dotnet/runtime
Auf GitHub ansehenPerf-trap with `IBinaryInteger<T>.WriteLittleEndian`
Open
#77.969 geöffnet am 7. Nov. 2022
area-System.Numericshelp wanted
Repository-Metriken
- Stars
- (17.886 Stars)
- PR-Merge-Metriken
- (Durchschn. Merge 12T 11h) (661 gemergte PRs in 30 T)
Beschreibung
https://github.com/dotnet/runtime/pull/67939 added IBinaryInteger<T>.WriteLittleEndian as default interface method around TryWriteLittleEndian which is implemented by the numeric types.
The problem with the DIM is that value types get boxed, thus leading to unexpected allocations as encountered in https://github.com/dotnet/orleans/pull/8100#discussion_r1015299807.
Repro:
using System.Numerics;
Span<byte> span = stackalloc byte[128];
int value = 42;
for (int i = 0; i < 1_000_000; ++i)
{
WriteLittleEndian(span, value);
}
int collections = GC.CollectionCount(0);
Console.WriteLine($"Collected: {(collections == 0 ? "no" : "yes")}");
static void WriteLittleEndian<T>(Span<byte> buffer, T value) where T : struct, IBinaryInteger<T>
{
value.WriteLittleEndian(buffer);
}
Mitigation is
static void WriteLittleEndian<T>(Span<byte> buffer, T value) where T : struct, IBinaryInteger<T>
{
- value.WriteLittleEndian(buffer);
+ value.TryWriteLittleEndian(buffer, out _);
}
But that is non-intuitive.
It would be better to either remove the DIM and implement that method on the concrete types (code duplication) or to make it a static virtual interface method. The latter would be a breaking change and for .NET 7 it's too late (I fear). Or there's some compiler magic to undo the boxing.