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// Copyright The OpenTelemetry Authors
// SPDX-License-Identifier: Apache-2.0
package trace
import (
"context"
"fmt"
"go.opentelemetry.io/otel/attribute"
)
/*
Sometimes information about a runtime environment can change dynamically or be
delayed from startup. Instead of continuously recreating and distributing a
TracerProvider with an immutable Resource or delaying the startup of your
application on a slow-loading piece of information, annotate the created spans
dynamically using a SpanProcessor.
*/
var (
// owner represents the owner of the application. In this example it is
// stored as a simple string, but in real-world use this may be the
// response to an asynchronous request.
owner = "unknown"
ownerKey = attribute.Key("owner")
)
// Annotator is a SpanProcessor that adds attributes to all started spans.
type Annotator struct {
// AttrsFunc is called when a span is started. The attributes it returns
// are set on the Span being started.
AttrsFunc func() []attribute.KeyValue
}
func (a Annotator) OnStart(_ context.Context, s ReadWriteSpan) { s.SetAttributes(a.AttrsFunc()...) }
func (a Annotator) Shutdown(context.Context) error { return nil }
func (a Annotator) ForceFlush(context.Context) error { return nil }
func (a Annotator) OnEnd(s ReadOnlySpan) {
attr := s.Attributes()[0]
fmt.Printf("%s: %s\n", attr.Key, attr.Value.AsString())
}
func ExampleSpanProcessor_annotated() {
a := Annotator{
AttrsFunc: func() []attribute.KeyValue {
return []attribute.KeyValue{ownerKey.String(owner)}
},
}
tracer := NewTracerProvider(WithSpanProcessor(a)).Tracer("annotated")
// Simulate the situation where we want to annotate spans with an owner,
// but at startup we do not now this information. Instead of waiting for
// the owner to be known before starting and blocking here, start doing
// work and update when the information becomes available.
ctx := context.Background()
_, s0 := tracer.Start(ctx, "span0")
// Simulate an asynchronous call to determine the owner succeeding. We now
// know that the owner of this application has been determined to be
// Alice. Make sure all subsequent spans are annotated appropriately.
owner = "alice"
_, s1 := tracer.Start(ctx, "span1")
s0.End()
s1.End()
// Output:
// owner: unknown
// owner: alice
}
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