Sapphire Garbage Collector for Jikes RVM

This repository contains a copy of Jikes RVM patched with an implement of the Sapphire garbage collection algorithm.

This implementation is the result of research and technical work by:

• Laurence Hellyer
• Tomoharu Ugawa (Kochi University of Technology)
• Carl G. Ritson (University of Kent)
• Richard E. Jones (University of Kent)

Please contact Carl Ritson or Richard Jones for more information.

Sapphire is an on-the-fly concurrent copying garbage collector. This means it does not need to stop all user threads to perform garbage collection. Thread stacks are scanned individually. This leading to sub-millisecond pause times during garbage collection.

Sapphire was designed by Richard Hudson and Eliot Moss. It is documented in a journal paper here.

This implementation was performed with permission from Intel who hold patents on Sapphire's design.

The official Jikes RVM website and repository can be found here.

Building

Standard Jikes RVM dependencies apply for building with ant (see here).

To build optimised (adjust host.name appropriately):

ant -Dhost.name=x86_64-osx -Dconfig.name=FastAdaptiveOTFSapphire

To build debug (adjust host.name appropriately):

ant -Dhost.name=x86_64-osx -Dconfig.name=ExtremeAssertionsBaseBaseOTFSapphire

RVM will be in the dist directory.

Run-time Options

The following options can be used to changed Sapphire's run-time behaviour.

ConcurrentCopyMethod

Select the method used for copying concurrent with the mutator, e.g.

-X:gc:concurrentCopyMethod=always-htm2

value	description
cas / cas2	default per-word synchronised methods
unsafe / unsafe2	unsynchronised methods
stm / mstm / stmseq / stmseq2 / stmseq2p / stmseq2n	software transactional
htm / htm2 / mhtm	hardware transactional

All of these options can be prefixed with "always-" to force the method to be used for all collections. Normally stop-the-world collection will default to unsafe2. Methods postfixed with 2 use a more efficient copying order than the same method without the postfix.

ConcurrentCopyTransactionSize

Select the size of transactions for mhtm and mstm concurrent copying methods, e.g.

-X:gc:concurrentCopyTransactionSize=256

ConcurrentTriggerMethod

Select the method used to trigger concurrent collection, i.e. when collection will be started. Interacts with ConcurrentTrigger.

-X:gc:concurrentTriggerMethod=allocation

value	description
allocation	pages allocated since last collection start
OOGCAllocation	pages allocated since last collection end
percentage	percentage of the heap allocated
period	microseconds since last collection start
time	microseconds since last collection end

ConcurrentTrigger

Value used with ConcurrentTriggerMethod may represent pages, time or a percentage.

SapphireSTWPhase

Force one or more Sapphire phases to run stop-the-world, e.g.

-X:gc:SapphireSTWPhase=flip

One or more of the following separated by commas:

• alloc
• copy
• flip
• root