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// Copyright Vespa.ai. 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 java.util.Arrays;
import java.util.HashMap;
import java.util.Map;
import java.util.logging.Level;
import java.util.logging.Logger;
/**
* Does reference counting by putting stacktraces in a map together with an optional context.
* Intended only for debugging as it is slow.
* Used if system property jdisc.debug.resources=stack
*
* @author baldersheim
*/
public class DebugReferencesWithStack implements References {
private static final Logger log = Logger.getLogger(DebugReferencesWithStack.class.getName());
private final Map<Throwable, Object> activeReferences = new HashMap<>();
private final DestructableResource resource;
private final DebugResourceReference initialreference;
public DebugReferencesWithStack(DestructableResource resource) {
final Throwable referenceStack = new Throwable();
this.activeReferences.put(referenceStack, this);
this.resource = resource;
initialreference = new DebugResourceReference(this, referenceStack);
}
@Override
public void release() {
initialreference.close();
}
@Override
public int referenceCount() {
synchronized (activeReferences) {
return activeReferences.size();
}
}
@Override
public ResourceReference refer(Object context) {
final Throwable referenceStack = new Throwable();
synchronized (activeReferences) {
if (activeReferences.isEmpty()) {
throw new IllegalStateException("Object is already destroyed, no more new references may be created."
+ " State={ " + currentState() + " }");
}
activeReferences.put(referenceStack, context);
}
log.log(Level.FINE, referenceStack, () ->
getClass().getName() + "@" + System.identityHashCode(this) + ".refer(): state={ " + currentState() + " }");
return new DebugResourceReference(this, referenceStack);
}
private void removeReferenceStack(final Throwable referenceStack, final Throwable releaseStack) {
final boolean doDestroy;
synchronized (activeReferences) {
final boolean wasThere = activeReferences.containsKey(referenceStack);
activeReferences.remove(referenceStack);
if (!wasThere) {
throw new IllegalStateException("Reference is already released and can only be released once."
+ " reference=" + Arrays.toString(referenceStack.getStackTrace())
+ ". State={ " + currentState() + "}");
}
doDestroy = activeReferences.isEmpty();
log.log(Level.FINE, releaseStack,
() -> getClass().getName() + "@" + System.identityHashCode(this) + " release: state={ " + currentState() + " }");
}
if (doDestroy) {
resource.close();
}
}
@Override
public String currentState() {
return "Active references: " + makeListOfActiveReferences();
}
private String makeListOfActiveReferences() {
final StringBuilder builder = new StringBuilder();
builder.append("[");
synchronized (activeReferences) {
for (var activeReference : activeReferences.entrySet()) {
builder.append(" ");
builder.append(Arrays.toString(activeReference.getKey().getStackTrace()));
}
}
builder.append(" ]");
return builder.toString();
}
private static class DebugResourceReference extends CloseableOnce {
private final DebugReferencesWithStack resource;
private final Throwable referenceStack;
public DebugResourceReference(DebugReferencesWithStack resource, final Throwable referenceStack) {
this.resource = resource;
this.referenceStack = referenceStack;
}
@Override
final void onClose() {
final Throwable releaseStack = new Throwable();
resource.removeReferenceStack(referenceStack, releaseStack);
}
@Override
final References getReferences() { return resource; }
}
}
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