// Copyright (C) 2009 The Android Open Source Project
//
// 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.gerrit.git;

import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.Callable;
import java.util.concurrent.Delayed;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.RunnableScheduledFuture;
import java.util.concurrent.ScheduledThreadPoolExecutor;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;

/** Delayed execution of tasks using a background thread pool. */
public class WorkQueue {
  private static Executor pool;

  private static synchronized Executor getPool(final boolean autoStart) {
    if (autoStart && pool == null) {
      pool = new Executor(1);
    }
    return pool;
  }

  static void adviseThreadCount(final int callerWants) {
    final Executor p = getPool(true);
    p.setMaximumPoolSize(1 + callerWants);
    p.setCorePoolSize(1 + callerWants);
  }

  /** Get all of the tasks currently scheduled in the work queue. */
  public static Task<?>[] getTasks() {
    final Executor p = getPool(false);
    final Task<?>[] r;
    r = p != null ? p.toTaskArray() : new Task[] {};
    return r;
  }

  /**
   * Schedule a task to run at a later point in time.
   * 
   * @param task the task to invoke the {@code run()} method of later, on a
   *        background thread.
   * @param delay amount to wait before calling the task. May be 0 to request
   *        "as soon as possible".
   * @param unit time unit that {@code delay} is measured in.
   */
  public static void schedule(final Runnable task, final long delay,
      final TimeUnit unit) {
    getPool(true).schedule(task, delay, unit);
  }

  /** Shutdown the work queue, aborting any pending tasks that haven't started. */
  public static void terminate() {
    final ScheduledThreadPoolExecutor p = shutdown();
    if (p != null) {
      boolean isTerminated;
      do {
        try {
          isTerminated = p.awaitTermination(10, TimeUnit.SECONDS);
        } catch (InterruptedException ie) {
          isTerminated = false;
        }
      } while (!isTerminated);
    }
  }

  private static synchronized ScheduledThreadPoolExecutor shutdown() {
    final ScheduledThreadPoolExecutor p = pool;
    if (p != null) {
      p.shutdown();
      pool = null;
      return p;
    }
    return null;
  }

  private static class Executor extends ScheduledThreadPoolExecutor {
    private final List<Task<?>> active = new ArrayList<Task<?>>();

    Executor(final int corePoolSize) {
      super(corePoolSize);
    }

    @Override
    protected <V> RunnableScheduledFuture<V> decorateTask(
        final Runnable runnable, final RunnableScheduledFuture<V> task) {
      return new Task<V>(runnable, super.decorateTask(runnable, task));
    }

    @Override
    protected <V> RunnableScheduledFuture<V> decorateTask(
        final Callable<V> callable, final RunnableScheduledFuture<V> task) {
      throw new UnsupportedOperationException("Callable not implemented");
    }

    @Override
    protected void beforeExecute(Thread t, Runnable r) {
      super.beforeExecute(t, r);
      synchronized (active) {
        active.add((Task<?>) r);
      }
    }

    @Override
    protected void afterExecute(Runnable r, Throwable t) {
      super.afterExecute(r, t);
      synchronized (active) {
        active.remove(r);
      }
    }

    Task<?>[] toTaskArray() {
      final List<Task<?>> list = new ArrayList<Task<?>>();
      synchronized (active) {
        list.addAll(active);
      }
      for (final Runnable task : getQueue()) { // iterator is thread safe
        list.add((Task<?>) task);
      }
      return list.toArray(new Task<?>[list.size()]);
    }
  }

  /** A wrapper around a scheduled Runnable, as maintained in the queue. */
  public static class Task<V> implements RunnableScheduledFuture<V> {
    /**
     * Summarized status of a single task.
     * <p>
     * Tasks have the following state flow:
     * <ol>
     * <li>{@link #SLEEPING}: if scheduled with a non-zero delay.</li>
     * <li>{@link #READY}: waiting for an available worker thread.</li>
     * <li>{@link #RUNNING}: actively executing on a worker thread.</li>
     * <li>{@link #DONE}: finished executing, if not periodic.</li>
     * </ol>
     */
    public static enum State {
      // Ordered like this so ordinal matches the order we would
      // prefer to see tasks sorted in: done before running,
      // running before ready, ready before sleeping.
      //
      DONE, CANCELLED, RUNNING, READY, SLEEPING, OTHER;
    }

    private final Runnable runnable;
    private final RunnableScheduledFuture<V> task;
    private volatile boolean running;

    Task(Runnable runnable, RunnableScheduledFuture<V> task) {
      this.runnable = runnable;
      this.task = task;
    }

    /** Get the Runnable this task executes. */
    public Runnable getRunnable() {
      return runnable;
    }

    public State getState() {
      if (isDone() && !isPeriodic()) {
        return State.DONE;
      } else if (isRunning()) {
        return State.RUNNING;
      } else if (isCancelled()) {
        return State.CANCELLED;
      }

      final long delay = getDelay(TimeUnit.MILLISECONDS);
      if (delay <= 0) {
        return State.READY;
      } else if (0 < delay) {
        return State.SLEEPING;
      }

      return State.OTHER;
    }

    public boolean cancel(boolean mayInterruptIfRunning) {
      return task.cancel(mayInterruptIfRunning);
    }

    public int compareTo(Delayed o) {
      return task.compareTo(o);
    }

    public V get() throws InterruptedException, ExecutionException {
      return task.get();
    }

    public V get(long timeout, TimeUnit unit) throws InterruptedException,
        ExecutionException, TimeoutException {
      return task.get(timeout, unit);
    }

    public long getDelay(TimeUnit unit) {
      return task.getDelay(unit);
    }

    public boolean isCancelled() {
      return task.isCancelled();
    }

    public boolean isRunning() {
      return running;
    }

    public boolean isDone() {
      return task.isDone();
    }

    public boolean isPeriodic() {
      return task.isPeriodic();
    }

    public void run() {
      try {
        running = true;
        task.run();
      } finally {
        running = false;
      }
    }

    @Override
    public String toString() {
      return runnable.toString();
    }
  }
}

@@ -679,19 +679,67 @@
 va.util.
-Lis
+HashSet;%0Aimport java.util.List;%0Aimport java.util.Se
 t;%0Aimpor
@@ -2933,24 +2933,88 @@
  null;%0A  %7D%0A%0A
+    private final Set%3CTask%3C?%3E%3E active = new HashSet%3CTask%3C?%3E%3E();%0A
   private st
@@ -3074,75 +3074,8 @@
 or %7B
-%0A    private final List%3CTask%3C?%3E%3E active = new ArrayList%3CTask%3C?%3E%3E();
 %0A%0A  

Use a HashSet for the active tasks, rather than a List