From: "jeremyevans0 (Jeremy Evans) via ruby-core" Date: 2025-12-02T22:03:21+00:00 Subject: [ruby-core:123989] [Ruby Feature#21721] Allow `Queue` and `SizedQueue` to be used as LIFO queues Issue #21721 has been updated by jeremyevans0 (Jeremy Evans). Eregon (Benoit Daloze) wrote in #note-10: > FWIW it sounds quite bad contention-wise to use a global queue/stack (EDIT: and a stack is worse than a queue re contention) for connections, at least for the case `#connections >= #threads`. > For that case it should be possible to save the connection in a Thread local or so, no? You only need to access the stack/queue when checking a connection in or out of the pool, you don't need to access the stack/queue when you've already checked out a connection. You can store the connection in a Thread/Fiber local while it is checked out. Sequel uses a Thread/Fiber-keyed hash to avoid polluting Thread/Fiber local state. ---------------------------------------- Feature #21721: Allow `Queue` and `SizedQueue` to be used as LIFO queues https://bugs.ruby-lang.org/issues/21721#change-115417 * Author: byroot (Jean Boussier) * Status: Open ---------------------------------------- ### Context Since `Queue` and `SizedQueue` gained a proper timeout mechanism, I've been wanting to use them to implement simpler and more efficient connection pools. However for connection pools you ideally want a LIFO queue because it's preferable to checkout the most recently used connection. ### Problem Both `Queue` and `SizedQueue` only support FIFO because you can only enqueue elements at the beginning of the backing array, and only dequeue at the end. `Queue#push` (aliased as `Queue#<<` and `Queue#enq`) calls `Array#unshift` on the backing array and `Queue#pop` (aliased as `Queue#deq` and `Queue#shift`) calls `Array#pop`. Hence it is impossible to use these two classes for anything other than FIFO queues. I tried to use `git blame` to see if there was a justification for this, but I ended up in a git blame loop around May 2000 https://github.com/ruby/ruby/commit/9da4f78db46764be6dae5e7e83ff48cbecb3fb23 ### Feature I'd like to introduce either of two new methods (or both) to allow for LIFO: - A method to dequeue from the beginning of the backing array (`array_shift`). - A method to enqueue from the end of the backing array (`array_push`). A difficulty I have however is that since the common `shift/pop/push` terms are already used with uncommon meaning, it's hard to come up with good names. Ideas welcome. ### Possible alternatives - Define different classes for LIFO queues - But I find that less flexible, and it means exposing new constant names in the global namespace. - Add an initializer argument to define the queue ordering, e.g. `Queue.new([], lifo: true)` - Similarly, I find this less flexible than to decide the order during enqueue/dequeue - Add an argument to `Queue#pop` and `Queue#push`, e.g. `queue.push(element, front: true)`. -- https://bugs.ruby-lang.org/ ______________________________________________ ruby-core mailing list -- ruby-core@ml.ruby-lang.org To unsubscribe send an email to ruby-core-leave@ml.ruby-lang.org ruby-core info -- https://ml.ruby-lang.org/mailman3/lists/ruby-core.ml.ruby-lang.org/