From 73e69a62d3983bc273ee7bf6dd6a2139dc9b7855 Mon Sep 17 00:00:00 2001
From: Alex Mendoza <182437269+MuerteSeguraZ@users.noreply.github.com>
Date: Tue, 28 Jul 2026 12:37:25 +0200
Subject: [PATCH] [KERNEL32] Make creation of a default timer queue thread safe

---
 dll/win32/kernel32/client/timerqueue.c | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/dll/win32/kernel32/client/timerqueue.c b/dll/win32/kernel32/client/timerqueue.c
index 5a24a258b9f..83656880ba4 100644
--- a/dll/win32/kernel32/client/timerqueue.c
+++ b/dll/win32/kernel32/client/timerqueue.c
@@ -19,15 +19,19 @@ HANDLE BasepDefaultTimerQueue = NULL;
 
 /* PRIVATE FUNCTIONS **********************************************************/
 
-/* FIXME - make this thread safe */
 BOOL
 WINAPI
 BasepCreateDefaultTimerQueue(VOID)
 {
     NTSTATUS Status;
+    HANDLE TimerQueue;
+
+    /* Already initialized */
+    if (BasepDefaultTimerQueue != NULL)
+        return TRUE;
 
     /* Create the timer queue */
-    Status = RtlCreateTimerQueue(&BasepDefaultTimerQueue);
+    Status = RtlCreateTimerQueue(&TimerQueue);
     if (!NT_SUCCESS(Status))
     {
         BaseSetLastNTError(Status);
@@ -35,6 +39,14 @@ BasepCreateDefaultTimerQueue(VOID)
         return FALSE;
     }
 
+    /* Try to publish it. If another thread already did, throw ours away */
+    if (InterlockedCompareExchangePointer((PVOID *)&BasepDefaultTimerQueue,
+                                           TimerQueue,
+                                           NULL) != NULL)
+    {
+        RtlDeleteTimerQueueEx(TimerQueue, NULL);
+    }
+
     return TRUE;
 }