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Kieron Lanning edited this page May 29, 2024 · 10 revisions

Purview Telemetry Source Generator

Generates ActivitySource, High-performance logging and Metrics based on methods on an interface, this enables fast iteration cycles and substitutes for testing.

Use the latest version available on NuGet, and supports the following frameworks:

  • .NET Framework 4.7.2
  • .NET Framework 4.8
  • .NET 7
  • .NET 8
  • .NET 9

For more information see:

All marker attributes are generated as conditional, meaning they will not be present in your build. However, you can define PURVIEW_TELEMETRY_ATTRIBUTES as a build constant to retain them. They are generated as internal to avoid exposing them outside of the assembly.

Basic Examples

The following examples all contain explicit definitions, meaning each example explicitly applies the appropriate attributes. Inferring certain actions or values is also supported and will be detailed in each sub-section.

The documentation for each generation target (activity, logging and metrics) contains information on what can be inferred.

By default each interface used as a source for generation includes an extension method for registering it with an IServiceCollection. More details can be found in Generation.

You can mix-and-match generation targets within a single interface, however the ability to infer is more limited. This is called multi-targeting. In .NET, Activities, Events and Metrics refer to additional properties captured at creation, recording or observation time as tags. However, in Open Telemetry these are referred to as attributes. As this source generator makes extensive use of marker attributes to control source code generation we will use the term tags to mean these properties, and attributes as the .NET Attribute type not as the Open Telemetry definition.

An example project is available in the samples folder.

Activities

Basic example of an activity-based telemetry interface.

There is one Activity (GettingItemFromCache) and the rest are events, calling these will add an ActivityEvent to the Activity.Current activity. Alternatively, you can pass in an Activity as a parameter to the event, which will be used in it's place.

You can also return an Activity? from the GettingItemFromCache method and then pass that into the events.

The [Tag] and [Baggage] attributes on the parameters will add the values to the activity or event.

[ActivitySource("some-activity")]
interface IActivityTelemetry
{
    [Activity]
    Activity? GettingItemFromCache([Baggage]string key, [Tag]string itemType);

    [Event("cachemiss")]
    void Miss(Activity? activity);

    [Event("cachehit")]
    void Hit(Activity? activity);

    [Event]
    void Error(Activity? activity, Exception ex);

    [Event]
    void Finished(Activity? activity, [Tag]TimeSpan duration);
}

More information can be found here.

Logging

Basic example of a high-performance structured logging-based interface.

Note the ProcessingWorkItem method returns an IDisposable?, this is a scoped log entry.

All of the parameters are passed into the logger methods as properties.

[Logger]
interface ILoggingTelemetry
{
    [Log(LogLevel.Information)]
    IDisposable? ProcessingWorkItem(Guid id);

    [Log(LogLevel.Trace)]
    void ProcessingItemType(ItemTypes itemType);

    [Log(LogLevel.Error)]
    void FailedToProcessWorkItem(Exception ex);

    [Log(LogLevel.Information)]
    void ProcessingComplete(bool success, TimeSpan duration);
}

More information can be found here.

Metrics

This example shows each meter type currently supported. Note the Counter attribute is demoed twice. Once with AutoIncrement set to true, this means the measurement value is automatically set to increment by 1 each time the method is called. In the other example (where AutoIncrement is false, which is the default) the measurement value is specified explicitly as a parameter using the InstrumentMeasurementAttribute.

Non-auto increment meters must specify a measurement with one of the valid types: byte, short, int, long, float, double, and decimal.

Observable types must always have a System.Func<> with one of the following supported types:

  • Any one of the following supported measurement types: byte, short, int, long, float, double, or decimal
  • Measurement<T> where T is one of valid measurement types above.
  • IEnumerable<Measurement<T>> where T is one of valid measurement types above.

As with activities, you can add a [Tag] to the parameters and they'll be included at recording time for the instrument.

Note: tags are not supported on .NET 7 for meters and will be ignored.

[Meter]
interface IMeterTelemetry
{
    [AutoCounter]
    void AutoIncrementMeter([Tag]string someValue);

    [Counter(AutoIncrement = true)]
    void AutoIncrementCounterMeter([Tag]string someValue);

    [Counter]
    void CounterMeter([InstrumentMeasurement]int measurement, [Tag]float someValue);

    [AutoCounter]
    void AutoCounterMeter([Tag]float someValue);

    [Histogram]
    void HistogramMeter([InstrumentMeasurement]int measurement, [Tag]int someValue, [Tag]bool anotherValue);

    [ObservableCounter]
    void ObservableCounterMeter(Func<float> measurement, [Tag]double someValue);

    [ObservableGauge]
    void ObservableGaugeMeter(Func<Measurement<float>> measurement, [Tag]double someValue);

    [ObservableUpDownCounter]
    void ObservableUpDownCounter(Func<IEnumerable<Measurement<byte>>> measurement, [Tag]double someValue);

    [UpDownCounter]
    void UpDownCounterMeter([InstrumentMeasurement]decimal measurement, [Tag]byte someValue);
}

More information can be found here.

Multi-Targeting

In this example, all method-based targets are explicitly set as inferring their usage is not support when using multi-targeting.

[ActivitySource("multi-targeting")]
[Logger]
[Meter]
interface IServiceTelemetry
{
    [Activity]
    Activity? StartAnActivity(string tagStringParam, [Baggage]int entityId);

    [Event]
    void AnInterestingEvent(Activity? activity, float aTagValue);

    [Context]
    void InterestingInfo(Activity? activity, float anotherTagValue, int intTagValue);

    [Log]
    void ProcessingEntity(int entityId, string property1);

    [Counter(AutoIncrement = true)]
    void AnAutoIncrement([Tag]int value);
}

More information can be found here.

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