src/test/java/com/google/devtools/build/lib/shell/SimpleKillableObserver.java

// Copyright 2014 The Bazel Authors. All rights reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//    http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package com.google.devtools.build.lib.shell;

/**
 * A simple implementation of {@link KillableObserver} which can be told explicitly to kill its
 * {@link Killable} by calling {@link #kill()}. This is the sort of functionality that callers might
 * expect to find available on the {@link Command} class.</p>
 *
 * <p>Note that this class can only observe one {@link Killable} at a time; multiple instances
 * should be used for concurrent calls to {@link Command#execute}.
 */
final class SimpleKillableObserver implements KillableObserver {
  private Killable killable;

  @Override
  public synchronized void startObserving(final Killable killable) {
    this.killable = killable;
  }

  @Override
  public synchronized void stopObserving(final Killable killable) {
    if (!this.killable.equals(killable)) {
      throw new IllegalStateException("start/stopObservering called with " +
                                      "different Killables");
    }
    this.killable = null;
  }

  public synchronized void kill() {
    if (killable != null) {
      killable.kill();
    }
  }
}