Is there a way to accurately measure heap allocations in Unity for unit testing?

Question

Allocating temporary objects on the heap every frame in Unity is costly, and we all do our best to avoid this by caching heap objects and avoiding garbage generating functions. It's not always obvious when something will generate garbage though. For example:

enum MyEnum {
  Zero,
  One,
  Two
}

List<MyEnum> MyList = new List<MyEnum>();
MyList.Contains(MyEnum.Zero); // Generates garbage

MyList.Contains() generates garbage because the default equality comparer for List uses objects which causes boxing of the enum value types.

In order to prevent inadvertent heap allocations like these, I would like to be able to detect them in my unit tests.

I think there are 2 requirements for this:

1. A function to return the amount of heap allocated memory
2. A way to prevent garbage collection occurring during the test

I haven't found a clean way to ensure #2. The closest thing I've found for #1 is GC.GetTotalMemory()

        [UnityTest]
        IEnumerator MyTest()
        {
          long before = GC.GetTotalMemory(false);
          const int numObjects = 1;
          for (int i = 0 ; i < numObjects; ++i)
          {
            System.Version v = new System.Version();
          }
          long after = GC.GetTotalMemory(false);
          Assert.That(before == after); 
        }

The problem is that GC.GetTotalMemory() returns the same value before and after in this test. I suspect that Unity/Mono only allocates memory from the system heap in chunks, say 4kb, so you need to allocate <= 4kb before Unity/Mono will actually request more memory from the system heap, at which point GC.GetTotalMemory() will return a different value. I confirmed that if I change numObjects to 1000, GC.GetTotalMemory() returns different values for before and after.

So in summary, 1. how can i accurately get amount of heap allocated memory, accurate to the byte and 2. can the garbage collector run during the body of my test, and if so, is there any non-hacky way of disabling GC for the duration of my test

TL;DR Thanks for your help!

Answer 1

I posted the same question over on Unity answers and got a reply:

https://answers.unity.com/questions/1535588/is-there-a-way-to-accurately-measure-heap-allocati.html

No, basically it's not possible. You could run your unit test a bunch of times in a loop and hope that it generates enough garbage to cause a change in the value returned by GC.GetTotalMemory(), but that's about it.