while (!canProceed()) { ... LockSupport.park(this); }

 class FIFOMutex {
 ? private final AtomicBoolean locked = new AtomicBoolean(false);
 ? private final Queue<Thread> waiters
 ? ? = new ConcurrentLinkedQueue<Thread>();
 ? public void lock() {
 ? ? boolean wasInterrupted = false;
 ? ? Thread current = Thread.currentThread();
 ? ? waiters.add(current);
 ? ? // Block while not first in queue or cannot acquire lock
 ? ? while (waiters.peek() != current ||
 ? ? ? ? ? ?!locked.compareAndSet(false, true)) {
 ? ? ? LockSupport.park(this);
 ? ? ? if (Thread.interrupted()) // ignore interrupts while waiting
 ? ? ? ? wasInterrupted = true;
 ? ? }
 ? ? waiters.remove();
 ? ? if (wasInterrupted) ? ? ? ? ?// reassert interrupt status on exit
 ? ? ? current.interrupt();
 ? }
 ? public void unlock() {
 ? ? locked.set(false);
 ? ? LockSupport.unpark(waiters.peek());
 ? }
 }

public class LockSupport {
 ? ?private LockSupport() {} // 無法實例化
 ? ?// ...
}

public class LockSupport {
    // 通過內(nèi)部 API 實現(xiàn) Hotspot
 ? ?private static final Unsafe U = Unsafe.getUnsafe();
 ? ?private static final long PARKBLOCKER= U.objectFieldOffset(Thread.class, "parkBlocker");
 ? ?private static final long TID = U.objectFieldOffset(Thread.class, "tid");
    // ...
}

public class LockSupport {
    public static void unpark(Thread thread)
    public static void park(Object blocker)
    public static void parkNanos(Object blocker, long nanos)
    public static void parkUntil(Object blocker, long deadline)
    public static Object getBlocker(Thread t)
 ? ?public static void setCurrentBlocker(Object blocker)
 ? ?private static void setBlocker(Thread t, Object arg)
    public static void park()
    public static void parkNanos(long nanos)
    public static void parkUntil(long deadline)
 ? ?static final long getThreadId(Thread thread)
}

public static Object getBlocker(Thread t) {
 ? ?if (t == null)
 ? ? ? ?throw new NullPointerException();
 ? ?return U.getReferenceOpaque(t, PARKBLOCKER);
}

private static void setBlocker(Thread t, Object arg) {
 ? ?U.putReferenceOpaque(t, PARKBLOCKER, arg);
}
// 在 JDK 14 之前是不存在該方法的， setBlocker 只能從內(nèi)部進行
public static void setCurrentBlocker(Object blocker) {
 ? ?U.putReferenceOpaque(Thread.currentThread(), PARKBLOCKER, blocker);
}

 setCurrentBlocker(b);
 park(); 
 setCurrentBlocker(null);

@IntrinsicCandidate
public final void putReferenceOpaque(Object o, long offset, Object x) {
 ? ?putReferenceVolatile(o, offset, x);
}
// 使用 volatile 存儲語義將引用值存儲到給定的 Java 變量中。 否則等同于 putReference(Object, long, Object)
@IntrinsicCandidate
public native void putReferenceVolatile(Object o, long offset, Object x);

@IntrinsicCandidate
public final Object getReferenceOpaque(Object o, long offset) {
 ? ?return getReferenceVolatile(o, offset);
}
// 從給定的 Java 變量中獲取引用值，具有可變加載語義。 否則等同于 getReference(Object, long)
@IntrinsicCandidate
public native Object getReferenceVolatile(Object o, long offset);

case vmIntrinsics::_putReferenceVolatile: return inline_unsafe_access( is_store, T_OBJECT, ? Volatile, false);

@IntrinsicCandidate
public native void putReference(Object o, long offset, Object x);

public static void unpark(Thread thread) {
    if (thread != null)
        U.unpark(thread);
}

class LockSupportDemo {
 ? ?fun check() {
 ? ? ? ?val thread1 = Thread {
 ? ? ? ? ? ?Thread.sleep(1000)
 ? ? ? ? ? ?println("thread1 start + ${Date(System.currentTimeMillis())}")
 ? ? ? ? ? ?LockSupport.park()
 ? ? ? ? ? ?println("thread1 end +  ${Date(System.currentTimeMillis())}")
 ? ? ?  }
?
 ? ? ? ?val thread2 = Thread {
 ? ? ? ? ? ?println("thread2 start +  ${Date(System.currentTimeMillis())}")
 ? ? ? ? ? ?LockSupport.unpark(thread1)
 ? ? ? ? ? ?println("thread2 end +  ${Date(System.currentTimeMillis())}")
 ? ? ?  }
 ? ? ? ?thread1.start()
 ? ? ? ?thread2.start()
 ?  }
}

public native void unpark(Object thread);
復制代碼

// 不帶 blocker
public static void park()
public static void parkNanos(long nanos)
public static void parkUntil(long deadline)
// 需要 blocker 參數(shù)
public static void park(Object blocker)
public static void parkNanos(Object blocker, long nanos)
public static void parkUntil(Object blocker, long deadline)

