In recent improvements to the Shenandoah garbage collector (GC), a new feature called Adaptive Direct Forwarding has been introduced. This feature enhances the performance of concurrent compaction by reducing the time taken for object forwarding.

What is Direct Forwarding?

Direct forwarding is a process in the GC where objects are marked and then relocated to a new memory location. This is done to ensure that memory is utilized more efficiently and to avoid fragmentation. Traditionally, during concurrent compaction, objects are forwarded in two steps: first marking the objects and then copying them to a new location.

Introducing Adaptive Direct Forwarding

Adaptive Direct Forwarding tackles the limitation of the standard two-step forwarding by combining both steps into a single atomic operation. By eliminating the need for separate marking and copying phases, this technique significantly reduces the overhead and processing time associated with memory compaction.

In Adaptive Direct Forwarding, the GC threads are instructed to directly copy and mark objects without any intermediate steps. This approach allows objects to be moved to their new positions in a more efficient manner. The overall result is a substantial reduction in the pause times during garbage collection.

Concurrent Compaction Stats in Shenandoah GC

Another significant improvement in the Shenandoah GC is the introduction of concurrent compaction statistics. Concurrent compaction is the process of rearranging live objects in memory to reduce fragmentation and improve memory utilization. While this process occurs concurrently with the application’s execution, it is essential to track its progress and effectiveness.

With the addition of concurrent compaction statistics, developers can now monitor and analyze various metrics related to memory compaction. These metrics include the number of regions compacted, the amount of free memory obtained, the total compaction time, and more. By providing valuable insights into the efficiency of memory compaction, developers can optimize the GC settings and improve application performance.

Conclusion

The introduction of Adaptive Direct Forwarding and concurrent compaction statistics in the Shenandoah GC brings notable advancements to garbage collection in the Java ecosystem. By combining marking and copying into a single atomic operation, Adaptive Direct Forwarding reduces the overhead of concurrent compaction, resulting in improved performance and reduced pause times. Additionally, the availability of concurrent compaction statistics offers developers a valuable tool for monitoring and optimizing memory compaction in their applications.

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