lib/weakref.rb

   1 # Weak Reference class that does not bother GCing.
   2 #
   3 # Usage:
   4 #   foo = Object.new
   5 #   foo = Object.new
   6 #   p foo.to_s                  # original's class
   7 #   foo = WeakRef.new(foo)
   8 #   p foo.to_s                  # should be same class
   9 #   ObjectSpace.garbage_collect
  10 #   p foo.to_s                  # should raise exception (recycled)
  11
  12 require "delegate"
  13 require 'thread'
  14
  15 class WeakRef < Delegator
  16
  17   class RefError < StandardError
  18   end
  19
  20   @@id_map =  {}                # obj -> [ref,...]
  21   @@id_rev_map =  {}            # ref -> obj
  22   @@mutex = Mutex.new
  23   @@final = lambda {|id|
  24     @@mutex.synchronize {
  25       rids = @@id_map[id]
  26       if rids
  27         for rid in rids
  28           @@id_rev_map.delete(rid)
  29         end
  30         @@id_map.delete(id)
  31       end
  32       rid = @@id_rev_map[id]
  33       if rid
  34         @@id_rev_map.delete(id)
  35         @@id_map[rid].delete(id)
  36         @@id_map.delete(rid) if @@id_map[rid].empty?
  37       end
  38     }
  39   }
  40
  41   def initialize(orig)
  42     @__id = orig.object_id
  43     ObjectSpace.define_finalizer orig, @@final
  44     ObjectSpace.define_finalizer self, @@final
  45     @@mutex.synchronize {
  46       @@id_map[@__id] = [] unless @@id_map[@__id]
  47     }
  48     @@id_map[@__id].push self.object_id
  49     @@id_rev_map[self.object_id] = @__id
  50     super
  51   end
  52
  53   def __getobj__
  54     unless @@id_rev_map[self.object_id] == @__id
  55       Kernel::raise RefError, "Invalid Reference - probably recycled", Kernel::caller(2)
  56     end
  57     begin
  58       ObjectSpace._id2ref(@__id)
  59     rescue RangeError
  60       Kernel::raise RefError, "Invalid Reference - probably recycled", Kernel::caller(2)
  61     end
  62   end
  63   def __setobj__(obj)
  64   end
  65
  66   def weakref_alive?
  67     @@id_rev_map[self.object_id] == @__id
  68   end
  69 end
  70
  71 if __FILE__ == $0
  72 #  require 'thread'
  73   foo = Object.new
  74   p foo.to_s                    # original's class
  75   foo = WeakRef.new(foo)
  76   p foo.to_s                    # should be same class
  77   ObjectSpace.garbage_collect
  78   ObjectSpace.garbage_collect
  79   p foo.to_s                    # should raise exception (recycled)
  80 end