JavaScript:SpiderMonkey:GC Futures

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JS GC Futures

Tracking bug is bug 505308

Brain-dump of work items:

  • Speed up allocator
    • remove or mitigate locking ????
    • Use one single GC heap chunk, avoiding frequent mmap and malloc calls bug 506174
  • Speed up collector
    • Allocate short-enough strings from GC heap, not malloc heap bug 402614
    • Allocate object dslots from GC heap, not malloc heap? Alternative: [bug NNNNNN]
    • Based on Gregor's stats consider making 32-byte and 64-byte JSObjects to cover most cases except large objects without any dslots bug 508357
  • Remove byte flag per thing design [bug NNNNNN]
    • Bad cache effects of flags and things allocated from opposite ends of same arena
    • Don't want generality of different thing-types allocated from same size class
      • Can put finalizer or other index/info in the pool, not in each flag's low bits [bug NNNNNN]
      • Compress flags to mark bit in bitmap? [bug NNNNNN]
  • Add new JNI-like (handles, "clothed" not "naked") global rooting API
    • But use C++ to best effect (auto storage class RAII helpers, templates)
    • Make old JS global rooting API be #ifdef JS_NAKED_GC_ROOTS (enabled at first) [bug NNNNNN]
    • Convert mozilla-central to use new global rooting API [bug NNNNNN]
    • Disable JS_NAKED_GC_ROOTS [bug NNNNNN]
  • What about local roots? [bug NNNNNNN]
    • Need write barrier, efficient auto-temp-value rooting [bug NNNNNNN]
    • No naked argv[i] writes [bug NNNNNNN]
    • Conservative stack scanning to avoid temp-value rooting overheads? [bug NNNNNNN]
      • Andreas and Brendan think this is likely best (safety, clean code)
      • Equivalent to well-used (i.e. seldom-used) pinning API in effect but contained:
        • GC from shallow stack
        • clear event loop locals that might entrain garbage
      • 8/4/2009 NEEDS PROMPT INVESTIGATION
  • GC safety static analysis
  • Write barrier for all code including JITted code
  • Write barrier in API
    • write barriers may make natives slower
  • Make GC heap per thread (in JSThreadData)
    • New API for making MT-accessible objects
    • Objects are ST-accessible only without new API usage
    • Safest course for API: #ifdef JS_AUTO_MT_OBJECTS for existing API, new API entry points (C++ API, rather) for new ST vs. MT create-object methods [bug NNNNNNN]
    • Switch mozilla-central code over, turn off JS_AUTO_MT_OBJECTS [bug NNNNNNN]
  • Fast generational copying allocation and collection [bug NNNNNNN]
  • Go to beach
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