Address PR comment - add comment to VulkanProgram

Author: anishmgoyal

filament/backend/src/vulkan/VulkanAsyncHandles.h

@@ -63,6 +63,11 @@ struct PushConstantDescription {
     uint32_t mRangeCount;
 };
 
+// Encapsulates a VkShaderModule. Note: this is a ThreadSafeResource
+// because we may use parallel compilation, in which case ref counts may
+// be modified on multiple backend threads. This is simply to avoid
+// destroying a VkShaderModule mid-compilation of a pipeline. It is
+// still assumed that all calls will originate from the backend.
 struct VulkanProgram : public HwProgram, fvkmemory::ThreadSafeResource {
     using BindingList = fvkutils::StaticVector<uint16_t, MAX_SAMPLER_COUNT>;
 

filament/backend/src/vulkan/VulkanCommands.h

@@ -36,6 +36,7 @@
 #include <atomic>
 #include <chrono>
 #include <list>
+#include <type_traits>
 #include <utility>
 #include <variant>
 
@@ -72,11 +73,11 @@ struct VulkanCommandBuffer {
 
     ~VulkanCommandBuffer();
 
-    inline void acquire(fvkmemory::resource_ptr<fvkmemory::Resource> resource) {
-        mResources.push_back(resource);
-    }
-
-    inline void acquire(fvkmemory::resource_ptr<fvkmemory::ThreadSafeResource> resource) {
+    template <typename T,
+              typename = std::enable_if_t<
+                std::is_same_v<T, fvkmemory::Resource> ||
+                std::is_same_v<T, fvkmemory::ThreadSafeResource>>>
+    inline void acquire(fvkmemory::resource_ptr<T> resource) {
         mResources.push_back(resource);
     }