Chapter 3. Major differences between Red Hat build of OpenJDK 11 and Red Hat build of OpenJDK 17

Red Hat build of OpenJDK 17 no longer includes the Concurrent Mark Sweep (CMS) garbage collector, which was commonly used in earlier releases for workloads sensitive to pause times and latency.

If you have been using the CMS collector, switch to one of the following collectors based on your workload before migrating to Red Hat build of OpenJDK 17 or later.

For more information, see JEP 363: Remove the Concurrent Mark Sweep (CMS) Garbage Collector.

Red Hat build of OpenJDK 17 no longer includes any of the following features:

The use of these tools and APIs has been limited since the introduction of the JMOD module format in OpenJDK 9.

For more information, see JEP 367: Remove the Pack200 Tools and API.

Red Hat build of OpenJDK 17 no longer includes any of the following features:

The scripting API, javax.script, is still available in Red Hat build of OpenJDK 17 or later. Similar to releases before OpenJDK 8, you can use the javax.script API with a JavaScript engine of your choice, such as Rhino or the now externally maintained Nashorn JavaScript engine.

For more information, see JEP 372: Remove the Nashorn JavaScript Engine.

Red Hat build of OpenJDK 17 introduces strong encapsulation of all internal elements of the JDK, apart from critical internal APIs such as sun.misc.Unsafe. From Red Hat build of OpenJDK 17 onward, you cannot relax the strong encapsulation of internal elements by using a single command-line option. This means that Red Hat build of OpenJDK 17 and later versions prevent reflective access to JDK internal types apart from critical internal APIs.

For more information, see JEP 403: Strongly Encapsulate JDK Internals.

Red Hat build of OpenJDK 17 disables biased locking by default. In Red Hat build of OpenJDK 17, you can enable biased locking by setting the -XX:+UseBiasedLocking JVM option at startup. However, the -XX:+UseBiasedLocking option is deprecated in Red Hat build of OpenJDK 17 and planned for removal in OpenJDK 18.

For more information, see JEP 374: Deprecate and Disable Biased Locking.

Red Hat build of OpenJDK 17 removes the java.rmi.activation package and its associated rmid activation daemon for Java remote method invocation (RMI). Other RMI features are still available in Red Hat build of OpenJDK 17 and later versions.

For more information, see JEP 407: Remove RMI Activation.

Red Hat build of OpenJDK 17 removes the Graal compiler, which comprises the jaotc tool and the jdk.internal.vm.compiler and jdk.internal.vm.compiler.management modules. From Red Hat build of OpenJDK 17 onward, if you want to use ahead-of-time (AOT) compilation, you can use GraalVM.

For more information, see JEP 410: Remove the Experimental AOT and JIT Compiler.