Class LockSupport

classpath/java/util/concurrent/locks/LockSupport.java:15–85

import sun.misc.Unsafe;

public class LockSupport {
  private LockSupport() {
    // can't construct
  }
  
  private static final Unsafe unsafe;
  private static final long parkBlockerOffset;
  
  static {
    unsafe = Unsafe.getUnsafe();
    try {
      parkBlockerOffset = unsafe.objectFieldOffset(Thread.class.getDeclaredField("parkBlocker"));
    } catch (Exception ex) { 
      throw new Error(ex);
    }
  }
  
  public static void unpark(Thread thread) {
    if (thread != null) {
      unsafe.unpark(thread);
    }
  }
  
  public static void park(Object blocker) {
    doParkNanos(blocker, 0L);
  }
  
  public static void parkNanos(Object blocker, long nanos) {
    if (nanos <= 0) {
      return;
    }
    
    doParkNanos(blocker, nanos);
  }
  
  private static void doParkNanos(Object blocker, long nanos) {
    Thread t = Thread.currentThread();
    unsafe.putObject(t, parkBlockerOffset, blocker);
    unsafe.park(false, nanos);
    unsafe.putObject(t, parkBlockerOffset, null);
  }
  
  public static void parkUntil(Object blocker, long deadline) {
    Thread t = Thread.currentThread();
    unsafe.putObject(t, parkBlockerOffset, blocker);
    unsafe.park(true, deadline);
    unsafe.putObject(t, parkBlockerOffset, null);
  }
  
  public static Object getBlocker(Thread t) {
    if (t == null) {
      throw new NullPointerException();
    }
    
    return unsafe.getObjectVolatile(t, parkBlockerOffset);
  }
  
  public static void park() {