From: ts <decoux@...>
Date: 2004-07-31T19:32:40+09:00
Subject: Re: C ext: GC claiming objects early

>>>>> "T" == Tilman Sauerbeck <tilman@code-monkey.de> writes:

T> Yeah. Although if I make the parent object (the XmmsClient, 'o') know
T> about (and mark) the Result objects, I've got a circular reference,
T> since the result objects mark their parent, which is 'o'.

 Circular reference is not a problem because the GC is a mark-sweep GC.

 bdb use circular reference and it work fine.

 For example (this is cats.rb)

   def tt
      bdb = BDB::Btree.open "tmp/aa", nil, "w", "marshal" => true
      aux = BDB::Btree.open "tmp/bb", nil, "w", 
         "set_flags" => BDB::DUPSORT, "marshal" => true
      bdb.associate(aux) { |aux1, key, value| value.life }
      nil
   end

   tt
   GC.start


 `bdb' will mark `aux' and `aux' will mark `bdb'

 When the GC run, it will not mark `bdb' because it has no reference to it,
 and it will not mark `aux' for the same reason. At the sweep phase, `bdb'
 and `aux' are removed (closed in this case)

 Now with

   def tt
      bdb = BDB::Btree.open "tmp/aa", nil, "w", "marshal" => true
      aux = BDB::Btree.open "tmp/bb", nil, "w", 
         "set_flags" => BDB::DUPSORT, "marshal" => true
      bdb.associate(aux) { |aux1, key, value| value.life }
      bdb
   end

   a = tt
   GC.start

 the GC will mark `a' (i.e. `bdb') which mark `aux' (same if it return
 `aux' rather than `bdb') 



Guy Decoux