mpmc-queue

multiple-producer-multiple-consumer queue for emacs (>= 26.0).

Installation

You can start using this by putting mpmc-queue.el in your load-path.

How to Use

You can create a mpmc queue with mpmc-queue--create function, and can enqueue or dequeue elements by mpmc-queue-put or mpmc-queue-get functions. There is also mpmc-queue-peek function that returns the first element without removing it from the queue:

;; queue creation
(setq-local q (mpmc-queue--create))

;; basic queue operations
(mpmc-queue-put q 1)
(mpmc-queue-peek q) ;; => 1
(mpmc-queue-get q) ;; => 1

(mpmc-queue-empty-p q) ;; => t

;; non-blocking vs. blocking
(mpmc-queue-get q t) ;; => nil
(mpmc-queue-get q) ;; => blocks until an element is available in the queue

mpmc-queue-get and mpmc-queue-peek functions take one optional argument (non-blocking). If this optional argument is t and the queue is empty, these functions return nil immediately. If the argument is nil and the queue is empty, these block until an element is available in the queue.

MPMC Queue Structure

This queue has 3 fields:

• internal-queue: the internal queue defined in queue.el
• mutex: the mutex associated with this queue.
• non-empty-condition: the condition variable used to notify changes from the empty state to a non-empty state.

There is macro mpmc-queue--with-mutex which runs the given body while holding the mutex of a mpmc queue:

(setq-local q (mpmc-queue--create))
(mpmc-queue--with-mutex q
    ;; do whatever you want with the queue
    (...)
    )