀次數(shù)
    public int getReadHoldCount() {
        return sync.getReadHoldCount();
    }

    // 返回寫線程的集合
    protected Collection<Thread> getQueuedWriterThreads() {
        return sync.getExclusiveQueuedThreads();
    }

    // 返回讀線程的集合
    protected Collection<Thread> getQueuedReaderThreads() {
        return sync.getSharedQueuedThreads();
    }

    // 查詢是否有任何線程正在等待獲取讀或?qū)戞i
    public final boolean hasQueuedThreads() {
        return sync.hasQueuedThreads();
    }

    //  查詢指定線程是否在等待讀或者寫鎖
    public final boolean hasQueuedThread(Thread thread) {
        return sync.isQueued(thread);
    }

    // 獲取等待隊列的長度
    public final int getQueueLength() {
        return sync.getQueueLength();
    }

    // 獲得等待隊列中的線程集合
    protected Collection<Thread> getQueuedThreads() {
        return sync.getQueuedThreads();
    }

    // 查詢是否有任何線程正在等待與寫鎖關(guān)聯(lián)的給定條件
    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);
    }

    // 查詢是否有任何線程正在等待與寫鎖關(guān)聯(lián)的給定條件的長度
    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);
    }

    // 獲得給定條件等待線程的集合
    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);
    }

    // toString()方法
    public String toString() {
        int c = sync.getCount();
        int w = Sync.exclusiveCount(c);
        int r = Sync.sharedCount(c);

        return super.toString() +
            "[Write locks = " + w + ", Read locks = " + r + "]";
    }

    // 獲取線程ID
    static final long getThreadId(Thread thread) {
        return UNSAFE.getLongVolatile(thread, TID_OFFSET);
    }

    // Unsafe對象
    private static final sun.misc.Unsafe UNSAFE;
    private static final long TID_OFFSET;
    static {
        try {
            UNSAFE = sun.misc.Unsafe.getUnsafe();
            Class<?> tk = Thread.class;
            TID_OFFSET = UNSAFE.objectFieldOffset
                (tk.getDeclaredField("tid"));
        } catch (Exception e) {
            throw new Error(e);
        }
    }
}

@Override
public synchronized StringBuffer append(String str) {
    toStringCache = null;
    super.append(str);
    return this;
}

public class Demo {
    public static void main(String[] args) {
        long start = System.currentTimeMillis();
        int size = 10000;
        for (int i = 0; i < size; i++) {
            createStringBuffer("ic", "java");
        }
        long timeCost = System.currentTimeMillis() - start;
        System.out.println("createStringBuffer:" + timeCost + " ms");
    }
    public static String createStringBuffer(String str1, String str2) {
        StringBuffer sBuf = new StringBuffer();
        // append方法是同步操作
        sBuf.append(str1);
        sBuf.append(str2);
        return sBuf.toString();
    }
}

public class Semaphore implements java.io.Serializable {
    private static final long serialVersionUID = -3222578661600680210L;

    // Sync鎖
    private final Sync sync;

    // Sync實現(xiàn)了AbstractQueueSynchronizer
    abstract static class Sync extends AbstractQueuedSynchronizer {
        private static final long serialVersionUID = 1192457210091910933L;

        //  初始化版本初始值
        Sync(int permits) {
            setState(permits);
        }

        // 獲取狀態(tài)
        final int getPermits() {
            return getState();
        }

        // 不公平嘗試共享
        final int nonfairTryAcquireShared(int acquires) {
            for (;;) {
                int available = getState();
                int remaining = available - acquires;
                if (remaining < 0 ||
                    compareAndSetState(available, remaining))
                    return remaining;
            }
        }

        // 嘗試釋放共享
        protected final boolean tryReleaseShared(int releases) {
            for (;;) {
                int current = getState();
                int next = current + releases;
                if (next < current) // overflow
                    throw new Error("Maximum permit count exceeded");
                if (compareAndSetState(current, next))
                    return true;
            }
        }

        // 減少狀態(tài)的指定值
        final void reducePermits(int reductions) {
            for (;;) {
                int current = getState();
                int next = current - reductions;
                if (next > current) // underflow
                    throw new Error("Permit count underflow");
                if (compareAndSetState(current, next))
                    return;
            }
        }

        final int drainPermits() {
            for (;;) {
                int current = getState();
                if (current == 0 || compareAndSetState(current, 0))
                    return current;
            }
        }
    }

    // 非公平鎖
    static final class NonfairSync extends Sync {
        private static final long serialVersionUID = -2694183684443567898L;

        NonfairSync(int permits) {
            super(permits);
        }

        protected int tryAcquireShared(int acquires) {
            return nonfairTryAcquireShared(acquires);
        }
    }

    // 公平鎖
    static final class FairSync extends Sync {
        private static final long serialVersionUID = 2014338818796000944L;

