| /* |
| * 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 com.google.android.exoplayer2.util; |
| |
| import static java.lang.Math.max; |
| |
| 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 = 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(); |
| } |
| } |
| } |