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package com.sun.enterprise.resource.pool.datastructure;
import com.sun.enterprise.resource.ResourceHandle;
import com.sun.enterprise.resource.allocator.ResourceAllocator;
import com.sun.appserv.connectors.internal.api.PoolingException;
import com.sun.enterprise.resource.pool.ResourceHandler;
import com.sun.enterprise.resource.pool.datastructure.strategy.ResourceSelectionStrategy;
import java.util.ArrayList;
import java.util.concurrent.Semaphore;
/**
* List based datastructure that can be used by connection pool <br>
*
* @author Jagadish Ramu
*/
public class ListDataStructure implements DataStructure {
private final ArrayList<ResourceHandle> free;
private final ArrayList<ResourceHandle> resources;
//Max Size of the datastructure.Depends mostly on the max-pool-size of
// the connection pool.
private int maxSize;
private final DynamicSemaphore dynSemaphore;
private ResourceHandler handler;
private ResourceSelectionStrategy strategy;
public ListDataStructure(String parameters, int maxSize, ResourceHandler handler, String strategyClass) {
resources = new ArrayList<ResourceHandle>((maxSize > 1000) ? 1000 : maxSize);
free = new ArrayList<ResourceHandle>((maxSize > 1000) ? 1000 : maxSize);
this.handler = handler;
initializeStrategy(strategyClass);
dynSemaphore = new DynamicSemaphore();
setMaxSize(maxSize);
}
/**
* Set maxSize based on the new max pool size set on the connection pool
* during a reconfiguration.
* 1. When permits contained within the dynamic semaphore are greater than 0,
* maxSize is increased and hence so many permits are released.
* 2. When permits contained within the dynamic semaphore are less than 0,
* maxSize has reduced to a smaller value. Hence so many permits are reduced
* from the semaphore's available limit for the subsequent resource requests
* to act based on the new configuration.
* @param newMaxSize
*/
public synchronized void setMaxSize(int newMaxSize) {
//Find currently open with the current maxsize
int permits = newMaxSize - this.maxSize;
if (permits == 0) {
//None are open
return;
} else if (permits > 0) {
//Case when no of permits are increased
this.dynSemaphore.release(permits);
} else {
//permits would be a -ve value
//Case when no of permits are to be reduced.
permits *= -1;
this.dynSemaphore.reducePermits(permits);
}
this.maxSize = newMaxSize;
}
private void initializeStrategy(String strategyClass) {
//TODO
}
/**
* creates a new resource and adds to the datastructure.
*
* @param allocator ResourceAllocator
* @param count Number (units) of resources to create
* @return int number of resources added
*/
public int addResource(ResourceAllocator allocator, int count) throws PoolingException {
int numResAdded = 0;
for (int i = 0; i < count && resources.size() < maxSize; i++) {
boolean lockAcquired = dynSemaphore.tryAcquire();
if(lockAcquired) {
try {
ResourceHandle handle = handler.createResource(allocator);
synchronized (resources) {
synchronized (free) {
free.add(handle);
resources.add(handle);
numResAdded++;
}
}
} catch (Exception e) {
dynSemaphore.release();
PoolingException pe = new PoolingException(e.getMessage());
pe.initCause(e);
throw pe;
}
}
}
return numResAdded;
}
/**
* get a resource from the datastructure
*
* @return ResourceHandle
*/
public ResourceHandle getResource() {
ResourceHandle resource = null;
if (strategy != null) {
resource = strategy.retrieveResource();
} else {
synchronized (free) {
if (free.size() > 0){
resource = free.remove(0);
}
}
}
return resource;
}
/**
* remove the specified resource from the datastructure
*
* @param resource ResourceHandle
*/
public void removeResource(ResourceHandle resource) {
boolean removed = false;
synchronized (resources) {
synchronized (free) {
free.remove(resource);
removed = resources.remove(resource);
}
}
if(removed) {
dynSemaphore.release();
handler.deleteResource(resource);
}
}
/**
* returns the resource to the datastructure
*
* @param resource ResourceHandle
*/
public void returnResource(ResourceHandle resource) {
synchronized (free) {
free.add(resource);
}
}
/**
* get the count of free resources in the datastructure
*
* @return int count
*/
public int getFreeListSize() {
return free.size();
}
/**
* remove & destroy all resources from the datastructure.
*/
public void removeAll() {
synchronized (resources) {
synchronized (free) {
while (resources.size() > 0) {
ResourceHandle handle = resources.remove(0);
free.remove(handle);
dynSemaphore.release();
handler.deleteResource(handle);
}
}
}
free.clear();
resources.clear();
}
/**
* get total number of resources in the datastructure
*
* @return int count
*/
public int getResourcesSize() {
return resources.size();
}
/**
* {@inheritDoc}
*/
@Override
public ArrayList<ResourceHandle> getAllResources() {
return this.resources;
}
/**
* Semaphore whose available permits change according to the
* changes in max-pool-size via a reconfiguration.
*/
private static final class DynamicSemaphore extends Semaphore {
DynamicSemaphore() {
//Default is 0
super(0);
}
@Override
protected void reducePermits(int size) {
super.reducePermits(size);
}
}
}