RWLockDataStructure.java

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package com.sun.enterprise.resource.pool.datastructure;

import com.sun.enterprise.resource.allocator.ResourceAllocator;
import com.sun.enterprise.resource.ResourceHandle;
import com.sun.enterprise.resource.pool.ResourceHandler;
import com.sun.enterprise.resource.pool.datastructure.strategy.ResourceSelectionStrategy;
import com.sun.appserv.connectors.internal.api.PoolingException;
import com.sun.logging.LogDomains;

import java.util.concurrent.locks.ReentrantReadWriteLock;
import java.util.Iterator;
import java.util.ArrayList;
import java.util.logging.Level;
import java.util.logging.Logger;

/**
 * ReadWriteLock based datastructure for pool
 * @author Jagadish Ramu
 */
public class RWLockDataStructure implements DataStructure {

    private ResourceHandler handler;
    private ResourceSelectionStrategy strategy;
    private int maxSize;

    private final ArrayList<ResourceHandle> resources;
    private ReentrantReadWriteLock reentrantLock = new ReentrantReadWriteLock();
    private ReentrantReadWriteLock.ReadLock readLock = reentrantLock.readLock();
    private ReentrantReadWriteLock.WriteLock writeLock = reentrantLock.writeLock();

    protected final static Logger _logger =
            LogDomains.getLogger(RWLockDataStructure.class,LogDomains.RSR_LOGGER);

    public RWLockDataStructure(String parameters, int maxSize,
                                              ResourceHandler handler, String strategyClass) {
        resources = new ArrayList<ResourceHandle>((maxSize > 1000) ? 1000 : maxSize);
        this.maxSize = maxSize;
        this.handler = handler;
        initializeStrategy(strategyClass);
        if(_logger.isLoggable(Level.FINEST)) {
            _logger.log(Level.FINEST, "pool.datastructure.rwlockds.init");
        }
    }

    private void initializeStrategy(String strategyClass) {
        //TODO
    }

    /**
     * {@inheritDoc}
     */
    public int addResource(ResourceAllocator allocator, int count) throws PoolingException {
        int numResAdded = 0;
        writeLock.lock();
        //for now, coarser lock. finer lock needs "resources.size() < maxSize()" once more.
        try {
            for (int i = 0; i < count && resources.size() < maxSize; i++) {
                ResourceHandle handle = handler.createResource(allocator);
                resources.add(handle);
                numResAdded++;
            }
        } catch (Exception e) {
            PoolingException pe = new PoolingException(e.getMessage());
            pe.initCause(e);
            throw pe;
        } finally {
            writeLock.unlock();
        }
        return numResAdded;
    }

    /**
     * {@inheritDoc}
     */
    public ResourceHandle getResource() {
        readLock.lock();
        for(int i=0; i<resources.size(); i++){
            ResourceHandle h = resources.get(i);
            if (!h.isBusy()) {
                readLock.unlock();
                writeLock.lock();
                try {
                    if (!h.isBusy()) {
                        h.setBusy(true);
                        return h;
                    } else {
                        readLock.lock();
                        continue;
                    }
                }finally {
                    writeLock.unlock();
                }
            } else {
                continue;
            }
        }
        readLock.unlock();
        return null;
    }

    /**
     * {@inheritDoc}
     */
    public void removeResource(ResourceHandle resource) {
        boolean removed = false;
        writeLock.lock();
        try {
            removed = resources.remove(resource);
        } finally {
            writeLock.unlock();
        }
        if(removed) {
            handler.deleteResource(resource);
        }
    }

    /**
     * {@inheritDoc}
     */
    public void returnResource(ResourceHandle resource) {
        writeLock.lock();
        try{
            resource.setBusy(false);
        }finally{
            writeLock.unlock();
        }
    }

    /**
     * {@inheritDoc}
     */
    public int getFreeListSize() {
        //inefficient implementation.
        int free = 0;
        readLock.lock();
        try{
            Iterator it = resources.iterator();
            while (it.hasNext()) {
                ResourceHandle rh = (ResourceHandle)it.next();
                if(!rh.isBusy()){
                    free++;
                }
            }
        }finally{
            readLock.unlock();
        }
        return free;
    }

    /**
     * {@inheritDoc}
     */
    public void removeAll() {
        writeLock.lock();
        try {
            Iterator it = resources.iterator();
            while (it.hasNext()) {
                handler.deleteResource((ResourceHandle) it.next());
                it.remove();
            }
        } finally {
            writeLock.unlock();
        }
        resources.clear();
    }

    /**
     * {@inheritDoc}
     */
    public int getResourcesSize() {
        return resources.size();
    }

    /**
     * Set maxSize based on the new max pool size set on the connection pool 
     * during a reconfiguration. 
     * 
     * @param maxSize
     */
    public void setMaxSize(int maxSize) {
        this.maxSize = maxSize;
    }

    @Override
    public ArrayList<ResourceHandle> getAllResources() {
        throw new UnsupportedOperationException("Not supported yet.");
    }
}