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An extremely fast object pool with zero dependencies
There is a newer version: 1.0.3
package com.haiwanwan.common.objectpool;

import java.util.concurrent.TimeUnit;

/**
 * @author Daniel
 */
public class ObjectPool {

    protected final PoolConfig config;
    protected final ObjectFactory factory;
    protected final ObjectPoolPartition[] partitions;
    private final Scavenger scavenger;
    private volatile boolean shuttingDown;

    public ObjectPool(PoolConfig poolConfig, ObjectFactory objectFactory) {
        this.config = poolConfig;
        this.factory = objectFactory;
        this.partitions = new ObjectPoolPartition[config.getPartitionSize()];
        try {
            for (int i = 0; i < config.getPartitionSize(); i++) {
                partitions[i] = new ObjectPoolPartition<>(i, config, objectFactory);
            }
        } catch (InterruptedException e) {
            throw new RuntimeException(e);
        }
        this.scavenger = new Scavenger();
        this.scavenger.start();
    }

    public Poolable borrowObject() {
        return borrowObject(true);
    }

    public Poolable borrowObject(boolean blocking) {
        for (int i = 0; i < 3; i++) { // try at most three times
            Poolable result = getObject(blocking);
            if (factory.validate(result.getObject())) {
                return result;
            } else {
                this.partitions[result.getPartition()].decreaseObject(result);
            }
        }
        throw new RuntimeException("Cannot find a valid object");
    }

    private Poolable getObject(boolean blocking) {
        if (shuttingDown) {
            throw new IllegalStateException("Your pool is shutting down");
        }
        int partition = (int) (Thread.currentThread().getId() % this.config.getPartitionSize());
        ObjectPoolPartition subPool = this.partitions[partition];
        Poolable freeObject = subPool.getObjectQueue().poll();
        if (freeObject == null) {
            // increase objects and return one, it will return null if reach max size
            subPool.increaseObjects(1);
            try {
                if (blocking) {
                    freeObject = subPool.getObjectQueue().take();
                } else {
                    freeObject = subPool.getObjectQueue().poll(config.getMaxWaitMilliseconds(), TimeUnit.MILLISECONDS);
                    if (freeObject == null) {
                        throw new RuntimeException("Cannot get a free object from the pool");
                    }
                }
            } catch (InterruptedException e) {
                throw new RuntimeException(e); // will never happen
            }
        }
        freeObject.setLastAccessTs(System.currentTimeMillis());
        return freeObject;
    }

    public void returnObject(Poolable obj) {
        ObjectPoolPartition subPool = this.partitions[obj.getPartition()];
        try {
            subPool.getObjectQueue().put(obj);
            Log.debug("return object: queue size:" + subPool.getObjectQueue().size() + ", partition id:" + obj.getPartition());
        } catch (InterruptedException e) {
            throw new RuntimeException(e); // impossible for now
        }
    }

    public void close() {
        shuttingDown = true;
        //TODO: gracefully destroy all objects in the pool
    }

    public int getSize() {
        int size = 0;
        for (ObjectPoolPartition subPool : partitions) {
            size += subPool.getTotalCount();
        }
        return size;
    }

    public synchronized int shutdown() throws InterruptedException {
        shuttingDown = true;
        int removed = 0;
        scavenger.interrupt();
        scavenger.join();
        for (ObjectPoolPartition partition : partitions) {
            removed += partition.shutdown();
        }
        return removed;
    }

    private class Scavenger extends Thread {

        @Override
        public void run() {
            int partition = 0;
            while (!ObjectPool.this.shuttingDown) {
                try {
                    Thread.sleep(config.getScavengeIntervalMilliseconds());
                    partition = ++partition % config.getPartitionSize();
                    Log.debug("scavenge sub pool ",  partition);
                    partitions[partition].scavenge();
                } catch (InterruptedException e) {
                }
            }
        }

    }
}