From b35d115f7b076c7796ff7c502c985c505a6ab7bf Mon Sep 17 00:00:00 2001
From: David <david@tecplot.com>
Date: Wed, 21 Jan 2026 10:42:08 +0100
Subject: [PATCH] =?UTF-8?q?Fix=20vkCmdCopyBuffer=20SYNC-HAZARD-WRITE-AFTER?=
 =?UTF-8?q?-WRITE=20error=20Added=20a=20per=E2=80=91TransferTask=20fence?=
 =?UTF-8?q?=20to=20serialize=20transfer=20submissions=20so=20back=E2=80=91?=
 =?UTF-8?q?to=E2=80=91back=20vkCmdCopyBuffer=20writes=20can't=20overlap=20?=
 =?UTF-8?q?on=20the=20same=20queue.?=
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---
 include/vsg/app/TransferTask.h | 3 +++
 src/vsg/app/TransferTask.cpp   | 8 ++++----
 2 files changed, 7 insertions(+), 4 deletions(-)

diff --git a/include/vsg/app/TransferTask.h b/include/vsg/app/TransferTask.h
index b098bbb0b..d783bf60f 100644
--- a/include/vsg/app/TransferTask.h
+++ b/include/vsg/app/TransferTask.h
@@ -17,6 +17,7 @@ THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLI
 #include <vsg/vk/CommandBuffer.h>
 #include <vsg/vk/ResourceRequirements.h>
 #include <vsg/vk/Semaphore.h>
+#include <vsg/vk/Fence.h>
 
 namespace vsg
 {
@@ -97,6 +98,8 @@ namespace vsg
             VkDeviceSize dataTotalSize = 0;
             VkDeviceSize imageTotalSize = 0;
 
+            ref_ptr<Fence> transferCompleteFence;
+            bool waitOnTransferFence = false;
             ref_ptr<Semaphore> transferCompleteSemaphore;
             ref_ptr<Semaphore> transferConsumerCompletedSemaphore;
 
diff --git a/src/vsg/app/TransferTask.cpp b/src/vsg/app/TransferTask.cpp
index cf320b2a5..c7b0d8e54 100644
--- a/src/vsg/app/TransferTask.cpp
+++ b/src/vsg/app/TransferTask.cpp
@@ -415,7 +415,7 @@ TransferTask::TransferResult TransferTask::_transferData(DataToCopy& dataToCopy)
     log(level, "    totalSize = ", totalSize);
 
     auto& frame = *(dataToCopy.frames[dataToCopy.frameIndex]);
-    auto& fence = frame.fence;
+    auto& fence = dataToCopy.transferCompleteFence;
     auto& staging = frame.staging;
     auto& commandBuffer = frame.transferCommandBuffer;
     auto& newSignalSemaphore = dataToCopy.transferCompleteSemaphore;
@@ -432,13 +432,13 @@ TransferTask::TransferResult TransferTask::_transferData(DataToCopy& dataToCopy)
     log(level, "    newSignalSemaphore = ", newSignalSemaphore, ", ", newSignalSemaphore ? newSignalSemaphore->vk() : VK_NULL_HANDLE);
     log(level, "    copyRegions.size() = ", copyRegions.size());
 
-    if (frame.waitOnFence && fence)
+    if (dataToCopy.waitOnTransferFence && fence)
     {
         uint64_t timeout = std::numeric_limits<uint64_t>::max();
         if (VkResult result = fence->wait(timeout); result != VK_SUCCESS) return TransferResult{result, {}};
         fence->resetFenceAndDependencies();
     }
-    frame.waitOnFence = false;
+    dataToCopy.waitOnTransferFence = false;
 
     // advance frameIndex
     dataToCopy.frameIndex = (dataToCopy.frameIndex + 1) % dataToCopy.frames.size();
@@ -545,7 +545,7 @@ TransferTask::TransferResult TransferTask::_transferData(DataToCopy& dataToCopy)
 
         result = transferQueue->submit(submitInfo, fence);
 
-        frame.waitOnFence = true;
+        dataToCopy.waitOnTransferFence = true;
 
         dataToCopy.transferConsumerCompletedSemaphore.reset();