Class FutureTask

classpath/java/util/concurrent/FutureTask.java:15–169

import java.util.concurrent.atomic.AtomicReference;

public class FutureTask<T> implements RunnableFuture<T> {
  private enum State { New, Canceling, Canceled, Running, Done };
  
  private final AtomicReference<State> currentState;
  private final Callable<T> callable;
  private final Object notifyLock;
  private volatile Thread runningThread;
  private volatile T result;
  private volatile Throwable failure;
  
  public FutureTask(final Runnable r, final T result) {
    this(new Callable<T>() {
      @Override
      public T call() {
        r.run();
        
        return result;
      }
    });
  }
  
  public FutureTask(Callable<T> callable) {
    currentState = new AtomicReference<State>(State.New);
    this.callable = callable;
    notifyLock = new Object();
    runningThread = null;
    result = null;
    failure = null;
  }

  @Override
  public void run() {
    if (currentState.compareAndSet(State.New, State.Running)) {
      runningThread = Thread.currentThread();
      try {
        result = callable.call();
      } catch (Throwable t) {
        failure = t;
      } finally {
        if (currentState.compareAndSet(State.Running, State.Done) || 
            currentState.get() == State.Canceled) {
          /* in either of these conditions we either were not canceled 
           * or we already were interrupted.  The thread may or MAY NOT
           * be in an interrupted status depending on when it was 
           * interrupted and what the callable did with the state. 
           */
        } else {
          /* Should be in canceling state, so block forever till we are 
           * interrupted.  If state already transitioned into canceled 
           * and thus thread is in interrupted status, the exception should 
           * throw immediately on the sleep call.
           */
          try {
            Thread.sleep(Long.MAX_VALUE);
          } catch (InterruptedException e) {
            // expected
          }
        }