1 files changed, 245 insertions, 0 deletions
diff --git a/gerrit-server/src/main/java/com/google/gerrit/server/git/WorkQueue.java b/gerrit-server/src/main/java/com/google/gerrit/server/git/WorkQueue.java
new file mode 100644
index 0000000000..51f5c99c22
--- /dev/null
+++ b/gerrit-server/src/main/java/com/google/gerrit/server/git/WorkQueue.java
@@ -0,0 +1,245 @@
+// 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.server.git;
+
+import com.google.inject.Singleton;
+
+import java.util.ArrayList;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Set;
+import java.util.concurrent.Callable;
+import java.util.concurrent.CopyOnWriteArrayList;
+import java.util.concurrent.Delayed;
+import java.util.concurrent.ExecutionException;
+import java.util.concurrent.Executors;
+import java.util.concurrent.RunnableScheduledFuture;
+import java.util.concurrent.ScheduledThreadPoolExecutor;
+import java.util.concurrent.ThreadFactory;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.TimeoutException;
+import java.util.concurrent.atomic.AtomicInteger;
+
+/** Delayed execution of tasks using a background thread pool. */
+@Singleton
+public class WorkQueue {
+  private Executor defaultQueue;
+  private final CopyOnWriteArrayList<Executor> queues =
+      new CopyOnWriteArrayList<Executor>();
+
+  /** Get the default work queue, for miscellaneous tasks. */
+  public synchronized Executor getDefaultQueue() {
+    if (defaultQueue == null) {
+      defaultQueue = createQueue(1, "WorkQueue");
+    }
+    return defaultQueue;
+  }
+
+  /** Create a new executor queue with one thread. */
+  public Executor createQueue(final int poolsize, final String prefix) {
+    final Executor r = new Executor(poolsize, prefix);
+    r.setContinueExistingPeriodicTasksAfterShutdownPolicy(false);
+    r.setExecuteExistingDelayedTasksAfterShutdownPolicy(false);
+    queues.add(r);
+    return r;
+  }
+
+  /** Get all of the tasks currently scheduled in any work queue. */
+  public List<Task<?>> getTasks() {
+    final List<Task<?>> r = new ArrayList<Task<?>>();
+    for (final Executor e : queues) {
+      e.addAllTo(r);
+    }
+    return r;
+  }
+
+  /** Shutdown all queues, aborting any pending tasks that haven't started. */
+  public void shutdown() {
+    for (final Executor p : queues) {
+      p.shutdown();
+      boolean isTerminated;
+      do {
+        try {
+          isTerminated = p.awaitTermination(10, TimeUnit.SECONDS);
+        } catch (InterruptedException ie) {
+          isTerminated = false;
+        }
+      } while (!isTerminated);
+    }
+    queues.clear();
+  }
+
+  /** An isolated queue. */
+  public static class Executor extends ScheduledThreadPoolExecutor {
+    private final Set<Task<?>> active = new HashSet<Task<?>>();
+
+    Executor(final int corePoolSize, final String prefix) {
+      super(corePoolSize, new ThreadFactory() {
+        private final ThreadFactory parent = Executors.defaultThreadFactory();
+        private final AtomicInteger tid = new AtomicInteger(1);
+
+        @Override
+        public Thread newThread(final Runnable task) {
+          final Thread t = parent.newThread(task);
+          t.setName(prefix + "-thread-" + tid.getAndIncrement());
+          return t;
+        }
+      });
+    }
+
+    @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);
+      }
+    }
+
+    void addAllTo(final List<Task<?>> list) {
+      synchronized (active) {
+        list.addAll(active);
+      }
+      for (final Runnable task : getQueue()) { // iterator is thread safe
+        list.add((Task<?>) task);
+      }
+    }
+  }
+
+  /** 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();
+    }
+  }
+}