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/*
* 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();
}
}
}
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