XPCOMGC

XPCOMGC is the Mozilla 2 project to convert the XPCOM object model from reference counting to use MMgc garbage collection.

General Info

TODO: collect/format information from the newsgroup discussion.

Tasks

• Add the request model threadsafety to MMgc bug 395962
• Give MMgc the ability to recognize "inner" pointers to objects as typically used by C++ multiple inheritance bug 388070
• Make the world depend on a common MMgc
• Rewrite XPCOM addref/release handling
  • Remove the cycle collector
  • Use textual search/replace to remove most calls to NS_ADDREF/NS_RELEASE
  • Use automatic finding to identify remaining references for manual cleanup
  • Make all COM objects inherit from GCObject
  • Rewrite nsCOMPtr+friends to be a lightweight wrapper for GC writebarriers
  • Make stack pointers raw pointers
  • Fix some COM-holding utility classes:
    • nsCOMArray
    • hashtables: nsInterfaceHashtable and nsInterfaceHashKey
  • Rewrite XPCOM weakrefs to be GCWeakRefs
    • And remove those that can be regular GC references
• Identify and deal with multi-threading, especially
  • Initialize and suspend requests around blocking activity
  • Analyze code for deadlock possibilities.

Patch Queue

The XPCOMGC work is currently taking place in mercurial patch queues on top of the ActionMonkey repositories:

• http://hg.mozilla.org/users/bsmedberg_mozilla.com/xpcomgc-patches/
• http://hg.mozilla.org/users/bsmedberg_mozilla.com/xpcomgc-tamarin-patches/