Java developers, rejoice! The latest release, Java 22, introduces a major enhancement to garbage collection with JEP 423: Region Pinning for G1. This new feature addresses a longstanding problem that led to latency spikes during critical sections of code.

What is the problem?

Java applications often engage with unmanaged code, typically written in languages like C or C++. This interaction is facilitated through the Java Native Interface (JNI). However, there's a significant challenge when using the G1 garbage collector, which is the default in Java, particularly during JNI critical regions.

Traditionally, the G1 garbage collector would halt all garbage collection activities whenever a thread entered a critical JNI region. This approach was adopted to ensure data consistency, as it prevents the garbage collector from modifying or moving the data being accessed by the JNI. While effective in maintaining data integrity, this method led to noticeable and often disruptive pauses in the application's performance.

These pauses occur because the garbage collector, in its efforts to manage memory efficiently, must stop its operations entirely during these critical interactions. This halt in activity means that the memory management is paused, leading to potential buildup of unused objects, which then requires more time to clear when the garbage collection resumes. This can significantly affect the performance and responsiveness of Java applications, especially those that frequently interact with unmanaged code.

How does JEP 423 solve this problem?

JEP 423 introduces an innovative technique known as region pinning. This method allows developers to strategically identify and select specific memory regions that contain critical objects within their Java applications. Once these crucial regions are identified, developers can "pin" them, effectively marking them as immovable during the garbage collection processes.

The primary advantage of region pinning is that it enables the Garbage First (G1) garbage collector to execute its cleaning and memory reclaiming tasks on other parts of the heap without disrupting the operation of the pinned regions. This selective garbage collection ensures that critical memory areas remain untouched and fully operational, thereby preventing any performance degradation that might occur due to pausing or halting of memory management in these regions.

Benefits of Region Pinning

• Reduced Latency: By eliminating the need to disable GC entirely, region pinning significantly reduces pauses experienced during critical JNI sections. This leads to a smoother and more responsive user experience.

• Improved Interoperability: Region pinning strengthens Java's ability to work seamlessly with unmanaged code. Developers can leverage JNI functionalities without sacrificing application performance.

• Safer Memory Management: Region pinning doesn't compromise data integrity. Critical objects remain pinned and protected throughout the garbage collection process.

Conclusion

In conclusion, Java 22's introduction of JEP 423 with the Region Pinning feature for the G1 garbage collector marks a significant advancement in Java's capabilities, particularly in handling interactions with unmanaged code. This enhancement not only mitigates the performance issues previously caused by garbage collection pauses but also improves the overall efficiency and reliability of Java applications. By allowing developers to pin critical memory regions, Java 22 ensures that applications remain responsive and performant, even during complex operations involving native interfaces. This update is a testament to Java's ongoing commitment to innovation and its adaptability to the evolving needs of modern software development.

References

• OpenJDK JEP 423: Region Pinning for G1: https://openjdk.java.net/jeps/423