ThreadPoolManager.java

/**
 * Copyright (c) 2014-2017 by the respective copyright holders.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 */
package org.eclipse.smarthome.core.common;

import java.util.Map;
import java.util.Map.Entry;
import java.util.WeakHashMap;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.ScheduledThreadPoolExecutor;
import java.util.concurrent.ThreadFactory;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicInteger;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * <p>
 * This class provides a general mechanism to create thread pools. In general, no code of Eclipse SmartHome
 * should deal with its own pools, but rather use this class.
 * The created thread pools have named threads, so that it is easy to find them in the debugger. Additionally, it is
 * possible to configure the pool sizes through the configuration admin service, so that solutions have the chance to
 * tweak the pool sizes according to their needs.
 * </p>
 * <p>
 * The configuration can be done as
 * <br/>
 * {@code org.eclipse.smarthome.threadpool:<poolName>=<poolSize>}
 * <br/>
 * All threads will time out after {@link THREAD_TIMEOUT}.
 * </p>
 *
 * @author Kai Kreuzer - Initial contribution
 *
 */
public class ThreadPoolManager {

    private final static Logger logger = LoggerFactory.getLogger(ThreadPoolManager.class);

    protected static final int DEFAULT_THREAD_POOL_SIZE = 5;

    protected static final long THREAD_TIMEOUT = 65L;
    protected static final long THREAD_MONITOR_SLEEP = 60000;

    static protected Map<String, ExecutorService> pools = new WeakHashMap<>();

    static private Map<String, Integer> configs = new ConcurrentHashMap<>();

    protected void activate(Map<String, Object> properties) {
        modified(properties);
    }

    protected void modified(Map<String, Object> properties) {
        for (Entry<String, Object> entry : properties.entrySet()) {
            if (entry.getKey().equals("service.pid") || entry.getKey().equals("component.id")
                    || entry.getKey().equals("component.name")) {
                continue;
            }
            String poolName = entry.getKey();
            Object config = entry.getValue();
            if (config == null) {
                configs.remove(poolName);
            }
            if (config instanceof String) {
                try {
                    Integer poolSize = Integer.valueOf((String) config);
                    configs.put(poolName, poolSize);
                    ThreadPoolExecutor pool = (ThreadPoolExecutor) pools.get(poolName);
                    if (pool instanceof ScheduledThreadPoolExecutor) {
                        pool.setCorePoolSize(poolSize);
                        logger.debug("Updated scheduled thread pool '{}' to size {}",
                                new Object[] { poolName, poolSize });
                    } else if (pool instanceof QueueingThreadPoolExecutor) {
                        pool.setMaximumPoolSize(poolSize);
                        logger.debug("Updated queuing thread pool '{}' to size {}",
                                new Object[] { poolName, poolSize });
                    }
                } catch (NumberFormatException e) {
                    logger.warn("Ignoring invalid configuration for pool '{}': {} - value must be an integer",
                            new Object[] { poolName, config });
                    continue;
                }
            }
        }
    }

    /**
     * Returns an instance of a scheduled thread pool service. If it is the first request for the given pool name, the
     * instance is newly created.
     *
     * @param poolName a short name used to identify the pool, e.g. "discovery"
     * @return an instance to use
     */
    static public ScheduledExecutorService getScheduledPool(String poolName) {
        ExecutorService pool = pools.get(poolName);
        if (pool == null) {
            synchronized (pools) {
                // do a double check if it is still null or if another thread might have created it meanwhile
                pool = pools.get(poolName);
                if (pool == null) {
                    int cfg = getConfig(poolName);
                    pool = Executors.newScheduledThreadPool(cfg, new NamedThreadFactory(poolName));
                    ((ThreadPoolExecutor) pool).setKeepAliveTime(THREAD_TIMEOUT, TimeUnit.SECONDS);
                    ((ThreadPoolExecutor) pool).allowCoreThreadTimeOut(true);
                    pools.put(poolName, pool);
                    logger.debug("Created scheduled thread pool '{}' of size {}", new Object[] { poolName, cfg });
                }
            }
        }
        if (pool instanceof ScheduledExecutorService) {
            return (ScheduledExecutorService) pool;
        } else {
            throw new IllegalArgumentException("Pool " + poolName + " is not a scheduled pool!");
        }
    }

    /**
     * Returns an instance of a cached thread pool service. If it is the first request for the given pool name, the
     * instance is newly created.
     *
     * @param poolName a short name used to identify the pool, e.g. "discovery"
     * @return an instance to use
     */
    static public ExecutorService getPool(String poolName) {
        ExecutorService pool = pools.get(poolName);
        if (pool == null) {
            synchronized (pools) {
                // do a double check if it is still null or if another thread might have created it meanwhile
                pool = pools.get(poolName);
                if (pool == null) {
                    int cfg = getConfig(poolName);
                    pool = QueueingThreadPoolExecutor.createInstance(poolName, cfg);
                    ((ThreadPoolExecutor) pool).setKeepAliveTime(THREAD_TIMEOUT, TimeUnit.SECONDS);
                    ((ThreadPoolExecutor) pool).allowCoreThreadTimeOut(true);
                    pools.put(poolName, pool);
                    logger.debug("Created thread pool '{}' with size {}", new Object[] { poolName, cfg });
                }
            }
        }
        return pool;
    }

    protected static int getConfig(String poolName) {
        Integer cfg = configs.get(poolName);
        return (cfg != null) ? cfg : DEFAULT_THREAD_POOL_SIZE;
    }

    /**
     * This is a normal thread factory, which adds a named prefix to all created threads.
     */
    protected static class NamedThreadFactory implements ThreadFactory {

        protected final ThreadGroup group;
        protected final AtomicInteger threadNumber = new AtomicInteger(1);
        protected final String namePrefix;
        protected final String name;

        public NamedThreadFactory(String threadPool) {
            this.name = threadPool;
            this.namePrefix = "ESH-" + threadPool + "-";
            SecurityManager s = System.getSecurityManager();
            group = (s != null) ? s.getThreadGroup() : Thread.currentThread().getThreadGroup();
        }

        @Override
        public Thread newThread(Runnable r) {
            Thread t = new Thread(group, r, namePrefix + threadNumber.getAndIncrement(), 0);
            if (!t.isDaemon()) {
                t.setDaemon(true);
            }
            if (t.getPriority() != Thread.NORM_PRIORITY) {
                t.setPriority(Thread.NORM_PRIORITY);
            }

            return t;
        }

        public String getName() {
            return name;
        }
    }

}