RHI: fix the leak of QRhiResourceUpdateBatch

There are 2 ways to dispose of a QRhiResourceUpdateBatch obtained with
QRhi::nextResourceUpdateBatch():
1) Either give it to beginPass/endPass/beginComputePass/endComputePass
so it is sent to the RHI backend and then automatically released;
2) or call QRhiResourceUpdateBatch::release() if the resource update
is not used for any pass.

The Qt3D RHI renderer was never disposing of the
QRhiResourceUpdateBatch, and could end up exhausting all the 64 batches
available in the RHI: "Resource update batch pool exhausted (max is
64)", in addition to consuming a lot of RAM if the buffers or textures
are large.

To fix this, ensure the QRhiResourceUpdateBatch'es we allocate are always
released: when requesting a new one, send the previous one to
endPass/endComputePass (1), and when destroying
the SubmissionContext, release the one we will not use (2).

Change-Id: Ic3fb145b11a8e615c83745f560f019e6c4ee37f7
Reviewed-by: Paul Lemire <paul.lemire@kdab.com>
(cherry picked from commit 6b6465032f103a084e416cbddf03f8e83191aea2)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

2 files changed, 7 insertions, 2 deletions

diff --git a/src/plugins/renderers/rhi/graphicshelpers/submissioncontext.cpp b/src/plugins/renderers/rhi/graphicshelpers/submissioncontext.cpp
index c0afedfdb..0d3ef1e1b 100644
--- a/src/plugins/renderers/rhi/graphicshelpers/submissioncontext.cpp
+++ b/src/plugins/renderers/rhi/graphicshelpers/submissioncontext.cpp
@@ -804,6 +804,11 @@ void SubmissionContext::releaseResources()
     m_renderBufferHash.clear();
     RHI_UNIMPLEMENTED;
 
+    if (m_currentUpdates) {
+        m_currentUpdates->release();
+        m_currentUpdates = nullptr;
+    }
+
     // Free RHI resources
     {
         qCDebug(Backend) << Q_FUNC_INFO;
diff --git a/src/plugins/renderers/rhi/renderer/renderer.cpp b/src/plugins/renderers/rhi/renderer/renderer.cpp
index 66b40c21c..45485a6c7 100644
--- a/src/plugins/renderers/rhi/renderer/renderer.cpp
+++ b/src/plugins/renderers/rhi/renderer/renderer.cpp
@@ -2715,7 +2715,7 @@ bool Renderer::executeCommandsSubmission(const RHIPassInfo &passInfo)
         if (rv->isCompute()) {
             // If we were running draw calls we stop the draw pass
             if (inDraw) {
-                cb->endPass();
+                cb->endPass(m_submissionContext->m_currentUpdates);
                 m_submissionContext->m_currentUpdates = m_submissionContext->rhi()->nextResourceUpdateBatch();
                 inDraw = false;
             }
@@ -2734,7 +2734,7 @@ bool Renderer::executeCommandsSubmission(const RHIPassInfo &passInfo)
         } else {
             // Same logic than above but reversed
             if (inCompute) {
-                cb->endComputePass();
+                cb->endComputePass(m_submissionContext->m_currentUpdates);
                 m_submissionContext->m_currentUpdates = m_submissionContext->rhi()->nextResourceUpdateBatch();
                 inCompute = false;
             }