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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