U.park(boolean, long);
復制代碼

public static void park() {
    U.park(false, 0L);
}
public static void parkNanos(long nanos) {
 ? ?if (nanos > 0)
 ? ? ? ?U.park(false, nanos);
}
public static void parkUntil(long deadline) {
 ? ?U.park(true, deadline);
}

public static void park(Object blocker) {
 ? ?Thread t = Thread.currentThread();
 ? ?setBlocker(t, blocker);
 ? ?U.park(false, 0L);
 ? ?setBlocker(t, null);
}
public static void parkNanos(Object blocker, long nanos) {
 ? ?if (nanos > 0) {
 ? ? ? ?Thread t = Thread.currentThread();
 ? ? ? ?setBlocker(t, blocker);
 ? ? ? ?U.park(false, nanos);
 ? ? ? ?setBlocker(t, null);
 ?  }
}
public static void parkUntil(Object blocker, long deadline) {
 ? ?Thread t = Thread.currentThread();
 ? ?setBlocker(t, blocker);
 ? ?U.park(true, deadline);
 ? ?setBlocker(t, null);
}

public class LockSupportJava {
 ? ?Object obj = new Object();?
 ? ?public static void main(String[] args) {
 ? ? ? ?LockSupportJava lock = new LockSupportJava();
 ? ? ? ?lock.waitAndNotify();
 ?  }
 ? ?void waitAndNotify() {
 ? ? ? ?Thread thread1 = new Thread(() -> {
 ? ? ? ? ? ?synchronized(obj) {
 ? ? ? ? ? ? ? ?try {
 ? ? ? ? ? ? ? ?    System.out.println("thread1 start + " + new Date(System.currentTimeMillis()));
 ? ? ? ? ? ? ? ? ? ?Thread.sleep(1000);
 ? ? ? ? ? ? ? ? ? ?obj.notify();
 ? ? ? ? ? ? ?      System.out.println("thread1 end + " + new Date(System.currentTimeMillis()));
 ? ? ? ? ? ? ?  } catch (InterruptedException e) {
 ? ? ? ? ? ? ? ? ? ?e.printStackTrace();
 ? ? ? ? ? ? ?  }
 ? ? ? ? ?  }
 ? ? ?  });?
 ? ? ? ?Thread thread2 = new Thread(() -> {
 ? ? ? ? ? ?synchronized(obj) {
 ? ? ? ? ? ? ? ?try {
 ? ? ? ? ? ? ? ? ? ?thread1.start();
 ? ? ? ? ? ? ? ? ? ?Thread.sleep(3000);
 ? ? ? ? ? ? ? ? ? ?System.out.println("thread2 start + " + new Date(System.currentTimeMillis()));
 ? ? ? ? ? ? ? ? ? ?obj.wait();
 ? ? ? ? ? ? ? ? ? ?System.out.println("thread2 end + " + new Date(System.currentTimeMillis()));
 ? ? ? ? ? ? ?  } catch (InterruptedException e) {
 ? ? ? ? ? ? ? ? ? ?e.printStackTrace();
 ? ? ? ? ? ? ?  }
 ? ? ? ? ?  }
 ? ? ?  });
 ? ? ? ?thread2.start();
 ?  }
}

 ? ?Thread thread;
 ? ?void parkAndUnpark() {
 ? ? ? ?Thread thread2 = new Thread(() -> {
 ? ? ? ? ? ?System.out.println("thread2 start + " + new Date(System.currentTimeMillis()));
 ? ? ? ? ? ?thread.start();
 ? ? ? ? ? ?LockSupport.park(obj);
 ? ? ? ? ? ?System.out.println("Blocker info " + LockSupport.getBlocker(Thread.currentThread()));
 ? ? ? ? ? ?System.out.println("thread2 end + " + new Date(System.currentTimeMillis()));
 ? ? ?  });
 ? ? ? ?// 喚起 thread2
 ? ? ? ?Thread thread1 = new Thread(() -> {
 ? ? ? ? ? ?try {
 ? ? ? ? ? ? ? ?System.out.println("thread1 start + " + new Date(System.currentTimeMillis()));
 ? ? ? ? ? ? ? ?Thread.sleep(3000);
 ? ? ? ? ? ? ? ?System.out.println("Blocker info " + LockSupport.getBlocker(thread2));
 ? ? ? ? ? ? ? ?LockSupport.unpark(thread2);
 ? ? ? ? ? ? ? ?System.out.println("thread1 end + " + new Date(System.currentTimeMillis()));
 ? ? ? ? ?  } catch (InterruptedException e) {
 ? ? ? ? ? ? ? ?e.printStackTrace();
 ? ? ? ? ?  }
 ? ? ?  });
 ? ? ? ?thread = thread1;
 ? ? ? ?thread2.start();
 ?  }