TraceLoggingOpcode macro (traceloggingprovider.h)

TraceLogging wrapper macro that sets the opcode for the event.

Syntax

void TraceLoggingOpcode(
  [in]  eventOpcode
);

Parameters

[in] eventOpcode

An 8-bit number used to mark events with special semantics. This value must be a compile-time constant in the range 0 to 255.

The opcode will be used by trace decoders to organize and correlate events. Globally-recognized opcode values are defined in winmeta.h. Most events use 0 (WINEVENT_OPCODE_INFO) to indicate that the event has no special semantics. Opcode values 10 through 239 can be given user-defined semantics.

See EVENT_DESCRIPTOR for details about the event opcode.

Return value

None

Remarks

TraceLoggingOpcode(eventOpcode) can be used as a parameter to an invocation of a TraceLoggingWrite macro to set the event's opcode.

If no TraceLoggingOpcode macros are provided to a TraceLoggingWrite call, the event's default opcode is 0 (WINEVENT_OPCODE_INFO). If multiple TraceLoggingOpcode macros are provided, the last value is used.

Opcodes WINEVENT_OPCODE_START (1) and WINEVENT_OPCODE_STOP (2) are used to indicate the beginning and end of ETW activities as follows:

1. Generate an activity ID that is unique within the trace, typically using EventActivityIdControl or UuidCreate.
2. Write a start event with opcode = START, activity ID = the generated activity ID, and related activity ID = the parent activity ID (or NULL if no parent activity ID).
3. Write any number of activity information events with opcode = INFO, activity ID = the generated activity ID.
4. Write a stop event with opcode = STOP, activity ID = the generated activity ID.

Trace decoding tools will then be able to organize these events into groups based on their activity IDs.

Requirements

See also

EVENT_DESCRIPTOR

EventActivityIdControl

TraceLoggingWrite

TraceLogging wrapper macros