From 9ed4077d9a57e19063c1c67710fa6fb83f5a5fb7 Mon Sep 17 00:00:00 2001
From: vercingetorx <40043405+vercingetorx@users.noreply.github.com>
Date: Sun, 1 Mar 2026 13:11:18 -0800
Subject: [PATCH] Fix memory leak in asyncdispatch.withTimeout by clearing
 losing callbacks (#25567)
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withTimeout currently leaves the “losing” callback installed:

  - when fut finishes first, timeout callback remains until timer fires,
- when timeout fires first, fut callback remains on the wrapped future.

Under high-throughput use with large future payloads, this retains
closures/future references longer than needed and causes large transient
RSS growth.
This patch clears the opposite callback immediately once outcome is
decided, reducing retention without changing API behavior.
---
 lib/pure/asyncdispatch.nim | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/lib/pure/asyncdispatch.nim b/lib/pure/asyncdispatch.nim
index 004cc9bcfe..70d94b023e 100644
--- a/lib/pure/asyncdispatch.nim
+++ b/lib/pure/asyncdispatch.nim
@@ -1946,9 +1946,14 @@ proc withTimeout*[T](fut: Future[T], timeout: int): owned(Future[bool]) =
           retFuture.fail(fut.error)
         else:
           retFuture.complete(true)
+        # Timeout side lost; drop its callback to avoid retaining closures/futures.
+        timeoutFuture.clearCallbacks()
   timeoutFuture.callback =
     proc () =
-      if not retFuture.finished: retFuture.complete(false)
+      if not retFuture.finished:
+        retFuture.complete(false)
+        # Wrapped future side lost; drop its callback to avoid retaining closures/futures.
+        fut.clearCallbacks()
   return retFuture
 
 proc accept*(socket: AsyncFD,