Service refresh 6

New hardware and operating system support

This release supports IBM® z15® hardware, and the following operating systems:

• Red Hat® Enterprise Linux® 7.7
• SUSE Linux Enterprise Server 15 SP1
• z/OS® 2.4

New shared classes cache suboptions for layered caches (64-bit only)

The following new suboptions are available for creating layered caches, where a cache builds on another cache with the same name. You can use these suboptions to save space when you build a Docker container, for example.

• createLayer
• layer=<number> (see this section for general information about layered caches)
• printTopLayerStats
• destroyAllLayers

New shared classes cache suboption to skip disk space checking

When the OpenJ9 VM creates a persistent shared classes cache, it checks that there is sufficient disk space available on the file system. For file systems that do not support the checking of free space, you can set the -Xshareclasses:noPersistentDiskSpaceCheck option, which causes the VM to skip the space checking operation. If there isn't enough disk space available when the cache is written, a SIGBUS or SIGSEGV signal occurs and the VM ends. For more information, see the -Xshareclasses:noPersistentDiskSpaceCheck option.

Option to share 'Unsafe' classes

Classes that are created by using the Unsafe.defineClass class are now stored by default in the shared classes cache. You can use the -XX:-ShareUnsafeClasses option to change the default behavior. For more information, see -XX:[+|-]ShareUnsafeClasses.

Option to record class relationships in the verifier

You can use the new command line option -XX:+ClassRelationshipVerifier to record class relationships in the verifier, which avoids unnecessary class loading and reduces VM startup time. This change is a new approach to bytecode verification that delays the validation of the relationships between classes until the classes must be loaded to run a program, thus loading only those classes that are required. For more information, see -XX:[+|-]ClassRelationshipVerifier.

New operating system support

This release supports the following operating systems:

• Red Hat Enterprise Linux 7.8 and 8.2
• Ubuntu 20.04 LTS

Signal handling implementation change

The IBM signal handling implementation is replaced in this release with the OpenJDK implementation. As a result, the -Dcom.ibm.signalhandling.ignoreLogoff system property command-line option is now ignored. For more information, see Miscellaneous system property command-line options.

Removal of support for Windows 8.1

Due to removal of support for this operating system in the OpenJ9 project, support is also removed in the SDK.

Change to JNI compiler level for Windows

The level of Microsoft Visual Studio compiler that is supported for compiling JNI applications on the Windows operating system has changed from 2010 to 2017. For more information about compiler support, see Supported compilers.

Eclipse API documentation moved

API documentation that applies to Eclipse OpenJ9 is now in the OpenJ9 user documentation rather than the SDK user guide.

Improved processor feature diagnostic information in Java™ dump files

The ENVINFO section of a Java dump file now includes further information about processor features. This information helps to diagnose problems associated with JIT and AOT compilations that depend on underlying hardware.

Updated operating system support

• Support is added for Red Hat Enterprise Linux 8.3.
• Support is removed for Ubuntu 16.04, which is now in extended security maintenance mode.

For a list of supported hardware and operating systems, see Supported environments

Use the -xgcmaxthreads option with the -XX:+AdaptiveGCThreading option to specify a thread count limit.

Using 31-bit native C or C++ code with the 64-bit Java VM on z/OS

This release uses new function in z/OS to simplify the migration of Java applications that use native C or C++ code from the 31-bit SDK to the 64-bit SDK. The 64-bit SDK now has expanded Invocation and Java Native Interface APIs to allow 31-bit native code to compile, link, and interoperate with the 64-bit SDK. This feature requires APAR PH28966 on z/OS 2.3 or later. For more information, see Using 31-bit native code with the 64-bit Java VM (z/OS only).

Updated platform system support

• Support is added for Red Hat Enterprise Linux 8.4.

For a list of supported hardware and operating systems, see Supported environments