Allocation Measurement

When MeasureAllocations = true, each iteration records:

beforeThreadId    = CurrentManagedThreadId
beforeThreadBytes = GC.GetAllocatedBytesForCurrentThread()
beforeProcess     = GC.GetTotalAllocatedBytes()
// action runs
if CurrentManagedThreadId == beforeThreadId:
   allocations[i] = Max(0, GC.GetAllocatedBytesForCurrentThread() - beforeThreadBytes)
else:
   allocations[i] = Max(0, GC.GetTotalAllocatedBytes() - beforeProcess)

The reported MeanAllocatedBytes is the arithmetic mean across all iterations. This includes any allocations made by the benchmark framework itself that appear between the two reads - in practice, for simple benchmarks, this is usually negligible.

In synchronous benchmarks this is thread-local (GC.GetAllocatedBytesForCurrentThread) and does not include allocations from other threads. In async benchmarks, if the continuation hops threads, NBenchmark falls back to process-wide delta for that sample, which can include background allocation noise.