From: "byroot (Jean Boussier) via ruby-core" Date: 2025-12-03T07:18:59+00:00 Subject: [ruby-core:123993] [Ruby Feature#21721] Allow `Queue` and `SizedQueue` to be used as LIFO queues Issue #21721 has been updated by byroot (Jean Boussier). > To get an idea of the gain, how about benchmarking with a Thread::Queue for the AR::ConnectionPool? Here's a benchmark of `Thread::Queue` vs Active Record's stack, vs the `TimedStack` in the popular `connection_pool` gem https://gist.github.com/byroot/2f80381eaac17efe79c5e0274753545d ``` ruby 3.4.6 (2025-09-16 revision dbd83256b1) +YJIT +PRISM [arm64-darwin24] Warming up -------------------------------------- core-queue 1.357M i/100ms ar-queue 559.037k i/100ms cp gem 278.748k i/100ms Calculating ------------------------------------- core-queue 16.361M (� 0.3%) i/s (61.12 ns/i) - 82.796M in 5.060491s ar-queue 6.267M (� 1.7%) i/s (159.57 ns/i) - 31.865M in 5.086122s cp gem 2.952M (� 1.5%) i/s (338.80 ns/i) - 14.774M in 5.006458s Comparison: core-queue: 16361424.8 i/s ar-queue: 6266892.1 i/s - 2.61x slower cp gem: 2951618.2 i/s - 5.54x slower ``` ---------------------------------------- Feature #21721: Allow `Queue` and `SizedQueue` to be used as LIFO queues https://bugs.ruby-lang.org/issues/21721#change-115420 * 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/