RELEASE NOTES: JDK 21.0.3

Align `javac` with the Java Language Specification by Rejecting `final` in Record Patterns

JDK 21 introduced pattern matching in the Java language. However, javac allowed final in front of a record pattern, such as (case final R(...) ->), something which is not allowed by the Java Language Specification.

Programs that could be compiled erroneously in JDK21 with final will now fail to compile. This change fixes the issue in the compiler. Impacted users will need to remove the final keyword.

Update XML Security for Java to 3.0.3

The XML Signature implementation has been updated to Santuario 3.0.3. Support for four new SHA-3 based RSA-MGF1 SignatureMethod algorithms have been added: SignatureMethod.SHA3_224_RSA_MGF1, SignatureMethod.SHA3_256_RSA_MGF1, SignatureMethod.SHA3_384_RSA_MGF1, and SignatureMethod.SHA3_512_RSA_MGF1.

Update XML Security for Java to 3.0.3

The XML Signature implementation has been updated to Santuario 3.0.3. Support for four new SHA-3 based RSA-MGF1 signature methods have been added: SHA3_224_RSA_MGF1, SHA3_256_RSA_MGF1, SHA3_384_RSA_MGF1, and SHA3_512_RSA_MGF1. While these new algorithm URIs are not defined in javax.xml.crypto.dsig.SignatureMethod in the JDK update releases, they may be represented as string literals in order to be functionally equivalent. SHA-3 hash algorithm support was delivered to JDK 9 via JEP 287. Releases earlier than that may use third party security providers.

Make `TrimNativeHeapInterval` a Product Switch

TrimNativeHeapInterval has been made an official product switch. It allows the JVM to trim the native heap at periodic intervals.

This option is only available on Linux with glibc.

AWT SystemTray API Is Not Supported on Most Linux Desktops

The java.awt.SystemTray API is used for notifications in a desktop taskbar and may include an icon representing an application. On Linux, the Gnome desktop's own icon support in the taskbar has not worked properly for several years due to a platform bug. This, in turn, has affected the JDK's API, which relies upon that.

Therefore, in accordance with the existing Java SE specification, java.awt.SystemTray.isSupported() will return false where ever the JDK determines the platform bug is likely to be present.

The impact of this is likely to be limited since applications always must check for that support anyway. Additionally, some distros have not supported the SystemTray for several years unless the end-user chooses to install non-bundled desktop extensions.

Added Certainly R1 and E1 Root Certificates

The following root certificates have been added to the cacerts truststore: ``` + Certainly + certainlyrootr1 DN: CN=Certainly Root R1, O=Certainly, C=US

• Certainly
• certainlyroote1 DN: CN=Certainly Root E1, O=Certainly, C=US ```

JVM May Crash or Malfunction When Using ZGC and Non-Default `ObjectAlignmentInBytes`

Running the JVM with -XX:+UseZGC and non-default value of -XX:ObjectAlignmentInBytes may lead to JVM crashes or incorrect execution.

Parallel: Precise Parallel Scanning of Large Object Arrays for Young Collection Roots

During a young collection, ParallelGC partitions the old generation into 64kB stripes when scanning it for references into the young generation. These stripes are assigned to worker threads that do the scanning in parallel as work units.

Before this change, Parallel GC always scanned these stripes completely even if only a small part had been known to contain interesting references. Additionally, every worker thread processed the objects that start in that stripe by itself, including parts of objects that extend into other stripes. This behavior limited parallelism when processing large objects. A single large object, potentially containing thousands of references, had been scanned by a single thread only and in full. This would cause bad scaling due to memory sharing and cache misses in the subsequent long, work stealing phase.

With this change, Parallel GC workers limit work to their stripe and only process interesting parts of large object arrays. This reduces the work done by a single thread for a stripe, improves parallelism, and reduces the amount of work stealing. Parallel GC pauses are now on par with G1 in presence of large object arrays, reducing pause times by 4-5 times in some cases.

Name Change for Filler Array Objects from `jdk.vm.internal.FillerArray` to `[Ljdk/internal/vm/FillerElement;`

One HotSpot virtual machine internal class to indicate an area of dead (unreachable) memory has been renamed to conform to the Java class naming standard to avoid confusing external applications parsing virtual machine class histograms provided by jmap -histo.

There are applications that parse the output of jmap -histo which fail when encountering the class jdk.vm.internal.FillerArray. In particular, the issue is that this type of filler object represents a flexibly sized range of unreachable memory but is named as if it were a fixed size non-array object. Then, for example, calculating the instance size of these objects from the jmap -histo output can result in non-integral instance sizes, confusing applications.

This problem has been fixed by changing the name of this class to the array-like name [Ljdk/internal/vm/FillerElement;.