The Shenandoah garbage collector (GC) is a low-pause garbage collector designed to reduce pause times in large heap applications. One of the key features of Shenandoah GC is its ability to perform concurrent string table scanning and concurrent code root tracing, which significantly improves the performance and responsiveness of garbage collection.
String Table Scanning
The string table is a data structure used by the JVM to store interned strings. Interned strings are strings that share the same content and memory location to reduce memory footprint. The Shenandoah GC performs concurrent string table scanning, which means it scans and processes interned strings concurrently with the application’s execution.
During the string table scanning phase, Shenandoah GC identifies and collects unused interned strings, freeing up memory occupied by these unused strings. By performing this operation concurrently, the GC minimizes the impact on application performance and reduces pause times.
Code Root Tracing
Code roots are locations in the application’s code where references to objects can be found. These code roots need to be traced by the GC to identify live objects and mark them for retention. In the case of Shenandoah GC, code root tracing is done concurrently with the application’s execution.
Concurrent code root tracing allows the GC to trace code roots while the application is still running, reducing pause times and improving the responsiveness of the application. This enables the GC to keep up with the rapid changes in the execution stack and accurately identify live objects.
Benefits of Concurrent String Table Scanning and Code Root Tracing
The concurrent execution of string table scanning and code root tracing in Shenandoah GC offers several benefits, including:
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Reduced pause times: By performing these operations concurrently, Shenandoah GC minimizes the impact on application responsiveness and significantly reduces pause times.
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Improved application performance: With concurrent scanning and tracing, the GC can free up memory occupied by unused interned strings and accurately identify live objects, resulting in improved application performance.
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Enhanced garbage collection efficiency: Concurrent execution of these operations allows the GC to keep up with the application’s execution stack, ensuring accurate identification of live objects and more efficient garbage collection.
In conclusion, the concurrent string table scanning and concurrent code root tracing in Shenandoah GC are essential features that contribute to its low-pause garbage collection capabilities. By performing these operations concurrently with the application’s execution, Shenandoah GC significantly reduces pause times, improves application performance, and enhances garbage collection efficiency.