Project Lilliput would shrink Java object header

Java could get a scaled-down item header, consequently bettering memory use, underneath a proposal becoming floated in the OpenJDK open up resource Java local community this 7 days. Recognised as Challenge Lilliput and led by Red Hat’s Roman Kennke, the work would check out techniques to shrink the item header, with a objective of decreasing it to 64 bits.

At present Java objects have a 128-little bit item header in the 64-little bit HotSpot VM, with a 64-little bit multipurpose header phrase and a 64-little bit class pointer. With common item sizes of 5 to six text, the present item header measurement is substantial, the proposal states. Lowering header measurement would considerably lessen memory tension, decreasing total CPU and memory use for all Java workloads, no matter whether in a substantial in-memory database or a tiny containerized application.

Distinct rewards cited for Challenge Lilliput contain:

  • Decreased heap use.
  • Bigger item allocation fee.
  • Decreased rubbish selection action.
  • Tighter packing of objects.

Other objectives contain generating the header format extra versatile and letting some build or even runtime configuration of how bits are employed. As a secondary objective, it may be achievable to lessen the item header to 32 bits. The proposal states that the item header has been employed (and overloaded) for this kind of purposes as indicating the locking state of an item, tracking the age of each item in rubbish selection, storing id hash code, and type information.

The proposal cites a selection of approaches to check out for allocating and downsizing header fields, this kind of as compressing pointers and backfilling fields regarded at compile time. There are constraints, however, this kind of as necessitating a transform in assembly throughout supported platforms. There also may well be problems with other Java projects, this kind of as Panama, for bridging between Java and C/C++ Loom, supposed to minimize complexity in concurrent apps and Leyden, to address Java problems this kind of as sluggish startup time.

The rapid objective of the initial function program for Lilliput is to brainstorm, obtain thoughts, and devise a evidence of strategy as promptly as achievable.

Copyright © 2021 IDG Communications, Inc.

Maria J. Danford

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