Class Task

Bolts/src/bolts/Task.java:28–641

Represents the result of an asynchronous operation. @param The type of the result of the task.

 *          The type of the result of the task.
 */
public class Task<TResult> {
  private static final ExecutorService backgroundExecutor = Executors.newCachedThreadPool();
  /**
   * An executor that runs a runnable inline (rather than scheduling it on a thread pool) as long as
   * the recursion depth is less than MAX_DEPTH. If the executor has recursed too deeply, it will
   * instead delegate to the backgroundExecutor in order to trim the stack.
   */
  private static final Executor immediateExecutor = new Executor() {
    private static final int MAX_DEPTH = 15;
    private ThreadLocal<Integer> executionDepth = new ThreadLocal<Integer>();

    /**
     * Increments the depth.
     * 
     * @return the new depth value.
     */
    private int incrementDepth() {
      Integer oldDepth = executionDepth.get();
      if (oldDepth == null) {
        oldDepth = 0;
      }
      int newDepth = oldDepth.intValue() + 1;
      executionDepth.set(newDepth);
      return newDepth;
    }

    /**
     * Decrements the depth.
     * 
     * @return the new depth value.
     */
    private int decrementDepth() {
      Integer oldDepth = executionDepth.get();
      if (oldDepth == null) {
        oldDepth = 0;
      }
      int newDepth = oldDepth.intValue() - 1;
      if (newDepth == 0) {
        executionDepth.remove();
      } else {
        executionDepth.set(newDepth);
      }
      return newDepth;
    }

    public void execute(Runnable command) {
      int depth = incrementDepth();
      try {
        if (depth <= MAX_DEPTH) {
          command.run();
        } else {
          backgroundExecutor.execute(command);
        }
      } finally {
        decrementDepth();
      }
    }
  };