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* gc.c (wmap_each_i): add ObjectSpace::WeakMap#key? method. * lib/weakref.rb (WeakRef#weakref_alive): use above method. git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@43351 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
117 lines
3.2 KiB
Ruby
117 lines
3.2 KiB
Ruby
require "delegate"
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# Weak Reference class that allows a referenced object to be
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# garbage-collected.
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#
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# A WeakRef may be used exactly like the object it references.
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#
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# Usage:
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#
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# foo = Object.new # create a new object instance
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# p foo.to_s # original's class
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# foo = WeakRef.new(foo) # reassign foo with WeakRef instance
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# p foo.to_s # should be same class
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# GC.start # start the garbage collector
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# p foo.to_s # should raise exception (recycled)
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#
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# == Example
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#
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# With help from WeakRef, we can implement our own redimentary WeakHash class.
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#
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# We will call it WeakHash, since it's really just a Hash except all of it's
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# keys and values can be garbage collected.
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#
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# require 'weakref'
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#
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# class WeakHash < Hash
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# def []= key, obj
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# super WeakRef.new(key), WeakRef.new(obj)
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# end
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# end
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#
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# This is just a simple implementation, we've opened the Hash class and changed
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# Hash#store to create a new WeakRef object with +key+ and +obj+ parameters
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# before passing them as our key-value pair to the hash.
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#
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# With this you will have to limit your self to String key's, otherwise you
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# will get an ArgumentError because WeakRef cannot create a finalizer for a
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# Symbol. Symbols are immutable and cannot be garbage collected.
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#
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# Let's see it in action:
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#
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# omg = "lol"
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# c = WeakHash.new
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# c['foo'] = "bar"
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# c['baz'] = Object.new
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# c['qux'] = omg
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# puts c.inspect
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# #=> {"foo"=>"bar", "baz"=>#<Object:0x007f4ddfc6cb48>, "qux"=>"lol"}
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#
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# # Now run the garbage collector
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# GC.start
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# c['foo'] #=> nil
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# c['baz'] #=> nil
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# c['qux'] #=> nil
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# omg #=> "lol"
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#
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# puts c.inspect
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# #=> WeakRef::RefError: Invalid Reference - probably recycled
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#
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# You can see the local variable +omg+ stayed, although it's reference in our
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# hash object was garbage collected, along with the rest of the keys and
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# values. Also, when we tried to inspect our hash, we got a WeakRef::RefError,
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# this is because these objects were also garbage collected.
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class WeakRef < Delegator
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##
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# RefError is raised when a referenced object has been recycled by the
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# garbage collector
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class RefError < StandardError
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end
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@@__map = ::ObjectSpace::WeakMap.new
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##
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# Creates a weak reference to +orig+
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#
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# Raises an ArgumentError if the given +orig+ is immutable, such as Symbol,
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# Fixnum, or Float.
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def initialize(orig)
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case orig
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when true, false, nil
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@delegate_sd_obj = orig
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else
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@@__map[self] = orig
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end
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super
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end
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def __getobj__ # :nodoc:
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@@__map[self] or defined?(@delegate_sd_obj) ? @delegate_sd_obj :
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Kernel::raise(RefError, "Invalid Reference - probably recycled", Kernel::caller(2))
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end
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def __setobj__(obj) # :nodoc:
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end
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##
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# Returns true if the referenced object is still alive.
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def weakref_alive?
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@@__map.key?(self) or defined?(@delegate_sd_obj)
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end
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end
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if __FILE__ == $0
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# require 'thread'
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foo = Object.new
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p foo.to_s # original's class
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foo = WeakRef.new(foo)
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p foo.to_s # should be same class
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ObjectSpace.garbage_collect
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ObjectSpace.garbage_collect
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p foo.to_s # should raise exception (recycled)
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end
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