From 643b014a01adadac0d5062a0ea59b2115d983028 Mon Sep 17 00:00:00 2001
From: sshevchenko <sshevchenko@evolution.com>
Date: Fri, 18 Sep 2026 18:28:17 +0200
Subject: [PATCH] Fix resource leak when take is cancelled

The pooled resource came out of the map via Resource.eval, which leaves a
cancellation point before makeFull registers the finalizer. A cancel landing
there dropped the resource without destroying it or returning it to the pool,
so the permit and the idle count stayed correct while the connection leaked.

Moving the map update into the acquire makes taking the resource and
registering its finalizer atomic.

Fixes #708
---
 .../typelevel/keypool/TakeCancelSpec.scala    | 86 +++++++++++++++++++
 .../scala/org/typelevel/keypool/KeyPool.scala | 19 ++--
 2 files changed, 98 insertions(+), 7 deletions(-)
 create mode 100644 core/.jvm/src/test/scala/org/typelevel/keypool/TakeCancelSpec.scala

diff --git a/core/.jvm/src/test/scala/org/typelevel/keypool/TakeCancelSpec.scala b/core/.jvm/src/test/scala/org/typelevel/keypool/TakeCancelSpec.scala
new file mode 100644
index 00000000..d4117e9e
--- /dev/null
+++ b/core/.jvm/src/test/scala/org/typelevel/keypool/TakeCancelSpec.scala
@@ -0,0 +1,86 @@
+/*
+ * Copyright (c) 2019 Typelevel
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of
+ * this software and associated documentation files (the "Software"), to deal in
+ * the Software without restriction, including without limitation the rights to
+ * use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
+ * the Software, and to permit persons to whom the Software is furnished to do so,
+ * subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+ * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+ * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
+ * IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+ * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+package org.typelevel.keypool
+
+import cats.syntax.all._
+import cats.effect._
+
+import scala.concurrent.duration._
+import munit.CatsEffectSuite
+
+class TakeCancelSpec extends CatsEffectSuite {
+
+  test("Cancelling take does not orphan a pooled resource") {
+    val racers = 64
+    val bursts = 400
+    val sink = new java.util.concurrent.atomic.AtomicLong(0L)
+
+    def spin(n: Int): Unit = {
+      var i = 0
+      var acc = 0L
+      while (i < n) {
+        acc += System.nanoTime()
+        i += 1
+      }
+      sink.set(acc)
+    }
+
+    for {
+      allocated <- Ref[IO].of(0)
+      destroyed <- Ref[IO].of(0)
+      state <- KeyPool
+        .Builder(
+          (_: Unit) => allocated.updateAndGet(_ + 1),
+          (_: Int) => destroyed.update(_ + 1)
+        )
+        .withIdleTimeAllowedInPool(Duration.Inf)
+        .withMaxPerKey(Function.const(racers * 2))
+        .withMaxTotal(racers * 2)
+        .build
+        .use { pool =>
+          val seed = List.fill(racers)(()).traverse(_ => pool.take(())).use_
+
+          def burst(b: Int) = List.range(0, racers).parTraverse_ { i =>
+            pool.take(()).use_.start.flatMap { f =>
+              IO.delay(spin((b * 7 + i * 9) % 600)) *> f.cancel
+            }
+          }
+
+          for {
+            _ <- seed
+            _ <- List.range(0, bursts).traverse_(b => burst(b) *> seed)
+            st <- pool.state
+            a <- allocated.get
+            d <- destroyed.get
+          } yield (a - d - st._1, st._1, st._2.values.sum)
+        }
+        .timeoutTo(
+          2.minutes,
+          IO.raiseError(new AssertionError("timed out, a permit was probably lost"))
+        )
+    } yield {
+      val (leaked, idle, perKey) = state
+      assertEquals(idle, perKey, "pool idle count disagrees with its per-key totals")
+      assertEquals(leaked, 0, s"$leaked resources were neither destroyed nor pooled")
+    }
+  }
+}
diff --git a/core/src/main/scala/org/typelevel/keypool/KeyPool.scala b/core/src/main/scala/org/typelevel/keypool/KeyPool.scala
index 40bcd697..edc28073 100644
--- a/core/src/main/scala/org/typelevel/keypool/KeyPool.scala
+++ b/core/src/main/scala/org/typelevel/keypool/KeyPool.scala
@@ -297,20 +297,25 @@ object KeyPool {
 
     for {
       _ <- kp.kpMaxTotalSem.permit
-      optR <- Resource.eval(kp.kpVar.modify(go))
       releasedState <- Resource.eval(Ref[F].of[Reusable](kp.kpDefaultReuseState))
-      resource <- Resource.makeFull[F, (B, F[Unit])] { poll =>
-        optR.fold(poll(kp.kpRes(k).allocated))(r => Applicative[F].pure(r))
-      } { resource =>
+      taken <- Resource.makeFull[F, (Boolean, (B, F[Unit]))] { poll =>
+        kp.kpVar.modify(go).flatMap {
+          case Some(r) => Applicative[F].pure((true, r))
+          case None => poll(kp.kpRes(k).allocated).map((false, _))
+        }
+      } { case (_, (b, destroy)) =>
         for {
           reusable <- releasedState.get
           out <- reusable match {
-            case Reusable.Reuse => put(kp, k, resource._1, resource._2).attempt.void
-            case Reusable.DontReuse => resource._2.attempt.void
+            case Reusable.Reuse => put(kp, k, b, destroy).attempt.void
+            case Reusable.DontReuse => destroy.attempt.void
           }
         } yield out
       }
-    } yield new Managed(resource._1, optR.isDefined, releasedState)
+    } yield {
+      val (reused, (b, _)) = taken
+      new Managed(b, reused, releasedState)
+    }
   }
 
   final class Builder[F[_]: Temporal, A, B] private[keypool] (