Visualize EventSource events as markers
Applies to: 
Visual Studio 
Visual Studio for Mac
Note
This article applies to Visual Studio 2017. If you're looking for the latest Visual Studio documentation, see Visual Studio documentation. We recommend upgrading to the latest version of Visual Studio. Download it here
The Concurrency Visualizer can display EventSource events as markers, and you can control how the markers are displayed. To view the EventSource markers, register the ETW provider GUID by using the Advanced Settings dialog box. The Concurrency Visualizer has default conventions to represent EventSource events as Flag Markers, Span Markers, and Message Markers. You can customize how EventSource events are displayed by adding custom fields to the events. For more information about markers, see Concurrency Visualizer Markers. For more information about EventSource events, see System.Diagnostics.Tracing.
Default visualization of EventSource events
By default, the Concurrency Visualizer uses the following conventions to represent EventSource events.
Marker type
Events that have Opcode win:Start or win:Stop are treated as the beginning or end of a span, respectively. Nested or overlapping spans cannot be displayed. Event pairs that begin on one thread and end on another cannot be displayed.
An event whose Opcode is neither win:Start nor win:Stop is treated as a marker flag unless its Level (field of EVENT_RECORD.EVENT_HEADER.EVENT_DESCRIPTOR) is win:Verbose or higher.
In all other cases, the event is treated as a message.
Importance
The following table defines how the event level maps to the marker importance.
| ETW Level | Concurrency Visualizer Importance |
|---|---|
| win:LogAlways | Normal |
| win:Critical | Critical |
| win:Error | Critical |
| win:Warning | High |
| win:Informational | Normal |
| win:Verbose | Low |
| Greater than win:verbose | Low |
Series name
The task name of the event is used for the series name. Series name is empty if no task was defined for the event.
Category
If the Level is win:Critical or win:Error, then the category is Alert (-1). Otherwise, the category is the default (0).
Text
If a printf-type formatted text message was defined for the event, it is displayed as the description of the Marker. Otherwise, the description is the name of the event and the value of each payload field.
Customize visualization of EventSource events
You can customize how EventSource events are displayed by adding the appropriate fields to the event, as described in the following sections.
Marker type
Use the cvType field, a byte, to control the kind of marker that's used to represent the event. Here are the available values for cvType:
| cvType value | Resulting Marker Type |
|---|---|
| 0 | Message |
| 1 | Span Start |
| 2 | Span End |
| 3 | Flag |
| All other values | Message |
Importance
You can use the cvImportance field, a byte, to control the importance setting for an EventSource event. However, we recommend that you control the displayed importance of an event by using its Level.
| cvImportance value | Concurrency Visualizer Importance |
|---|---|
| 0 | Normal |
| 1 | Critical |
| 2 | High |
| 3 | High |
| 4 | Normal |
| 5 | Low |
| All other values | Low |
Series name
Use the cvSeries event field, a string, to control the series name that the Concurrency Visualizer gives to an EventSource event.
Category
Use the cvCategory field, a byte, to control the category that the Concurrency Visualizer gives to an EventSource event.
Text
Use the cvTextW field, a string, to control the description that the Concurrency Visualizer gives to an EventSource event.
SpanID
Use the cvSpanId field, an int, to match pairs of events. The value for each pair of start/stop events that represent a span must be unique. Typically for concurrent code, this requires the use of synchronization primitives such as Exchange to ensure that the key (the value that's used for CvSpanID) is correct.
Note
The use of SpanID to nest spans, allow them to partially overlap on the same thread, or allow them to start on one thread and end on another is not supported.