public class Mutex implements Sync  {
  /** The lock status **/
  protected boolean inuse_ = false;
  @Override
  public void acquire() throws InterruptedException {
    if (Thread.interrupted()) {
      throw new InterruptedException();
    }
    synchronized(this) {
      try {
        //如果inuse_為true就wait住線程
        while (inuse_) {
          wait();
        }
        inuse_ = true;
      }
      catch (InterruptedException ex) {
        notify();
        throw ex;
      }
    }
  }
  /**
   * 釋放鎖，通知線程繼續(xù)執(zhí)行
   */
  @Override
  public synchronized void release()  {
    inuse_ = false;
    notify(); 
  }
  @Override
  public boolean attempt(long msecs) throws InterruptedException {
    if (Thread.interrupted()) {
      throw new InterruptedException();
    }
    synchronized(this) {
      if (!inuse_) {
        inuse_ = true;
        return true;
      }
      else if (msecs <= 0) {
        return false;
      } else {
        long waitTime = msecs;
        long start = System.currentTimeMillis();
        try {
          for (;;) {
            wait(waitTime);
            if (!inuse_) {
              inuse_ = true;
              return true;
            }
            else {
              waitTime = msecs - (System.currentTimeMillis() - start);
              if (waitTime <= 0) 
                return false;
            }
          }
        }
        catch (InterruptedException ex) {
          notify();
          throw ex;
        }
      }
    }  
  }
}

public class CountDown implements Sync {
    protected final int initialCount_;
    protected int count_;
    /**
     * Create a new CountDown with given count value
     **/
    public CountDown(int count) {
        count_ = initialCount_ = count;
    }
    @Override
    public void acquire() throws InterruptedException {
        if (Thread.interrupted()) {
            throw new InterruptedException();
        }
        synchronized (this) {
            while (count_ > 0) {
                wait();
            }
        }
    }
    @Override
    public boolean attempt(long msecs) throws InterruptedException {
        if (Thread.interrupted()) {
            throw new InterruptedException();
        }
        synchronized (this) {
            if (count_ <= 0) {
                return true;
            } else if (msecs <= 0) {
                return false;
            } else {
                long waitTime = msecs;
                long start = System.currentTimeMillis();
                for (; ; ) {
                    wait(waitTime);
                    if (count_ <= 0) {
                        return true;
                    } else {
                        waitTime = msecs - (System.currentTimeMillis() - start);
                        if (waitTime <= 0) {
                            return false;
                        }
                    }
                }
            }
        }
    }
    /**
     * Decrement the count.
     * After the initialCount'th release, all current and future
     * acquires will pass
     **/
    @Override
    public synchronized void release() {
        if (--count_ == 0) {
            notifyAll();
        }
    }
    /**
     * Return the initial count value
     **/
    public int initialCount() {
        return initialCount_;
    }
    public synchronized int currentCount() {
        return count_;
    }
}

public interface Sync {
  public void acquire() throws InterruptedException;
  public boolean attempt(long msecs) throws InterruptedException;
  public void release();
  /**  One second, in milliseconds; convenient as a time-out value **/
  public static final long ONE_SECOND = 1000;
  /**  One minute, in milliseconds; convenient as a time-out value **/
  public static final long ONE_MINUTE = 60 * ONE_SECOND;
  /**  One hour, in milliseconds; convenient as a time-out value **/
  public static final long ONE_HOUR = 60 * ONE_MINUTE;
  /**  One day, in milliseconds; convenient as a time-out value **/
  public static final long ONE_DAY = 24 * ONE_HOUR;
  /**  One week, in milliseconds; convenient as a time-out value **/
  public static final long ONE_WEEK = 7 * ONE_DAY;
  /**  One year in milliseconds; convenient as a time-out value  **/
  public static final long ONE_YEAR = (long)(365.2425 * ONE_DAY);
  /**  One century in milliseconds; convenient as a time-out value **/
  public static final long ONE_CENTURY = 100 * ONE_YEAR;
}

