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- require "delegate"
- # WeakRef is a class to represent a reference to an object that is not seen by
- # the tracing phase of the garbage collector. This allows the referenced
- # object to be garbage collected as if nothing is referring to it. Because
- # WeakRef delegates method calls to the referenced object, it may be used in
- # place of that object, i.e. it is of the same duck type.
- #
- # Usage:
- #
- # foo = Object.new
- # foo = Object.new
- # p foo.to_s # original's class
- # foo = WeakRef.new(foo)
- # p foo.to_s # should be same class
- # ObjectSpace.garbage_collect
- # p foo.to_s # should raise exception (recycled)
- class WeakRef<Delegator
- # RefError is raised if an object cannot be referenced by a WeakRef.
- class RefError<StandardError
- end
- @@id_map = {} # obj -> [ref,...]
- @@id_rev_map = {} # ref -> obj
- @@final = lambda{|id|
- __old_status = Thread.critical
- Thread.critical = true
- begin
- rids = @@id_map[id]
- if rids
- for rid in rids
- @@id_rev_map.delete(rid)
- end
- @@id_map.delete(id)
- end
- rid = @@id_rev_map[id]
- if rid
- @@id_rev_map.delete(id)
- @@id_map[rid].delete(id)
- @@id_map.delete(rid) if @@id_map[rid].empty?
- end
- ensure
- Thread.critical = __old_status
- end
- }
- # Create a new WeakRef from +orig+.
- def initialize(orig)
- super
- __setobj__(orig)
- end
- # Return the object this WeakRef references. Raises RefError if the object
- # has been garbage collected. The object returned is the object to which
- # method calls are delegated (see Delegator).
- def __getobj__
- unless @@id_rev_map[self.__id__] == @__id
- raise RefError, "Illegal Reference - probably recycled", caller(2)
- end
- begin
- ObjectSpace._id2ref(@__id)
- rescue RangeError
- raise RefError, "Illegal Reference - probably recycled", caller(2)
- end
- end
- def __setobj__(obj)
- @__id = obj.__id__
- __old_status = Thread.critical
- begin
- Thread.critical = true
- unless @@id_rev_map.key?(self)
- ObjectSpace.define_finalizer obj, @@final
- ObjectSpace.define_finalizer self, @@final
- end
- @@id_map[@__id] = [] unless @@id_map[@__id]
- ensure
- Thread.critical = __old_status
- end
- @@id_map[@__id].push self.__id__
- @@id_rev_map[self.__id__] = @__id
- end
- # Returns true if the referenced object still exists, and false if it has
- # been garbage collected.
- def weakref_alive?
- @@id_rev_map[self.__id__] == @__id
- end
- end
- if __FILE__ == $0
- require 'thread'
- foo = Object.new
- p foo.to_s # original's class
- foo = WeakRef.new(foo)
- p foo.to_s # should be same class
- ObjectSpace.garbage_collect
- p foo.to_s # should raise exception (recycled)
- end
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