Module opentelemetry::api::context

OpenTelemetry Context API

A Context is a propagation mechanism which carries execution-scoped values across API boundaries and between logically associated execution units. Cross-cutting concerns access their data in-process using the same shared context object.

Contexts are immutable, and their write operations result in the creation of a new context containing the original values and the new specified values.

Context state

Concerns can create and retrieve their local state in the current execution state represented by a context through the get and with_value methods. It is recommended to use application-specific types when storing new context values to avoid unintentionally overwriting existing state.

Managing the current context

Contexts can be associated with the caller's current execution unit on a given thread via the attach method, and previous contexts can be restored by dropping the returned ContextGuard. Context can be nested, and will restore their parent outer context when detached on drop. To access the values of the context, a snapshot can be created via the Context::current method.

Examples

use opentelemetry::api::Context;

// Application-specific `a` and `b` values
#[derive(Debug, PartialEq)]
struct ValueA(&'static str);
#[derive(Debug, PartialEq)]
struct ValueB(u64);

let _outer_guard = Context::new().with_value(ValueA("a")).attach();

// Only value a has been set
let current = Context::current();
assert_eq!(current.get::<ValueA>(), Some(&ValueA("a")));
assert_eq!(current.get::<ValueB>(), None);

{
    let _inner_guard = Context::current_with_value(ValueB(42)).attach();
    // Both values are set in inner context
    let current = Context::current();
    assert_eq!(current.get::<ValueA>(), Some(&ValueA("a")));
    assert_eq!(current.get::<ValueB>(), Some(&ValueB(42)));
}

// Resets to only the `a` value when inner guard is dropped
let current = Context::current();
assert_eq!(current.get::<ValueA>(), Some(&ValueA("a")));
assert_eq!(current.get::<ValueB>(), None);

Modules

propagation

OpenTelemetry Propagator interface

Structs

Context	An execution-scoped collection of values.
ContextGuard	A guard that resets the current context to the prior context when dropped.