Psst! A Sneak Peek at StableValue and SegmentMapper by Per Minborg

StableValue provides deferred immutability - fields can be initialized exactly once, even in multi-threaded environments

Offers performance benefits through constant folding - once initialized, values are treated as constants by the JVM

Includes several variants:

• StableValue for single values
• StableFunction for function results
• StableCollections for collections
• StableSupplier for lazy initialization

SegmentMapper provides efficient memory mapping capabilities:

• Maps flat memory to structured data
• Works with records and custom layouts
• Useful for serialization and FFM (Foreign Function & Memory API)
• Reduces verbose boilerplate code while maintaining performance

Key advantages over traditional approaches:

• Better performance than double-checked locking
• Thread-safe initialization
• No synchronization overhead after initialization
• Composable with other stable values
• Null-safety guarantees

Typical use cases:

• Lazy logging initialization
• Caching computed values
• Singleton implementations
• Component initialization in larger applications
• Binary data serialization

Current status:

• StableValue JEP recently submitted
• Targeting mid-20s Java releases
• Being refined before full release
• Part of ongoing Java performance improvements