From 81e69b85c8bcd9ab8da04c01bc30aaea129b7ff9 Mon Sep 17 00:00:00 2001
From: Uko Kokņevičs
Date: Sun, 19 Oct 2025 10:12:04 +0300
Subject: Make the R/W locks somewhat more fair

---
 test/rw-lock.lisp | 26 ++++++++++++++++++++++++--
 1 file changed, 24 insertions(+), 2 deletions(-)

(limited to 'test')

diff --git a/test/rw-lock.lisp b/test/rw-lock.lisp
index fdb60bd..834d0fd 100644
--- a/test/rw-lock.lisp
+++ b/test/rw-lock.lisp
@@ -2,8 +2,8 @@
 ;; SPDX-FileCopyrightText: 2025 Uko Kokņevičs <perkontevs@gmail.com>
 (defpackage :ukkoclot/test/rw-lock
   (:documentation "Test-suite for :ukkoclot/src/rw-lock.")
-  (:use :c2cl :fiveam :ukkoclot/src/rw-lock)
-  (:import-from :bt2 :with-timeout))
+  (:use :c2cl :fiveam :iterate :ukkoclot/src/rw-lock)
+  (:import-from :bt2 :join-thread :make-thread :with-timeout))
 (in-package :ukkoclot/test/rw-lock)
 
 (def-suite :ukkoclot/rw-lock)
@@ -69,6 +69,28 @@
     (is-false (acquire-read-lock lock :wait nil))
     (is (rw-lock-p (release-write-lock lock)))))
 
+(test read&write-locks.contention
+  (let ((lock (make-rw-lock))
+        (value 0)
+        reader-threads
+        writer-threads)
+    (flet ((reader-fn () (with-read-lock (lock)
+                           (sleep (random 0.1))
+                           value))
+           (writer-fn () (with-write-lock (lock)
+                           (incf value)
+                           (sleep (random 0.1))
+                           (incf value))))
+      (iter (repeat 100)
+            (push (make-thread #'reader-fn) reader-threads)
+            (sleep (random 0.02))
+            (push (make-thread #'writer-fn) writer-threads)))
+    (iter (for writer-thread in writer-threads)
+          (join-thread writer-thread))
+    (is (every #'evenp
+         (iter (for reader-thread in reader-threads)
+               (collect (join-thread reader-thread)))))))
+
 (test with-read-lock.simple
   (let ((lock (make-rw-lock)))
     (with-read-lock (lock)
-- 
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