From f519c709b387e350cdf3ffc71e31c9fbfbb502e5 Mon Sep 17 00:00:00 2001
From: Uko Kokņevičs
Date: Sun, 19 Oct 2025 07:36:50 +0300
Subject: Added checks against releasing an untaken lock

---
 src/rw-lock.lisp  |  2 ++
 test/rw-lock.lisp | 12 ++++++++++++
 2 files changed, 14 insertions(+)

diff --git a/src/rw-lock.lisp b/src/rw-lock.lisp
index b32d3d0..bd2606c 100644
--- a/src/rw-lock.lisp
+++ b/src/rw-lock.lisp
@@ -72,6 +72,7 @@
   (check-type rw-lock rw-lock)
   (with-slots (lock unlocked readers has-writer) rw-lock
     (with-lock-held (lock)
+      (assert (> readers 0) nil "Trying to release a read lock that's not taken!")
       (decf readers)
       (when (zerop readers)
         (condition-broadcast unlocked))))
@@ -117,6 +118,7 @@
   (check-type rw-lock rw-lock)
   (with-slots (lock unlocked readers has-writer) rw-lock
     (with-lock-held (lock)
+      (assert has-writer nil "Trying to release a write lock that's not taken!")
       (setf has-writer nil)
       (condition-broadcast unlocked)))
   rw-lock)
diff --git a/test/rw-lock.lisp b/test/rw-lock.lisp
index 4460398..fdb60bd 100644
--- a/test/rw-lock.lisp
+++ b/test/rw-lock.lisp
@@ -33,6 +33,12 @@
       (is (rw-lock-p (release-read-lock lock)))
       (is (rw-lock-p (release-read-lock lock))))))
 
+(test release-read-lock.failing
+  (let ((lock (make-rw-lock)))
+    (signals error (release-read-lock lock))
+    (is-true (acquire-write-lock lock :wait nil))
+    (signals error (release-read-lock lock))))
+
 (test acquire-write-lock.no-contention
   (let ((lock (make-rw-lock)))
     (is-true (acquire-write-lock lock :wait nil))
@@ -46,6 +52,12 @@
     (is-false (acquire-write-lock lock :wait nil))
     (is (rw-lock-p (release-write-lock lock)))))
 
+(test acquire-write-lock.failing
+  (let ((lock (make-rw-lock)))
+    (signals error (release-write-lock lock))
+    (is-true (acquire-read-lock lock :wait nil))
+    (signals error (release-write-lock lock))))
+
 (test acquire-read&write-lock.contention
   (let ((lock (make-rw-lock)))
     (is-true (acquire-read-lock lock :wait nil))
-- 
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