Preallocate cause excessive GC Alloc

ALINE
#1

Hey,

It seems both the Burst example and my attempts to use CommandBuilder.Preallocate cause excessive GC alloc, per frame, on Unity 2020 LTS + macOS.

Unsure why this happens, unsure if Preallocate() is working as intended, without this line no GC alloc are observed and the scene render just fine.

Screen Shot 2021-06-05 at 23.59.52
Screen Shot 2021-06-05 at 23.59.521500Ă—648 93.5 KB

#2

Hi

This allocation is part of some error checking code. It will be removed in your final build, or if you disable burst safety checks.

#3

Thx, I will check it in build and report back if there are more GC.

1 Like
#4

Just to follow up, indeed in the build I do not see such GC alloc per frame (only a 112B GC alloc during Sorting Meshes stage)

I am curious why these 2 methods result in different GC in Editor though:

IF I call it like this:

void Update()
{
    var builder = DrawingManager.GetBuilder(true);
    builder.WireBox(postion, scale, color):
    builder.Dispose();
}

Then there is that 2.4KB GC alloc.

But IF I do it in a job:

void Update()
{
    var builder = DrawingManager.GetBuilder(true);
    var job = new DrawJob()
    {
        Builder = builder;
    }
    builder.Dispose();
}

There is no extra GC.

Was it because the job version simply doesn’t do the same error checks?

#5

Yes, the job cannot do that error check due to technical limitations, that’s why you didn’t see the alloc.