Package org.eclipse.jetty.util

Class LeakDetector<T>

java.lang.Object
org.eclipse.jetty.util.component.AbstractLifeCycle
org.eclipse.jetty.util.LeakDetector<T>
Type Parameters:
T - the resource type.
All Implemented Interfaces:
Runnable, LifeCycle
public class LeakDetector<T> extends AbstractLifeCycle implements Runnable
A facility to detect improper usage of resource pools.

Resource pools usually have a method to acquire a pooled resource and a method to released it back to the pool.

To detect if client code acquires a resource but never releases it, the resource pool can be modified to use a LeakDetector. The modified resource pool should call acquired(Object) every time the method to acquire a resource is called, and released(Object) every time the method to release the resource is called. LeakDetector keeps track of these resources and invokes method leaked(org.eclipse.jetty.util.LeakDetector.LeakInfo) when it detects that a resource has been leaked (that is, acquired but never released).

To detect whether client code releases a resource without having acquired it, the resource pool can be modified to check the return value of released(Object): if false, it means that the resource was not acquired.

IMPLEMENTATION NOTES

This class relies on System.identityHashCode(Object) to create a unique id for each resource passed to acquired(Object) and released(Object). System.identityHashCode(Object) does not guarantee that it will not generate the same number for different objects, but in practice the chance of collision is rare.

LeakDetector uses PhantomReferences to detect leaks. PhantomReferences are enqueued in their ReferenceQueue after they have been garbage collected (differently from WeakReferences that are enqueued before). Since the resource is now garbage collected, LeakDetector checks whether it has been released and if not, it reports a leak. Using PhantomReferences is better than overriding Object.finalize() and works also in those cases where Object.finalize() is not overridable.