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// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
package com.yahoo.jdisc.refcount;
import com.yahoo.jdisc.ResourceReference;
import com.yahoo.jdisc.SharedResource;
import java.util.concurrent.atomic.AtomicInteger;
/**
* Does reference counting by using atomic counting of references
* Default in production
*
* @author baldersheim
*/
public class ReferencesByCount implements References {
private final AtomicInteger refCount;
private final DestructableResource resource;
private final NoDebugResourceReference initialReference;
public ReferencesByCount(DestructableResource resource) {
refCount = new AtomicInteger(1);
this.resource = resource;
initialReference = new NoDebugResourceReference(this);
}
@Override
public void release() {
initialReference.close();
}
@Override
public int referenceCount() {
return refCount.get();
}
@Override
public ResourceReference refer(Object context) {
addRef(1);
return new NoDebugResourceReference(this);
}
@Override
public String currentState() {
return "Active references: " + refCount.get() + "."
+ " Resource reference debugging is turned off. Consider toggling the "
+ SharedResource.SYSTEM_PROPERTY_NAME_DEBUG
+ " system property to get debugging assistance with reference tracking.";
}
private void removeRef() {
int refCount = addRef(-1);
if (refCount == 0) {
resource.close();
}
}
private int addRef(int value) {
while (true) {
int prev = refCount.get();
if (prev == 0) {
throw new IllegalStateException(getClass().getName() + ".addRef(" + value + "):"
+ " Object is already destroyed."
+ " Consider toggling the " + SharedResource.SYSTEM_PROPERTY_NAME_DEBUG
+ " system property to get debugging assistance with reference tracking.");
}
int next = prev + value;
if (refCount.compareAndSet(prev, next)) {
return next;
}
}
}
private static class NoDebugResourceReference extends CloseableOnce {
private final ReferencesByCount resource;
NoDebugResourceReference(final ReferencesByCount resource) {
this.resource = resource;
}
@Override final void onClose() { resource.removeRef(); }
@Override References getReferences() { return resource; }
}
}
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