The Shenandoah Garbage Collector (GC) is a low-pause concurrent GC algorithm developed by the OpenJDK community. It aims to minimize garbage collection pauses and improve overall application responsiveness. In this blog post, we will delve into the inner workings of the Shenandoah GC.
Table of Contents
- Introduction to Garbage Collection
- Shenandoah GC Overview
- Phases of Shenandoah GC
- Benefits of Shenandoah GC
- Conclusion
- Further Reading
Introduction to Garbage Collection
Garbage collection is a fundamental process in managed languages like Java, where the runtime environment automatically reclaims memory from objects that are no longer in use. Traditional garbage collectors have stop-the-world pauses, which can cause significant interruptions in application execution.
Shenandoah GC Overview
Shenandoah GC is designed to minimize pause times by performing garbage collection concurrently with the application threads. It divides heap regions into multiple epochs, where each epoch has a corresponding set of garbage collection phases.
Phases of Shenandoah GC
Initial Mark Phase
During the initial mark phase, the garbage collector pauses application threads to identify the objects directly reachable from roots, such as thread stacks and static variables. This phase is the only stop-the-world phase in Shenandoah GC and has a short pause duration.
Concurrent Mark Phase
The concurrent mark phase is where the majority of the garbage collection work happens concurrently with the application threads. It traverses the object graph and identifies reachable objects. To track changes during this phase, Shenandoah GC uses a snapshot-at-the-beginning (SATB) technique.
Final Mark Phase
Once the application threads finish the concurrent mark phase, the garbage collector performs a final mark phase to capture any objects that became reachable after the concurrent marking started. This phase is also performed concurrently, ensuring minimal pause times.
Benefits of Shenandoah GC
The Shenandoah GC offers several benefits, including:
- Low pause times: By performing most garbage collection work concurrently, Shenandoah GC reduces pause times and improves application responsiveness.
- Scalability: The algorithm is designed to handle heaps of any size, making it suitable for large-scale applications.
- Good throughput: Shenandoah GC maintains good throughput by overlapping garbage collection work with application execution whenever possible.
Conclusion
The Shenandoah Garbage Collector provides a low-pause concurrent garbage collection algorithm that helps reduce pause times and improve application performance. By performing most of the garbage collection work concurrently with application threads, Shenandoah GC enhances the responsiveness of Java applications.