        FairSync(int permits) {
            super(permits);
        }

        protected int tryAcquireShared(int acquires) {
            for (;;) {
                if (hasQueuedPredecessors())
                    return -1;
                int available = getState();
                int remaining = available - acquires;
                if (remaining < 0 ||
                    compareAndSetState(available, remaining))
                    return remaining;
            }
        }
    }

    // 構(gòu)造方法 設(shè)置初始版本號
    public Semaphore(int permits) {
        sync = new NonfairSync(permits);
    }

    // 構(gòu)造方法
    public Semaphore(int permits, boolean fair) {
        sync = fair ? new FairSync(permits) : new NonfairSync(permits);
    }

    // 增加1
    public void acquire() throws InterruptedException {
        sync.acquireSharedInterruptibly(1);
    }

    // 不間斷地獲取
    public void acquireUninterruptibly() {
        sync.acquireShared(1);
    }

    // 從此信號量獲取許可，直到獲得一個許可為止，將一直阻塞
    public void acquireUninterruptibly() {
        sync.acquireShared(1);
    }

    // 僅在調(diào)用時可用時，才從此信號量獲取許可
    public boolean tryAcquire() {
        return sync.nonfairTryAcquireShared(1) >= 0;
    }

    // 定時設(shè)置
    public boolean tryAcquire(long timeout, TimeUnit unit)
        throws InterruptedException {
        return sync.tryAcquireSharedNanos(1, unit.toNanos(timeout));
    }

    // 釋放
    public void release() {
        sync.releaseShared(1);
    }

    // 設(shè)置指定的個數(shù)
    public void acquire(int permits) throws InterruptedException {
        if (permits < 0) throw new IllegalArgumentException();
        sync.acquireSharedInterruptibly(permits);
    }

    // 獲得許可證的給定數(shù)目從這個信號，阻塞直到所有可用。
    public void acquireUninterruptibly(int permits) {
        if (permits < 0) throw new IllegalArgumentException();
        sync.acquireShared(permits);
    }

    // 獲得許可證的給定數(shù)目從此信號量，只有在所有可在調(diào)用的時候。
    public boolean tryAcquire(int permits) {
        if (permits < 0) throw new IllegalArgumentException();
        return sync.nonfairTryAcquireShared(permits) >= 0;
    }

    // 收購從此信號量許可證的給定數(shù)量，如果所有給定的等待時間內(nèi)變得可用，并且當前線程未被中斷 
    public boolean tryAcquire(int permits, long timeout, TimeUnit unit)
        throws InterruptedException {
        if (permits < 0) throw new IllegalArgumentException();
        return sync.tryAcquireSharedNanos(permits, unit.toNanos(timeout));
    }

    // 釋放
    public void release(int permits) {
        if (permits < 0) throw new IllegalArgumentException();
        sync.releaseShared(permits);
    }

    // 返回現(xiàn)在的剩余值
    public int availablePermits() {
        return sync.getPermits();
    }

    // 返回減少之后的值
    public int drainPermits() {
        return sync.drainPermits();
    }

    // 減少指定個數(shù)的值
    protected void reducePermits(int reduction) {
        if (reduction < 0) throw new IllegalArgumentException();
        sync.reducePermits(reduction);
    }

    // 判斷是否時公平鎖
    public boolean isFair() {
        return sync instanceof FairSync;
    }

    // 判斷隊列是否有線程 
    public final boolean hasQueuedThreads() {
        return sync.hasQueuedThreads();
    }

    // 返回線程的長度
    public final int getQueueLength() {
        return sync.getQueueLength();
    }

    // 返回隊列線程的集合
    protected Collection<Thread> getQueuedThreads() {
        return sync.getQueuedThreads();
    }

    // toString() 方法
    public String toString() {
        return super.toString() + "[Permits = " + sync.getPermits() + "]";
    }
}

// 它默認是非公平鎖
public ReentrantLock() {
    sync = new NonfairSync();
}

// 創(chuàng)建ReentrantLock，公平鎖or非公平鎖
public ReentrantLock(boolean fair) {
    sync = fair ? new FairSync() : new NonfairSync();
}

// 而他會分別調(diào)用lock方法和unlock方法來釋放鎖
public void lock() {
    sync.lock();
}

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

public class DeadLockDemo {
    public static void main(String[] args) {
        String lockA = "lockA";
        String lockB = "lockB";
        MyThread myThread1 = new MyThread(lockA,lockB);
        MyThread myThread2 = new MyThread(lockB,lockA);
        new Thread(myThread1).start();
        new Thread(myThread2).start();
    }

}

class MyThread implements Runnable {

    private String lockA;
    private String lockB;

    public MyThread(String lockA, String lockB) {
        this.lockA = lockA;
        this.lockB = lockB;
    }

    @Override
    public void run() {
        synchronized (lockA) {
            System.out.println(Thread.currentThread().getName() + "lock：" + lockA + " => " + lockB);
            try {
                TimeUnit.SECONDS.sleep(2);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            synchronized (lockB) {
                System.out.println(Thread.currentThread().getName() + "lock：" + lockB + " => " + lockA);
            }
        }
    }
}