108 lines
2.5 KiB
Java
108 lines
2.5 KiB
Java
package org.gcube.common.clients.stubs.jaxws;
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import java.util.LinkedHashMap;
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import java.util.concurrent.Callable;
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import java.util.concurrent.ConcurrentHashMap;
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import java.util.concurrent.locks.Lock;
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import java.util.concurrent.locks.ReentrantLock;
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import javax.xml.namespace.QName;
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import javax.xml.ws.Service;
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import org.slf4j.Logger;
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import org.slf4j.LoggerFactory;
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/**
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* Privately used by a {@link StubFactory}, caches {@link Service} instances for services with given names.
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* <p>
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* The cache is LRU and bounded at a maximum size of {@link LRUCache#max}. It is also thread-safe, though synchronisation
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* occurs on a per-key basis.
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*
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* @author Fabio Simeoni
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* @see StubFactory
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*/
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class StubCache {
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private static final Logger log = LoggerFactory.getLogger(StubCache.class);
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private volatile LRUCache cache = new LRUCache();
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//holds key locks for LRU map
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private ConcurrentHashMap<QName,Lock> nameLocks = new ConcurrentHashMap<QName, Lock>();
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Service get(QName name,Callable<Service> task) {
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//obtain a lock for current key
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Lock nameLock = lockFor(name);
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nameLock.lock();
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try {
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Service service = cache.get(name);
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if (service==null)
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try {
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service= task.call();
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log.trace("caching stub for "+name);
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cache.put(name,service);
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}
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catch(Exception e) {
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throw new RuntimeException("could not build service",e);
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}
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else {
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log.trace("using cached stub for "+name);
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}
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return service;
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}
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finally {
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nameLock.unlock();
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}
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}
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//helper
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private Lock lockFor(QName name) {
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Lock nameLock = nameLocks.get(name);
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//no need to create a new lock a priori
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if (nameLock==null) {
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Lock newLock = new ReentrantLock();
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//get name lock, creating it if it doesn't exist
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//this is where we first synchronise: second-come thread waits for new one to have put a lock
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//then it gets that same shared lock
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nameLock = nameLocks.putIfAbsent(name,newLock);
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nameLock = nameLock == null? newLock : nameLock;
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}
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return nameLock;
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}
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private class LRUCache extends LinkedHashMap<QName,Service> {
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private static final long serialVersionUID = 1L;
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public static final int max = 50;
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public LRUCache() {
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//use defaults, but indicate accessor-order as 3rd parameter (rather than default insertion order)
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super(16,.75f,true);
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}
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@Override
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protected boolean removeEldestEntry(java.util.Map.Entry<QName, Service> eldest) {
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if (size()>=max) {
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nameLocks.remove(eldest.getKey());
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return true;
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}
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return false;
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}
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}
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}
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