/**
   用于創(chuàng)建鎖和其他同步類的基本線程阻塞基礎(chǔ)類，提供基礎(chǔ)的線程控制功能。
 */
public class LockSupport {
    private LockSupport() {}
    /**
      解除park的阻塞，如果還沒阻塞，它對{@code park}的下一次調(diào)用將保證不會(huì)阻塞
     */
    public static void unpark(Thread thread) {
        if (thread != null) {
            UNSAFE.unpark(thread);
        }
    }
    /**
      阻塞當(dāng)前線程，除非先調(diào)用了unpark()方法。
     */
    public static void park() {
        UNSAFE.park(false, 0L);
    }
    //Hotspot implementation via intrinsics API
    private static final Unsafe UNSAFE;
    static {
        try {
            try {
                final PrivilegedExceptionActionaction = new PrivilegedExceptionAction() {
                    @Override
                    public Unsafe run() throws Exception {
                        Field theUnsafe = Unsafe.class.getDeclaredField("theUnsafe");
                        theUnsafe.setAccessible(true);
                        return (Unsafe) theUnsafe.get(null);
                    }
                };
                UNSAFE = AccessController.doPrivileged(action);
            } catch (Exception e) {
                throw new RuntimeException("Unable to load unsafe", e);
            }
        } catch (Exception ex) { throw new Error(ex); }
    }
}

/**
 * 簡版先進(jìn)先出的公平鎖實(shí)現(xiàn)
 * @author: kl @kailing.pub
 * @date: 2019/9/2
 */
public class FIFOMutex {
    private final AtomicBoolean locked = new AtomicBoolean(false);
    private final Queuewaiters = new ConcurrentLinkedQueue<>();
    public void lock() {
        boolean wasInterrupted = false;
        Thread current = Thread.currentThread();
        waiters.add(current);
        // 在隊(duì)列中不是第一個(gè)或無法獲取鎖時(shí)阻塞
        while (waiters.peek() != current || !locked.compareAndSet(false, true)) {
            LockSupport.park(this);
            if (Thread.interrupted()) {
                wasInterrupted = true;
            }
        }
        waiters.remove();
        if (wasInterrupted) {
            current.interrupt();
        }
    }
    public void unlock() {
        locked.set(false);
        LockSupport.unpark(waiters.peek());
    }
}

private static final sun.misc.Unsafe UNSAFE = sun.misc.Unsafe.getUnsafe();

private static final Unsafe UNSAFE;
    static {
        try {
            try {
                final PrivilegedExceptionActionaction = new PrivilegedExceptionAction() {
                    @Override
                    public Unsafe run() throws Exception {
                        Field theUnsafe = Unsafe.class.getDeclaredField("theUnsafe");
                        theUnsafe.setAccessible(true);
                        return (Unsafe) theUnsafe.get(null);
                    }
                };
                UNSAFE = AccessController.doPrivileged(action);
            } catch (Exception e) {
                throw new RuntimeException("Unable to load unsafe", e);
            }
        } catch (Exception ex) { throw new Error(ex); }
    }

public native void unpark(Object var1);

public native void park(boolean var1, long var2);

// JSR166 // ------------------------------------------------------- /*
 * The Windows implementation of Park is very straightforward: Basic
 * operations on Win32 Events turn out to have the right semantics to
 * use them directly. We opportunistically resuse the event inherited
 * from Monitor.
 *
void Parker::park(bool isAbsolute, jlong time) {
  guarantee (_ParkEvent != NULL, "invariant") ;
  // First, demultiplex/decode time arguments
  if (time < 0) { // don't wait
    return;
  }
  else if (time == 0 && !isAbsolute) {
    time = INFINITE;
  }
  else if  (isAbsolute) {
    time -= os::javaTimeMillis(); // convert to relative time
    if (time <= 0) // already elapsed
      return;
  }
  else { // relative
    time /= 1000000; // Must coarsen from nanos to millis
    if (time == 0)   // Wait for the minimal time unit if zero
      time = 1;
  }
  JavaThread* thread = (JavaThread*)(Thread::current());
  assert(thread->is_Java_thread(), "Must be JavaThread");
  JavaThread *jt = (JavaThread *)thread;
  // Don't wait if interrupted or already triggered
  if (Thread::is_interrupted(thread, false) ||
    WaitForSingleObject(_ParkEvent, 0) == WAIT_OBJECT_0) {
    ResetEvent(_ParkEvent);
    return;
  }
  else {
    ThreadBlockInVM tbivm(jt);
    OSThreadWaitState osts(thread->osthread(), false /* not Object.wait() */);
    jt->set_suspend_equivalent();
    WaitForSingleObject(_ParkEvent,  time);
    ResetEvent(_ParkEvent); // If externally suspended while waiting, re-suspend if (jt->handle_special_suspend_equivalent_condition()) {
      jt->java_suspend_self();
    }
  }
}
void Parker::unpark() {
  guarantee (_ParkEvent != NULL, "invariant") ;
  SetEvent(_ParkEvent);
}