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What's new in version 0.49.0

The following new features and notable changes since version 0.48.0 are included in this release:

Features and changes

Binaries and supported environments

Eclipse OpenJ9™ release 0.49.0 supports OpenJDK 8, 11, 17, 21, and 23.

macOS 12 is out of support and is removed from the list of supported platforms.

To learn more about support for OpenJ9 releases, including OpenJDK levels and platform support, see Supported environments.

Change to the shared classes cache generation number

The shared classes cache generation number is incremented. The increment in the shared classes cache generation number causes the VM to create a new shared classes cache, rather than re-creating or reusing an existing cache.

To save space, all existing shared caches can be removed unless they are in use by an earlier release. For more information, see Housekeeping and -Xshareclasses.

The shared classes cache generation number is modified because of a change in the format of ROMClasses that are stored in the shared classes cache. A new flag J9AccClassIsShared is added to ROMClasses to indicate whether a ROMClass was loaded from a shared classes cache or from a VM.

New shared classes cache suboption added to adjust the number of startup hints that can be stored

You can use the -Xshareclasses:extraStartupHints=<number> option to adjust the number of startup hints that can be stored in a shared cache. By default, you can store only up to 64 startup hints in a shared cache.

For more information, see -Xshareclasses:extraStartupHints.

The VM can use compressed references to decrease the size of Java objects and make better use of the available space in the Java heap. You can now control the compressed reference allocation with the following options:

For more information, see Compressed references.

Start of content that applies to Java 11 (LTS) and later New -XX:[+|-]FlightRecorder option added

This release supports, as a technical preview, JDK Flight Recorder (JFR) that is available for OpenJDK 11 and later running on Linux® x86 and Linux on AArch64 only.

You can collect profiling and diagnostic information with JFR. You can enable or disable JFR in the VM with the -XX:[+|-]FlightRecorder option. End of content that applies only to Java 11 and later

Known problems and full release information

To see known problems and a complete list of changes between Eclipse OpenJ9 v0.48.0 and v0.49.0 releases, see the Release notes.