From ab6041edd77750a0d162b22759a5733d1568d3d5 Mon Sep 17 00:00:00 2001
From: Mamadou Babaei <info@babaei.net>
Date: Wed, 30 Apr 2025 19:47:49 +0200
Subject: [PATCH] fix a critical deadlock issue (UE-212224) in UE 5.5/5.6
 during PipelinedFrameState acquisition

---
 Handbook/src/appendix/changelog.md            |  1 +
 .../Private/SGTracking/SGXRTracker.cpp        | 72 +++++++++++++++++++
 2 files changed, 73 insertions(+)

diff --git a/Handbook/src/appendix/changelog.md b/Handbook/src/appendix/changelog.md
index 21d1bfb8..465970f6 100644
--- a/Handbook/src/appendix/changelog.md
+++ b/Handbook/src/appendix/changelog.md
@@ -14,6 +14,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Fixed
 
 - Backend initialization error handling on Android.
+- Fix [a critical issue introduced by UE `5.5`](https://github.com/EpicGames/UnrealEngine/blob/ef1397773d160d39423feb90cb2196ddfaa1e2ae/Engine/Plugins/Runtime/OpenXR/Source/OpenXRHMD/Private/OpenXRHMD.cpp#L1740) that [also affects the upcoming UE `5.6`](https://github.com/EpicGames/UnrealEngine/blob/bedc5631b81cd39aaac8d61f303eacc86d4220f0/Engine/Plugins/Runtime/OpenXR/Source/OpenXRHMD/Private/OpenXRHMD.cpp#L1772). This is known as issue `UE-212224`, which leads to a deadlock during `PipelinedFrameState` acquisition between the game and rendering threads.
 
 ### Changed
 
diff --git a/Source/SenseGloveTracking/Private/SGTracking/SGXRTracker.cpp b/Source/SenseGloveTracking/Private/SGTracking/SGXRTracker.cpp
index ccbd07f7..65cbca24 100644
--- a/Source/SenseGloveTracking/Private/SGTracking/SGXRTracker.cpp
+++ b/Source/SenseGloveTracking/Private/SGTracking/SGXRTracker.cpp
@@ -35,6 +35,11 @@
 
 #include "SGTracking/SGXRTracker.h"
 
+#if ENGINE_MAJOR_VERSION >= 5 && ENGINE_MINOR_VERSION >= 5
+#include "Async/Async.h"
+#include "Async/Future.h"
+#include "Async/TaskGraphInterfaces.h"
+#endif  /* ENGINE_MAJOR_VERSION >= 5 && ENGINE_MINOR_VERSION >= 5 */
 #include "Containers/Array.h"
 #include "Containers/Map.h"
 #include "Engine/Engine.h"
@@ -46,6 +51,10 @@
 #endif  /* ENGINE_MAJOR_VERSION >= 5 && ENGINE_MINOR_VERSION >= 4 */
 #include "IOpenXRHMDModule.h"
 #include "IXRTrackingSystem.h"
+#if ENGINE_MAJOR_VERSION >= 5 && ENGINE_MINOR_VERSION >= 5
+#include "Misc/Optional.h"
+#include "Misc/Timespan.h"
+#endif  /* ENGINE_MAJOR_VERSION >= 5 && ENGINE_MINOR_VERSION >= 5 */
 #include "OpenXRCore.h"
 #if ENGINE_MAJOR_VERSION >= 5 && ENGINE_MINOR_VERSION <= 3
 #include "OpenXRHMD.h"
@@ -2204,6 +2213,7 @@ bool FSGXRTracker::FImpl::GetControllerTransform(
                 IMotionController::GetModularFeatureName())
         };
 
+#if ENGINE_MAJOR_VERSION >= 5 && ENGINE_MINOR_VERSION <= 4
         for (const IMotionController* MotionController: MotionControllers)
         {
             if (!MotionController)
@@ -2237,6 +2247,68 @@ bool FSGXRTracker::FImpl::GetControllerTransform(
                 break;
             }
         }
+#endif  /* ENGINE_MAJOR_VERSION >= 5 && ENGINE_MINOR_VERSION <= 4 */
+
+#if ENGINE_MAJOR_VERSION >= 5 && ENGINE_MINOR_VERSION >= 5
+        TPromise<TOptional<FTransform>> Promise;
+        const TFuture<TOptional<FTransform>> Future{Promise.GetFuture()};
+
+        AsyncTask(ENamedThreads::ActualRenderingThread,
+                  [
+                      this,
+                      WorldToMetersScale,
+                      &PositionalTrackingHardwareMotionSource,
+                      &TargetPositionalTrackingProviderName,
+                      MotionControllers,
+                      Promise = MoveTemp(Promise)]() mutable
+                  {
+                      for (const IMotionController* MotionController: MotionControllers)
+                      {
+                          if (!MotionController)
+                          {
+                              continue;
+                          }
+
+                          const ETrackingStatus TrackingStatus = MotionController->GetControllerTrackingStatus(
+                              DeviceIndex, PositionalTrackingHardwareMotionSource);
+                          if (TrackingStatus == ETrackingStatus::NotTracked)
+                          {
+                              continue;
+                          }
+
+                          const FName DeviceTypeName{MotionController->GetMotionControllerDeviceTypeName()};
+                          if (DeviceTypeName != TargetPositionalTrackingProviderName)
+                          {
+                              continue;
+                          }
+
+                          FRotator Orientation;
+                          FVector Position;
+                          const bool bGotTransform = MotionController->GetControllerOrientationAndPosition(
+                              DeviceIndex, PositionalTrackingHardwareMotionSource,
+                              Orientation, Position, WorldToMetersScale);
+                          if (bGotTransform)
+                          {
+                              FTransform Transform{Orientation, Position};
+                              Promise.SetValue(MoveTemp(Transform));
+                              return;
+                          }
+                      }
+
+                      Promise.SetValue(TOptional<FTransform>{});
+                  });
+
+        if (Future.WaitFor(FTimespan::FromMilliseconds(100)))
+        {
+            TOptional<FTransform> Result{Future.Get()};
+            if (Result.IsSet())
+            {
+                OutTransform = Result.GetValue();
+                bOutMotionSourceHandTracking = false;
+                bTracked = true;
+            }
+        }
+#endif  /* ENGINE_MAJOR_VERSION >= 5 && ENGINE_MINOR_VERSION >= 5 */
     }
 
     if (!bTracked && bFallbackToHandTrackingIfNoGloveDetected)