AllocationSampledRepro

Minimal self-contained repro for microsoft/perfview#2385 — missing AllocationSampled (EventID 303) typed schema in Microsoft.Diagnostics.Tracing.TraceEvent 3.1.30.

Requirements

• .NET 10+ SDK and runtime — AllocationSampled is never emitted on .NET 9 or earlier, regardless of keywords. Check with dotnet --version.
• No other dependencies; NuGet packages are restored automatically on first run.

Run

cd AllocationSampledRepro
dotnet run

What it demonstrates

The program runs in three phases:

1. Capture — instruments itself via DiagnosticsClient with AllocationSamplingKeyword = 0x80000000000, allocates 200 000 strings to guarantee sampled events, and saves a temporary .nettrace file.

2. Native TraceEvent API (broken) — opens the trace with EventPipeEventSource and reads EventID 303 via source.Dynamic.All. PayloadNames is null, PayloadByName returns null, and source.Clr.All receives zero events for EventID 303 — confirming the event is not routed through ClrTraceEventParser at all.

3. Raw byte workaround (works) — re-opens the same trace and decodes each event's binary payload directly using data.EventData() + data.PointerSize, recovering TypeName and ObjectSize successfully.

Expected output

══ Native TraceEvent API (broken) ═════════════════════════════════════
  PayloadNames:                <empty array>
  PayloadByName("TypeName"):   <null>
  PayloadByName("ObjectSize"): <null>
  PayloadValue(0):             <<<EXCEPTION_DURING_VALUE_LOOKUP IndexOutOfRangeException>>>
  source.Clr.All hits for EventID 303:     0  (0 = not routed through ClrTraceEventParser)
  source.Dynamic.All hits for EventID 303: 78

══ Raw EventData() workaround (works) ══════════════════════════════════
  [1] TypeName=System.Reflection.RuntimeMethodInfo  ObjectSize=104 bytes
  ...
  Total events decoded via raw bytes: 100% (N / N)

CI: PASS
  [1] Issue confirmed   — PayloadNames empty, Clr.All: 0 hits for EventID 303
  [2] Workaround confirmed — raw bytes decoded 100% of sampled events

(Event count and types vary per run; the CI workflow verifies both assertions on every push.)

Binary payload layout

Decoded from the dotnet/runtime reference consumer (src/tests/tracing/eventpipe/randomizedallocationsampling/manual/AllocationProfiler/Program.cs):

AllocationKind    win:UInt32        4 bytes
ClrInstanceID     win:UInt16        2 bytes
TypeID            win:Pointer       4 or 8 bytes (pointer-sized)
TypeName          win:UnicodeString variable (null-terminated UTF-16LE)
Address           win:Pointer       4 or 8 bytes (pointer-sized)
ObjectSize        win:UInt64        8 bytes
SampledByteOffset win:UInt64        8 bytes

Pointer size is read from TraceEvent.PointerSize.

References

• dotnet/runtime#104955 — PR that introduced AllocationSampled in .NET 10
• ClrEtwAll.man — canonical ETW manifest defining EventID 303
• AllocationProfiler/Program.cs — dotnet/runtime reference consumer using raw byte parsing
• ClrTraceEventParser.cs.base — file requiring the new typed event definition