1 files changed, 119 insertions, 0 deletions
diff --git a/mobile/android/exoplayer2/src/main/java/org/mozilla/thirdparty/com/google/android/exoplayer2/util/PriorityTaskManager.java b/mobile/android/exoplayer2/src/main/java/org/mozilla/thirdparty/com/google/android/exoplayer2/util/PriorityTaskManager.java
new file mode 100644
index 0000000000..1067014b40
--- /dev/null
+++ b/mobile/android/exoplayer2/src/main/java/org/mozilla/thirdparty/com/google/android/exoplayer2/util/PriorityTaskManager.java
@@ -0,0 +1,119 @@
+/*
+ * Copyright (C) 2016 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 org.mozilla.thirdparty.com.google.android.exoplayer2.util;
+
+import java.io.IOException;
+import java.util.Collections;
+import java.util.PriorityQueue;
+
+/**
+ * Allows tasks with associated priorities to control how they proceed relative to one another.
+ * <p>
+ * A task should call {@link #add(int)} to register with the manager and {@link #remove(int)} to
+ * unregister. A registered task will prevent tasks of lower priority from proceeding, and should
+ * call {@link #proceed(int)}, {@link #proceedNonBlocking(int)} or {@link #proceedOrThrow(int)} each
+ * time it wishes to check whether it is itself allowed to proceed.
+ */
+public final class PriorityTaskManager {
+
+  /**
+   * Thrown when task attempts to proceed when another registered task has a higher priority.
+   */
+  public static class PriorityTooLowException extends IOException {
+
+    public PriorityTooLowException(int priority, int highestPriority) {
+      super("Priority too low [priority=" + priority + ", highest=" + highestPriority + "]");
+    }
+
+  }
+
+  private final Object lock = new Object();
+
+  // Guarded by lock.
+  private final PriorityQueue<Integer> queue;
+  private int highestPriority;
+
+  public PriorityTaskManager() {
+    queue = new PriorityQueue<>(10, Collections.reverseOrder());
+    highestPriority = Integer.MIN_VALUE;
+  }
+
+  /**
+   * Register a new task. The task must call {@link #remove(int)} when done.
+   *
+   * @param priority The priority of the task. Larger values indicate higher priorities.
+   */
+  public void add(int priority) {
+    synchronized (lock) {
+      queue.add(priority);
+      highestPriority = Math.max(highestPriority, priority);
+    }
+  }
+
+  /**
+   * Blocks until the task is allowed to proceed.
+   *
+   * @param priority The priority of the task.
+   * @throws InterruptedException If the thread is interrupted.
+   */
+  public void proceed(int priority) throws InterruptedException {
+    synchronized (lock) {
+      while (highestPriority != priority) {
+        lock.wait();
+      }
+    }
+  }
+
+  /**
+   * A non-blocking variant of {@link #proceed(int)}.
+   *
+   * @param priority The priority of the task.
+   * @return Whether the task is allowed to proceed.
+   */
+  public boolean proceedNonBlocking(int priority) {
+    synchronized (lock) {
+      return highestPriority == priority;
+    }
+  }
+
+  /**
+   * A throwing variant of {@link #proceed(int)}.
+   *
+   * @param priority The priority of the task.
+   * @throws PriorityTooLowException If the task is not allowed to proceed.
+   */
+  public void proceedOrThrow(int priority) throws PriorityTooLowException {
+    synchronized (lock) {
+      if (highestPriority != priority) {
+        throw new PriorityTooLowException(priority, highestPriority);
+      }
+    }
+  }
+
+  /**
+   * Unregister a task.
+   *
+   * @param priority The priority of the task.
+   */
+  public void remove(int priority) {
+    synchronized (lock) {
+      queue.remove(priority);
+      highestPriority = queue.isEmpty() ? Integer.MIN_VALUE : Util.castNonNull(queue.peek());
+      lock.notifyAll();
+    }
+  }
+
+}