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Enhanced JEP 376: ZGC on macOS

By / 28 April 2025 / 4 minutes of reading

JEP 376: ZGC on macOS introduces the support for the Z Garbage Collector (ZGC) on macOS in Java 17, marking a significant milestone in the evolution of the ZGC as a low-latency garbage collector. Prior to this enhancement, ZGC was available on Linux platforms but not on macOS, limiting its use for macOS users. With this update, Java developers working on macOS can now take advantage of ZGC’s capabilities for low-latency garbage collection in high-performance applications.

What is ZGC?

The Z Garbage Collector (ZGC) is a scalable, low-latency garbage collector introduced in Java 11. Unlike traditional garbage collectors, which pause the application for varying amounts of time, ZGC is designed to minimize pause times to an extremely low level (often in the order of a few milliseconds), regardless of the heap size.

ZGC achieves low-latency through techniques like concurrent marking, concurrent relocation of live objects, and no global stop-the-world phases. These capabilities make ZGC an excellent choice for applications that require low-latency operations, such as large-scale data processing, real-time systems, or interactive applications.

Why Support for ZGC on macOS?

Previously, ZGC was available only on Linux and Windows platforms, which meant that developers building on macOS did not have access to this advanced garbage collection option. By adding macOS support, JEP 376 extends the ability to use ZGC to a wider range of environments, especially for developers who use macOS for their development work.

Here are some key reasons why this enhancement is significant:

  1. Cross-Platform Consistency:

    • Developers working across different platforms can now leverage ZGC for consistent behavior in low-latency garbage collection across Linux, Windows, and macOS. This brings more uniformity to performance optimization across various platforms.

  2. Better Support for macOS Users:

    • Many Java developers, especially in the enterprise and research domains, use macOS for their primary development environment. Adding support for ZGC makes it easier for these developers to incorporate low-latency garbage collection without needing to switch to Linux or another platform.

  3. Enhanced Performance for Real-Time Applications:

    • Many macOS users, especially in industries like media, gaming, and high-performance computing, need applications with minimal garbage collection pauses. The addition of ZGC support helps cater to these real-time requirements without compromising on application performance.

  4. Java Performance Optimization:

    • Java’s ZGC aims to handle even large heaps with minimal pause times, making it ideal for applications with significant memory demands. With macOS support, Java developers can optimize the performance of large-scale, memory-intensive applications in their macOS environments.

Key Features of ZGC

The ZGC brings several features to Java, particularly for those requiring low-latency garbage collection:

  • Low Pause Times: ZGC is optimized for minimal pause times, making it suitable for applications that require constant responsiveness.

  • Scalable to Large Heaps: ZGC can handle very large heaps (up to multiple terabytes), ensuring it can support memory-intensive applications without causing long pause times.

  • Concurrent Phases: ZGC operates in concurrent phases for the majority of its work (such as marking and relocation), ensuring that the application thread is not stopped for significant periods.

  • Parallelism: ZGC takes advantage of multi-core processors to perform tasks in parallel, optimizing both time and space during the garbage collection process.

Enabling ZGC on macOS in Java 17

With the introduction of ZGC on macOS, developers can now activate the garbage collector with the -XX:+UseZGC JVM flag on macOS systems. This is how you can enable ZGC on a macOS machine running Java 17 or later:

  1. Running ZGC in a Java application: Simply add the following JVM flag to your command when running your Java application:

java -XX:+UseZGC -jar your-application.jarCode language: CSS (css)

 2.   Example Command for macOS: If you are running a Java application and wish to enable ZGC explicitly on macOS,

       you would use:

java -XX:+UseZGC -Xmx4g -jar myApp.jarCode language: CSS (css)

  1. In this command:

    • -XX:+UseZGC enables ZGC as the garbage collector.

    • -Xmx4g sets the maximum heap size to 4GB for the application.

Benefits of ZGC on macOS

  1. Low Latency: The primary advantage is low-latency garbage collection, which allows applications to run with minimal interruptions for memory management. This is particularly beneficial for applications that require consistent and predictable response times, such as real-time systems or interactive applications.

  2. Large Heap Support: ZGC’s ability to handle very large heaps without significant pauses ensures that macOS users can now handle memory-intensive applications, like large-scale data processing and simulations, efficiently.

  3. Cross-Platform Performance: By enabling ZGC on macOS, developers can achieve a more consistent performance profile across different platforms (Linux, macOS, and Windows), which is valuable for cross-platform development and deployment.

  4. Simplified Garbage Collection Management: ZGC’s concurrent design means that developers can focus on building their applications without needing to deeply tune garbage collection, offering a more hands-off approach to memory management.

Conclusion

JEP 376: ZGC on macOS significantly enhances the garbage collection capabilities available to Java developers, offering support for ZGC on macOS starting with Java 17. This addition allows developers working on macOS to utilize low-latency garbage collection, optimize memory management for large heaps, and take advantage of a more consistent performance profile across platforms.

With this improvement, Java continues to evolve as a robust choice for high-performance applications, offering greater flexibility for developers across various operating systems and use cases. Whether you’re working on real-time applications, large-scale memory management, or cross-platform projects, ZGC on macOS brings substantial benefits to Java’s ecosystem.

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