From a13098494d59fb1e6f8cc980a12f408f58a60727 Mon Sep 17 00:00:00 2001
From: Christopher Baines <mail@cbaines.net>
Date: Mon, 17 Nov 2025 11:18:23 +0000
Subject: [PATCH] Fix a bug where resources pools could empty with waiters

---
 knots/resource-pool.scm |  4 ++++
 tests/resource-pool.scm | 17 +++++++++++++++++
 2 files changed, 21 insertions(+)

diff --git a/knots/resource-pool.scm b/knots/resource-pool.scm
index 232df77..d802260 100644
--- a/knots/resource-pool.scm
+++ b/knots/resource-pool.scm
@@ -939,6 +939,10 @@
                               (eq? x resource))
                             resources)))
 
+           (when (and (not (q-empty? waiters))
+                      (< (- (length resources) 1)
+                         max-size))
+             (spawn-fiber-to-return-new-resource))
 
            (loop (if index
                      (remove-at-index! resources index)
diff --git a/tests/resource-pool.scm b/tests/resource-pool.scm
index 461d04b..3999dde 100644
--- a/tests/resource-pool.scm
+++ b/tests/resource-pool.scm
@@ -211,4 +211,21 @@
 
      (destroy-resource-pool resource-pool))))
 
+(run-fibers-for-tests
+ (lambda ()
+   (let ((resource-pool (make-resource-pool
+                         (const 'foo)
+                         1
+                         #:lifetime 1
+                         #:destructor
+                         (const #t))))
+     (for-each
+      (lambda _
+        (with-resource-from-pool resource-pool
+            res
+          res))
+      (iota 20))
+
+     (destroy-resource-pool resource-pool))))
+
 (display "resource-pool test finished successfully\n")