attempt at saving a computebuffer with asyncgpureadback, nativearray, memory mapped file.cs

void SavePartMM(int offset = 0, int partSize = fullWidth * fullHeight * fullDepth, int chunkSizeDiv = 1024)
    {
        //crashes if empty save file for some reason, too unreliable to use
        var mmf = MemoryMappedFile.CreateFromFile(Application.platform == RuntimePlatform.OSXEditor || Application.platform == RuntimePlatform.OSXPlayer ? "/Users/user/Downloads/test.bytes" : "C:\\test.bytes", FileMode.OpenOrCreate, "apoca_save");

        int chunkSize = fullWidth * fullHeight * fullDepth / chunkSizeDiv; //2 4 8 16 32 64 128 256 512 [1024] 2048
        //const int chunkSize = /*536_752_128*//*67_094_016*//*8_323_200*//*4_193_376*//*2_096_688*/520_200/*262_086*/;

        saveLock = true;
        var stopwatch = new Stopwatch(); stopwatch.Start();
        int endPoint = offset + partSize;
        var a = new NativeArray<uint>(chunkSize, Allocator.Persistent, NativeArrayOptions.UninitializedMemory);

        AsyncGPUReadback.RequestIntoNativeArray(ref a, texture, chunkSize * 4, offset * 4, OnCompleteReadback);
        stopwatch.Stop();
        
        void OnCompleteReadback(AsyncGPUReadbackRequest request)
        {
            stopwatch.Start();
            if (request.hasError) Debug.LogError("request.hasError");
            if (!request.done) Debug.LogError("!request.done");
            //var first = a.First();
            //var last = a.Last();
            //print(new{offset, first, last});

            using (var accessor = mmf.CreateViewAccessor(offset * 4, chunkSize * 4, MemoryMappedFileAccess.Write))
            {
                unsafe
                {
                    byte* pointer = null;
                    try
                    {
                        accessor.SafeMemoryMappedViewHandle.AcquirePointer(ref pointer);
                        UnsafeUtility.MemCpy(destination: pointer, a.GetUnsafeReadOnlyPtr(), chunkSize * 4);
                    }
                    finally
                    {
                        if (pointer != null) accessor.SafeMemoryMappedViewHandle.ReleasePointer();
                    }
                }
            }

            offset += chunkSize;
            if (offset >= endPoint)
            {
                a.Dispose();
                mmf.Dispose();
                stopwatch.Stop(); print("saved " + (stopwatch.ElapsedTicks / 10000d));
                saveLock = false;
            }
            else
            {
                AsyncGPUReadback.RequestIntoNativeArray(ref a, texture, chunkSize * 4, offset * 4, OnCompleteReadback);
            }
            stopwatch.Stop();
        }
        
    }