From 0caf286a1a9f1f7fe13483d7adbf3f1357b12a1c Mon Sep 17 00:00:00 2001
From: Andrew Kelley <andrew@ziglang.org>
Date: Mon, 27 Oct 2025 14:08:51 -0700
Subject: [PATCH] std.Io.Threaded: don't skip executing canceled group closures

---
 lib/std/Io/Threaded.zig | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/lib/std/Io/Threaded.zig b/lib/std/Io/Threaded.zig
index 2af24dbf17..2bb88cbb78 100644
--- a/lib/std/Io/Threaded.zig
+++ b/lib/std/Io/Threaded.zig
@@ -566,10 +566,8 @@ const GroupClosure = struct {
         const reset_event: *ResetEvent = @ptrCast(&group.context);
         if (@cmpxchgStrong(CancelId, &closure.cancel_tid, .none, tid, .acq_rel, .acquire)) |cancel_tid| {
             assert(cancel_tid == .canceling);
-            // We already know the task is canceled before running the callback. Since all closures
-            // in a Group have void return type, we can return early.
-            syncFinish(group_state, reset_event);
-            return;
+            // Even though we already know the task is canceled, we must still
+            // run the closure in case there are side effects.
         }
         current_closure = closure;
         gc.func(group, gc.contextPointer());