Java provides a way to perform cleanup tasks before an object is garbage collected through finalization. Finalization allows you to override the finalize() method in your class to define the cleanup logic. However, finalization can have some pitfalls and is generally considered to be error-prone.

In this blog post, we will explore how the Shenandoah garbage collector (GC) handles finalization and weak references, and discuss the best practices to deal with finalization in Shenandoah.

Finalization and Shenandoah GC

Shenandoah GC is a low-pause garbage collector that is designed to minimize the impact of garbage collection on application throughput. It provides concurrent garbage collection cycles, significantly reducing pause times.

However, finalization adds complexity to the garbage collection process. When an object is being finalized, Shenandoah GC needs to stop all concurrent work and finalize the object to maintain object semantics.

Limitations of Finalization with Shenandoah GC

While finalization is supported by Shenandoah GC, there are a few limitations to be aware of:

1. Pause Time: Finalization introduces additional pause time as Shenandoah GC needs to suspend all concurrent threads to perform finalization. This can impact the overall pause time target of Shenandoah GC.

2. Finalization Order: The order in which objects are finalized is not guaranteed. This means if object A has a reference to object B, there is no guarantee that object B will be finalized before object A.

3. Object Resurrection: If an object resurrects itself in the finalize() method by creating a strong reference to itself or another object, it will prevent the object from being garbage collected. This can lead to memory leaks and unexpected behavior.

Weak References and Shenandoah GC

Java provides weak references that allow objects to be referenced weakly, meaning garbage collection can collect them even if there are strong references pointing to them. Weak references are commonly used for implementing caches, object pools, and other memory-sensitive data structures.

Shenandoah GC handles weak references efficiently. When a weakly referenced object becomes unreachable, the GC will clear the weak reference immediately during the concurrent cycle. This means that weakly referenced objects don’t need to go through the finalization process and can be garbage collected without any additional pausing.

Best Practices for Finalization with Shenandoah GC

Considering the limitations of finalization and the efficient handling of weak references by Shenandoah GC, it is recommended to avoid using finalization if possible. Instead, use alternative approaches for resource cleanup such as try-with-resources or explicit cleanup methods.

In cases where finalization is required, follow these best practices:

1. Minimize Finalization Usage: Only use finalization when absolutely necessary, as it adds complexity and potential performance overhead.

2. Avoid Object Resurrection: Ensure that objects being finalized do not resurrect themselves or other objects by creating strong references.

3. Use Weak References: If possible, use weak references instead of finalization to implement cleanup logic. This allows Shenandoah GC to handle cleanup efficiently without impacting pause times.

By following these best practices, you can minimize the impact of finalization on the performance of your application when using Shenandoah GC as the garbage collector.

#shenandoah #garbagecollector