In the world of garbage collection (GC) algorithms, the goal is to minimize the pause times and decrease the impact of GC on application performance. Shenandoah GC is one such GC algorithm that focuses on reducing pause times by performing the evacuation and compaction processes concurrently.
Evacuation
Evacuation is the process of moving live objects from one memory region to another during GC. In concurrent evacuation, Shenandoah GC moves objects concurrently with the execution of the application, reducing or even eliminating long GC pause times.
During concurrent evacuation, Shenandoah GC identifies live objects by using concurrent marking. It maintains snapshot-at-beginning (SAB) semantics, ensuring that objects moved during evacuation remain coherent with running threads.
Shenandoah GC uses an incremental update to track the changes made to object references while maintaining coherence. It also employs a write barrier mechanism to redirect object references to new memory locations during the evacuation process.
The concurrent evacuation process in Shenandoah GC ensures a highly concurrent environment for the application to execute, resulting in low pause times.
Compaction
Compaction is the process of reducing memory fragmentation by moving objects closer together, thus making the memory more contiguous. Concurrent compaction in Shenandoah GC is another technique that helps reduce pause times.
During concurrent compaction, Shenandoah GC automatically identifies fragmented memory regions and concurrently compacts them. It moves objects from fragmented memory regions to a compacted memory region, making more memory available for allocation and improving overall memory utilization.
Similarly to concurrent evacuation, concurrent compaction in Shenandoah GC operates concurrently with the application’s execution. It minimizes pause times by reducing the need for stopping the application to compact memory regions.
Benefits
By performing concurrent evacuation and concurrent compaction, Shenandoah GC offers several benefits:
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Reduced pause times: Concurrent execution of evacuation and compaction processes minimizes the duration of GC pauses, allowing the application to continue its execution smoothly.
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Improved application throughput: Lower pause times result in improved application throughput, as less time is spent on garbage collection.
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Better user experience: With reduced pause times, user-facing applications experience fewer hiccups and provide a more responsive and seamless user experience.
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Higher memory efficiency: Concurrent compaction reduces memory fragmentation, allowing for better memory utilization and reduced memory footprint.
Conclusion
Shenandoah GC’s concurrent evacuation and concurrent compaction aim to minimize pause times and improve application performance. By performing these processes concurrently with the application’s execution, Shenandoah GC provides a highly concurrent environment, resulting in reduced pauses, improved throughput, and enhanced user experience.
With its focus on reducing pause times and providing enhanced performance, Shenandoah GC is a compelling choice for applications that require low-latency and high-throughput garbage collection.
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