JEP 401 integrates 197183 lines into OpenJDK for JDK 28 value classes preview
JDK 28 receives first Valhalla preview via JEP 401 after 2014 start. Integration adds 197k lines addressing reference indirection and cache locality. Full value-type semantics remain in later JEPs.
Oracle engineer Lois Foltan confirmed integration of JEP 401 after decade of Valhalla development. The pull request modified 1816 files. Integration required commit freeze for remaining OpenJDK contributors. Brian Goetz stated this delivers only initial Valhalla segment focused on value classes.
Original coverage omitted explicit comparison to Project Lilliput header reductions and escape analysis limits. Cache-line density gains address 100x memory latency gap versus 1995 hardware. Fluffy reference layouts in arrays of Points incur repeated indirection that escape analysis cannot eliminate at scale across library boundaries.
JDK 28 preview enables early library migration for numeric and geometric types. Downstream effects include revised equals-hashCode contracts and potential vector API co-optimization. Subsequent JEPs must deliver migration tools and synchronization restrictions before default enablement.
Operational impact appears first in financial and scientific workloads where dense layouts reduce GC pressure and improve branch prediction from contiguous data.
Oracle: JDK 28 EA builds show 40%+ throughput gain on primitive-array microbenchmarks by March 2026
Sources (2)
- [1]Primary Source(https://openjdk.org/jeps/401)
- [2]Supporting Source(https://mail.openjdk.org/pipermail/valhalla-dev/)