Flutter C++ Memory allocation causes jank on raster thread - Android NDK Dart FFI
The actual cause, after discussions (in the comments of the question), is not because the memory allocation is too slow, but lie somewhere else - the calculations which will be heavy if the allocation is big.
For details, please refer to the comments and discussions of the question ;)
![cs guy](https://lh3.googleusercontent.com/-XdUIqdMkCWA/AAAAAAAAAAI/AAAAAAAAAAA/4252rscbv5M/photo.jpg?sz=256)
Comments
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cs guy over 1 year
I have a flutter app which uses
Dart ffi
to connect to my custom C++ audio backend. There I allocate around 10MB of total memory for my audio buffers. Each buffer has 10MB / 84 of memory. I use 84 audio players. Here is the ffi flow:C++ bridge:
extern "C" __attribute__((visibility("default"))) __attribute__((used)) void * loadMedia(char *filePath, int8_t *mediaLoadPointer, int64_t *currentPositionPtr, int8_t *mediaID) { LOGD("loadMedia %s", filePath); if (soundEngine == nullptr) { soundEngine = new SoundEngine(); } return soundEngine->loadMedia(filePath, mediaLoadPointer, currentPositionPtr, mediaID); }
In my sound engine I launch a C++ thread:
void loadMedia(){ std::thread{startDecoderWorker, buffer, }.detach(); } void startDecoderWorker(float*buffer){ buffer = new float[30000]; // 30000 might be wrong here, I entered a huge value to just showcase the problem, the calculation of 10MB / 84 code is redundant to the code }
So here is the problem, I dont know why but when I allocate memory with
new
keyword even inside a C++ thread, flutters raster thread janks and I can see that my flutter UI janks lots of frames. This is also present in performance overlay as it goes all red for 3 to 5 frames with each of it taking around 30 40ms. Tested on profile mode.Here is how I came to this conclusion: If I instantly return from my
startDecoderWorker
without runningnew
memory allocation code, when I do this there is 0 jank. Everything is smooth 60fps, performance overlay doesnt show me red bars.Here are some screenshots from Profile mode: