Merge pull request #46 from llIlll/extend_future

[ISSUE42]Add cancel method to Future

Author: duhenglucky

openmessaging-api/src/main/java/io/openmessaging/Future.java

@@ -32,6 +32,29 @@
  * @since OMS 1.0.0
  */
 public interface Future<V> {
+    /**
+     * Attempts to cancel execution of this task.  This attempt will
+     * fail if the task has already completed, has already been cancelled,
+     * or could not be cancelled for some other reason. If successful,
+     * and this task has not started when {@code cancel} is called,
+     * this task should never run.  If the task has already started,
+     * then the {@code mayInterruptIfRunning} parameter determines
+     * whether the thread executing this task should be interrupted in
+     * an attempt to stop the task.
+     *
+     * <p>After this method returns, subsequent calls to {@link #isDone} will
+     * always return {@code true}.  Subsequent calls to {@link #isCancelled}
+     * will always return {@code true} if this method returned {@code true}.
+     *
+     * @param mayInterruptIfRunning {@code true} if the thread executing this
+     * task should be interrupted; otherwise, in-progress tasks are allowed
+     * to complete
+     * @return {@code false} if the task could not be cancelled,
+     * typically because it has already completed normally;
+     * {@code true} otherwise
+     */
+    boolean cancel(boolean mayInterruptIfRunning);
+
     /**
      * Returns {@code true} if this task was cancelled before it completed normally.
      *