From: "nobu (Nobuyoshi Nakada)" Date: 2013-12-14T13:33:17+09:00 Subject: [ruby-core:59102] [ruby-trunk - Feature #6309] Add a reference queue for weak references Issue #6309 has been updated by nobu (Nobuyoshi Nakada). My PR: https://github.com/ruby/ruby/pull/480 ---------------------------------------- Feature #6309: Add a reference queue for weak references https://bugs.ruby-lang.org/issues/6309#change-43663 Author: headius (Charles Nutter) Status: Assigned Priority: Normal Assignee: matz (Yukihiro Matsumoto) Category: Target version: current: 2.1.0 Most interesting uses of WeakRef are much harder to do efficiently without a reference queue. A reference queue, as implemented by the JVM, is basically a queue into which weak references are placed some time after the object they refer to has been collected. The queue can be polled cheaply to look for collected references. A simple example of usage can be seen in the weakling gem, with an efficient implementation of an ID hash: https://github.com/headius/weakling/blob/master/lib/weakling/collections.rb Notice the _cleanup method is called for every operation, to keep the hash clear of dead references. Failure to have a _cleanup method would mean the hash grows without bounds. _cleanup cannot be implemented efficiently on MRI at present because there's no reference queue implementation. On MRI, _cleanup would have to perform a linear scan of all stored values periodically to search for dead references. For a heavily used hash with many live values, this becomes a very expensive operation. It's probably possible to implement reference queues efficiently atop the new ObjectSpace::WeakMap internals, since it already keeps track of weak references and can run code when a weak reference no longer refers to a live object. -- http://bugs.ruby-lang.org/