Visualize image decoding and texture upload using trace flows. (flutter#3907)

Author: chinmaygarde

lib/ui/painting/image_decoding.cc

@@ -23,7 +23,10 @@ using tonic::ToDart;
 namespace blink {
 namespace {
 
-sk_sp<SkImage> DecodeImage(sk_sp<SkData> buffer) {
+static constexpr const char* kDecodeImageTraceTag = "DecodeImage";
+
+sk_sp<SkImage> DecodeImage(sk_sp<SkData> buffer, size_t trace_id) {
+  TRACE_FLOW_STEP("flutter", kDecodeImageTraceTag, trace_id);
   TRACE_EVENT0("blink", "DecodeImage");
 
   if (buffer == nullptr || buffer->isEmpty()) {
@@ -42,10 +45,13 @@ sk_sp<SkImage> DecodeImage(sk_sp<SkData> buffer) {
 }
 
 void InvokeImageCallback(sk_sp<SkImage> image,
-                         std::unique_ptr<DartPersistentValue> callback) {
+                         std::unique_ptr<DartPersistentValue> callback,
+                         size_t trace_id) {
   tonic::DartState* dart_state = callback->dart_state().get();
-  if (!dart_state)
+  if (!dart_state) {
+    TRACE_FLOW_END("flutter", kDecodeImageTraceTag, trace_id);
     return;
+  }
   tonic::DartState::Scope scope(dart_state);
   if (!image) {
     DartInvoke(callback->value(), {Dart_Null()});
@@ -54,30 +60,37 @@ void InvokeImageCallback(sk_sp<SkImage> image,
     resultImage->set_image(std::move(image));
     DartInvoke(callback->value(), {ToDart(resultImage)});
   }
+  TRACE_FLOW_END("flutter", kDecodeImageTraceTag, trace_id);
 }
 
 void DecodeImageAndInvokeImageCallback(
     std::unique_ptr<DartPersistentValue> callback,
-    sk_sp<SkData> buffer) {
-  sk_sp<SkImage> image = DecodeImage(std::move(buffer));
-  Threads::UI()->PostTask(
-      ftl::MakeCopyable([ callback = std::move(callback), image ]() mutable {
-        InvokeImageCallback(image, std::move(callback));
-      }));
+    sk_sp<SkData> buffer,
+    size_t trace_id) {
+  sk_sp<SkImage> image = DecodeImage(std::move(buffer), trace_id);
+  Threads::UI()->PostTask(ftl::MakeCopyable([
+    callback = std::move(callback), image, trace_id
+  ]() mutable { InvokeImageCallback(image, std::move(callback), trace_id); }));
 }
 
 void DecodeImageFromList(Dart_NativeArguments args) {
+  static size_t trace_counter = 1;
+  const size_t trace_id = trace_counter++;
+  TRACE_FLOW_BEGIN("flutter", kDecodeImageTraceTag, trace_id);
+
   Dart_Handle exception = nullptr;
 
   tonic::Uint8List list =
       tonic::DartConverter<tonic::Uint8List>::FromArguments(args, 0, exception);
   if (exception) {
+    TRACE_FLOW_END("flutter", kDecodeImageTraceTag, trace_id);
     Dart_ThrowException(exception);
     return;
   }
 
   Dart_Handle callback_handle = Dart_GetNativeArgument(args, 1);
   if (!Dart_IsClosure(callback_handle)) {
+    TRACE_FLOW_END("flutter", kDecodeImageTraceTag, trace_id);
     Dart_ThrowException(ToDart("Callback must be a function"));
     return;
   }
@@ -87,9 +100,10 @@ void DecodeImageFromList(Dart_NativeArguments args) {
   Threads::IO()->PostTask(ftl::MakeCopyable([
     callback = std::make_unique<DartPersistentValue>(
         tonic::DartState::Current(), callback_handle),
-    buffer = std::move(buffer)
+    buffer = std::move(buffer), trace_id
   ]() mutable {
-    DecodeImageAndInvokeImageCallback(std::move(callback), std::move(buffer));
+    DecodeImageAndInvokeImageCallback(std::move(callback), std::move(buffer),
+                                      trace_id);
   }));
 }