Module trace 

Available on crate feature trace only.

API for tracing applications and libraries.

The trace module includes types for tracking the progression of a single request while it is handled by services that make up an application. A trace is a tree of Spans which are objects that represent the work being done by individual services or components involved in a request as it flows through a system. This module implements the OpenTelemetry trace specification.

Getting Started

In application code:

use opentelemetry::{global, sdk::export::trace::stdout, trace::Tracer};

fn main() {
    // Create a new trace pipeline that prints to stdout
    let tracer = stdout::new_pipeline().install_simple();

    tracer.in_span("doing_work", |cx| {
        // Traced app logic here...
    });

    // Shutdown trace pipeline
    global::shutdown_tracer_provider();
}

In library code:

use opentelemetry::{global, trace::{Span, Tracer, TracerProvider}};

fn my_library_function() {
    // Use the global tracer provider to get access to the user-specified
    // tracer configuration
    let tracer_provider = global::tracer_provider();

    // Get a tracer for this library
    let tracer = tracer_provider.versioned_tracer(
        "my_name",
        Some(env!("CARGO_PKG_VERSION")),
        None
    );

    // Create spans
    let mut span = tracer.start("doing_work");

    // Do work...

    // End the span
    span.end();
}

Overview

The tracing API consists of a three main traits:

• TracerProviders are the entry point of the API. They provide access to Tracers.
• Tracers are types responsible for creating Spans.
• Spans provide the API to trace an operation.

Working with Async Runtimes

Exporting spans often involves sending data over a network or performing other I/O tasks. OpenTelemetry allows you to schedule these tasks using whichever runtime you area already using such as Tokio or async-std. When using an async runtime it’s best to use the BatchSpanProcessor where the spans will be sent in batches as opposed to being sent once ended, which often ends up being more efficient.

Managing Active Spans

Spans can be marked as “active” for a given Context, and all newly created spans will automatically be children of the currently active span.

The active span for a given thread can be managed via get_active_span and mark_span_as_active.

use opentelemetry::{global, trace::{self, Span, StatusCode, Tracer, TracerProvider}};

fn may_error(rand: f32) {
    if rand < 0.5 {
        // Get the currently active span to record additional attributes,
        // status, etc.
        trace::get_active_span(|span| {
            span.set_status(StatusCode::Error, "value too small".into());
        });
    }
}

// Get a tracer
let tracer = global::tracer("my_tracer");

// Create a span
let span = tracer.start("parent_span");

// Mark the span as active
let active = trace::mark_span_as_active(span);

// Any span created here will be a child of `parent_span`...

// Drop the guard and the span will no longer be active
drop(active)

Additionally Tracer::with_span and Tracer::in_span can be used as shorthand to simplify managing the parent context.

use opentelemetry::{global, trace::Tracer};

// Get a tracer
let tracer = global::tracer("my_tracer");

// Use `in_span` to create a new span and mark it as the parent, dropping it
// at the end of the block.
tracer.in_span("parent_span", |cx| {
    // spans created here will be children of `parent_span`
});

// Use `with_span` to mark a span as active for a given period.
let span = tracer.start("parent_span");
tracer.with_span(span, |cx| {
    // spans created here will be children of `parent_span`
});

Async active spans

Async spans can be propagated with TraceContextExt and FutureExt.

use opentelemetry::{Context, global, trace::{FutureExt, TraceContextExt, Tracer}};

async fn some_work() { }

// Get a tracer
let tracer = global::tracer("my_tracer");

// Start a span
let span = tracer.start("my_span");

// Perform some async work with this span as the currently active parent.
some_work().with_context(Context::current_with_span(span));

Modules

noop

No-op trace impls

Structs

Event

A Span has the ability to add events. Events have a time associated with the moment when they are added to the Span.

Link

During the Span creation user MUST have the ability to record links to other Spans. Linked Spans can be from the same or a different trace.

SpanBuilder

SpanBuilder allows span attributes to be configured before the span has started.

SpanContext

Immutable portion of a Span which can be serialized and propagated.

SpanId

An 8-byte value which identifies a given span.

SpanRef

A reference to the currently active span in this context.

TraceFlags

Flags that can be set on a SpanContext.

TraceId

A 16-byte value which identifies a given trace.

TraceState

TraceState carries system-specific configuration data, represented as a list of key-value pairs. TraceState allows multiple tracing systems to participate in the same trace.

Enums

SpanKind

SpanKind describes the relationship between the Span, its parents, and its children in a Trace. SpanKind describes two independent properties that benefit tracing systems during analysis.

StatusCode

The StatusCode interface represents the status of a finished Span. It’s composed of a canonical code in conjunction with an optional descriptive message.

TraceError

Errors returned by the trace API.

TraceStateError

Error returned by TraceState operations.

Traits

FutureExt

Extension trait allowing futures, streams, and sinks to be traced with a span.

IdGenerator

Interface for generating IDs

Span

Interface for a single operation within a trace.

TraceContextExt

Methods for storing and retrieving trace data in a context.

Tracer

Interface for constructing Spans.

TracerProvider

Types that can create instances of Tracer.

Functions

get_active_span

Executes a closure with a reference to this thread’s current span.

mark_span_as_active

Mark a given Span as active.

Type Aliases

TraceResult

Describe the result of operations in tracing API.