com.yahoo.jdisc.SharedResource Maven / Gradle / Ivy
// Copyright Vespa.ai. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
package com.yahoo.jdisc;
import com.yahoo.jdisc.application.ContainerActivator;
import com.yahoo.jdisc.application.ContainerBuilder;
import com.yahoo.jdisc.application.DeactivatedContainer;
import com.yahoo.jdisc.handler.RequestHandler;
import com.yahoo.jdisc.service.ClientProvider;
import com.yahoo.jdisc.service.ServerProvider;
/**
* This interface defines a reference counted resource. This is the parent interface of {@link RequestHandler},
* {@link ClientProvider} and {@link ServerProvider}, and is used by jDISC to appropriately signal resources as they
* become candidates for deallocation. As a {@link ContainerBuilder} is {@link
* ContainerActivator#activateContainer(ContainerBuilder) activated}, all its components are {@link #refer() retained}
* by that {@link Container}. Once a {@link DeactivatedContainer} terminates, all of that Container's components are
* {@link ResourceReference#close() released}. This resource tracking allows an Application to implement a significantly
* simpler scheme for managing its resources than would otherwise be possible.
*
* Objects are created with an initial reference count of 1, representing the reference held by the object creator.
*
*
You should not really think about the management of resources in terms of reference counting, instead think of it
* in terms of resource ownership. You retain a resource to prevent it from being destroyed while you are using it, and
* you release a resource once you are done using it.
*
* @author Simon Thoresen Hult
*/
public interface SharedResource {
String SYSTEM_PROPERTY_NAME_DEBUG = "jdisc.debug.resources";
enum Debug {NO, SIMPLE, STACK}
Debug DEBUG = valueOfDebug();
private static Debug valueOfDebug() {
String val = System.getProperty(SYSTEM_PROPERTY_NAME_DEBUG);
if (val != null) {
val = val.toUpperCase();
if (Boolean.valueOf(val)) return Debug.SIMPLE;
try {
return Debug.valueOf(val);
} catch (IllegalArgumentException e) { }
}
return Debug.SIMPLE;
}
/**
* Creates a reference to this resource. You call this method to prevent an object from being
* destroyed until you have finished using it.
*
* You MUST keep the returned {@link ResourceReference} object and release the reference by calling
* {@link ResourceReference#close()} on it. A reference created by this method can NOT be released by calling
* {@link #release()}.
*
* @see ResourceReference#close()
*/
default ResourceReference refer() {
return refer(null);
}
/**
* Creates a reference to this resource. You call this method to prevent an object from being
* destroyed until you have finished using it. You can attach a context that will live as long as the reference.
*
* @param context A context to be associated with the reference. It should give some clue as to who referenced it.
* You MUST keep the returned {@link ResourceReference} object and release the reference by calling
* {@link ResourceReference#close()} on it. A reference created by this method can NOT be released by calling
* {@link #release()}.
*
* @see ResourceReference#close()
*/
default ResourceReference refer(Object context) {
return refer();
}
/**
* Releases the "main" reference to this resource (the implicit reference due to creation of the object).
*
* References obtained by calling {@link #refer()} must be released by calling {@link ResourceReference#close()}
* on the {@link ResourceReference} returned from {@link #refer()}, NOT by calling this method. You call this
* method once you are done using an object that you have previously caused instantiation of.
*
* @see ResourceReference
*/
void release();
}