/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You 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.apache.jackrabbit.core;
import java.util.concurrent.RejectedExecutionHandler;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.ScheduledThreadPoolExecutor;
import java.util.concurrent.ThreadFactory;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.concurrent.atomic.AtomicInteger;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
/**
* Thread pool used by the repository.
*/
class JackrabbitThreadPool extends ScheduledThreadPoolExecutor {
/**
* The logger instance for this class.
*/
private static final Logger log = LoggerFactory
.getLogger(JackrabbitThreadPool.class);
/**
* Size of the per-repository thread pool.
*/
private static final int size =
Runtime.getRuntime().availableProcessors() * 2;
/**
* The classloader used as the context classloader of threads in the pool.
*/
private static final ClassLoader loader =
JackrabbitThreadPool.class.getClassLoader();
/**
* Thread counter for generating unique names for the threads in the pool.
*/
private static final AtomicInteger counter = new AtomicInteger(1);
/**
* Thread factory for creating the threads in the pool
*/
private static final ThreadFactory factory = new ThreadFactory() {
public Thread newThread(Runnable runnable) {
int count = counter.getAndIncrement();
String name = "jackrabbit-pool-" + count;
Thread thread = new Thread(runnable, name);
thread.setDaemon(true);
if (thread.getPriority() != Thread.NORM_PRIORITY) {
thread.setPriority(Thread.NORM_PRIORITY);
}
thread.setContextClassLoader(loader);
return thread;
}
};
/**
* Handler for tasks for which no free thread is found within the pool.
*/
private static final RejectedExecutionHandler handler = new CallerRunsPolicy();
/**
* Property to control the value at which the thread pool starts to schedule
* the {@link LowPriorityTask} tasks for later execution.
*
* Set to <code>0</code> to disable the check
*
* Default value is 0 (check is disabled).
*
*/
public static final String MAX_LOAD_FOR_LOW_PRIORITY_TASKS_PROPERTY = "org.apache.jackrabbit.core.JackrabbitThreadPool.maxLoadForLowPriorityTasks";
/**
* @see #MAX_LOAD_FOR_LOW_PRIORITY_TASKS_PROPERTY
*/
private final static Integer maxLoadForLowPriorityTasks = getMaxLoadForLowPriorityTasks();
private static int getMaxLoadForLowPriorityTasks() {
final int defaultMaxLoad = 75;
int max = Integer.getInteger(MAX_LOAD_FOR_LOW_PRIORITY_TASKS_PROPERTY,
defaultMaxLoad);
if (max < 0 || max > 100) {
return defaultMaxLoad;
}
return max;
}
/**
* Queue where all the {@link LowPriorityTask} tasks go for later execution
*/
private final BlockingQueue<Runnable> lowPriorityTasksQueue = new LinkedBlockingQueue<Runnable>();
/**
* Tasks that handles the scheduling and the execution of
* {@link LowPriorityTask} tasks
*/
private final RetryLowPriorityTask retryTask;
/**
* Creates a new thread pool.
*/
public JackrabbitThreadPool() {
super(size, factory, handler);
retryTask = new RetryLowPriorityTask(this, lowPriorityTasksQueue);
}
@Override
public void execute(Runnable command) {
if (command instanceof LowPriorityTask) {
scheduleLowPriority(command);
return;
}
super.execute(command);
}
private void scheduleLowPriority(Runnable command) {
if (isOverDefinedMaxLoad()) {
lowPriorityTasksQueue.add(command);
retryTask.retryLater();
return;
}
super.execute(command);
}
/**
* compares the current load of the executor with the defined
* <code>{@link #maxLoadForLowPriorityTasks}</code> parameter.
*
* Used to determine if the executor can handle additional
* {@link LowPriorityTask} tasks.
*
* @return true if the load is under the
* <code>{@link #maxLoadForLowPriorityTasks}</code> parameter
*/
private boolean isOverDefinedMaxLoad() {
if (maxLoadForLowPriorityTasks == 0) {
return false;
}
double currentLoad = ((double) getActiveCount()) / getPoolSize() * 100;
return currentLoad > maxLoadForLowPriorityTasks;
}
/**
* TEST ONLY
*
* @return the number of low priority tasks that are waiting in the queue
*/
int getPendingLowPriorityTaskCount() {
return lowPriorityTasksQueue.size();
}
private static final class RetryLowPriorityTask implements Runnable {
/**
* schedule interval in ms for delayed tasks
*/
private static final int LATER_MS = 50;
private final JackrabbitThreadPool executor;
private final BlockingQueue<Runnable> lowPriorityTasksQueue;
/**
* flag to indicate that another execute has been scheduled or is
* currently running.
*/
private final AtomicBoolean retryPending;
public RetryLowPriorityTask(JackrabbitThreadPool executor,
BlockingQueue<Runnable> lowPriorityTasksQueue) {
this.executor = executor;
this.lowPriorityTasksQueue = lowPriorityTasksQueue;
this.retryPending = new AtomicBoolean(false);
}
public void retryLater() {
if (!retryPending.getAndSet(true)) {
executor.schedule(this, LATER_MS, TimeUnit.MILLISECONDS);
}
}
public void run() {
int count = 0;
while (!executor.isOverDefinedMaxLoad()) {
Runnable r = lowPriorityTasksQueue.poll();
if (r == null) {
log.debug("Executed {} low priority tasks.", count);
break;
}
count++;
executor.execute(r);
}
retryPending.set(false);
if (!lowPriorityTasksQueue.isEmpty()) {
log.debug(
"Executor is under load, will schedule {} remaining tasks for {} ms later",
lowPriorityTasksQueue.size(), LATER_MS);
retryLater();
}
}
}
}