Class Signal

src/Deferred.java:1207–1226

Callback to wake us up when this Deferred is running. We will wait() on the intrinsic condition of this callback.

   * We will wait() on the intrinsic condition of this callback.
   */
  static final class Signal implements Callback<Object, Object> {
    // When the callback triggers, it'll replace the reference in this
    // array to something other than `this' -- since the result cannot
    // possibly be `this'.
    Object result = this;

    private final String thread = Thread.currentThread().getName();

    public Object call(final Object arg) {
      synchronized (this) {
        result = arg;
        super.notify();  // Guaranteed to have only 1 thread wait()ing.
      }
      return arg;
    }

    public String toString() {
      return "wakeup thread " + thread;
    }
  };

  /**
   * Executes all the callbacks in the current chain.