In this article, we will explore the concepts of Concurrent Pass 1 and Concurrent Pass 2 in the Shenandoah Garbage Collector (GC). Shenandoah is a low-pause, garbage collector designed to minimize the application’s pause time and improve overall throughput.
Table of Contents
Introduction to Shenandoah GC
Shenandoah GC is a garbage collector introduced by the OpenJDK project. It aims to provide consistently low-pause times for applications regardless of the heap size or live data set size. It achieves this by performing garbage collection concurrently with the application threads.
Concurrent Pass 1
Concurrent Pass 1 is the initial phase of garbage collection in Shenandoah GC. It scans the entire heap and identifies regions that contain live objects. This information is necessary for the subsequent phases of garbage collection.
During Concurrent Pass 1, the application threads continue to execute concurrently, allowing the application to run smoothly without experiencing significant pauses. The garbage collector works in parallel with the application threads, ensuring that the garbage collection process does not impact the application’s performance.
Concurrent Pass 2
Concurrent Pass 2 is the second phase of garbage collection in Shenandoah GC. It follows Concurrent Pass 1 and continues the scanning of objects in the heap. Concurrent Pass 2 is an incremental phase, meaning it doesn’t need to stop the application threads to complete.
During Concurrent Pass 2, the garbage collector focuses on young objects, using the information gathered in the previous phases. It identifies and evacuates live objects from young generation regions, promoting them to older generation regions. This helps in freeing up space in the young generation, thereby reducing the frequency of stop-the-world garbage collection events.
The concurrent nature of Concurrent Pass 2 ensures that the application threads continue to execute while the garbage collector works in the background. This concurrency minimizes the pause time and provides a smoother experience for the users.
Conclusion
The Shenandoah GC’s Concurrent Pass 1 and Concurrent Pass 2 play a crucial role in achieving low-pause garbage collection and improving application performance. These concurrent phases allow the garbage collector to work alongside the application, minimizing the impact on the application’s execution and reducing overall pause times.
By utilizing Concurrent Pass 1 to identify live objects and Concurrent Pass 2 to evacuate and promote objects, Shenandoah GC ensures efficient memory management without introducing significant pauses. This makes it a suitable option for performance-critical applications that require high throughput and low latency. #shenandoahgc #garbagecollector