From: "Eregon (Benoit Daloze) via ruby-core" Date: 2025-12-02T21:25:59+00:00 Subject: [ruby-core:123988] [Ruby Feature#21721] Allow `Queue` and `SizedQueue` to be used as LIFO queues Issue #21721 has been updated by Eregon (Benoit Daloze). To get an idea of the gain, how about benchmarking with a Thread::Queue for the AR::ConnectionPool? For the micro benchmark it probably doesn't matter much semantically if LIFO or FIFO I guess since only 1 thread, but that way we can have an idea of the possible gain. FWIW it sounds quite bad contention-wise to use a global queue/stack 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? ---------------------------------------- Feature #21721: Allow `Queue` and `SizedQueue` to be used as LIFO queues https://bugs.ruby-lang.org/issues/21721#change-115416 * 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/