54. Current Span

Brave supports a “current span” concept which represents the in-flight operation. You can use Tracer.currentSpan() to add custom tags to a span and Tracer.nextSpan() to create a child of whatever is in-flight.

In Sleuth, you can autowire the Tracer bean to retrieve the current span via tracer.currentSpan() method. To retrieve the current context just call tracer.currentSpan().context() . To get the current trace id as String you can use the traceIdString() method like this: tracer.currentSpan().context().traceIdString() .

54.1 Setting a span in scope manually

When writing new instrumentation, it is important to place a span you created in scope as the current span. Not only does doing so let users access it with Tracer.currentSpan() , but it also allows customizations such as SLF4J MDC to see the current trace IDs.

Tracer.withSpanInScope(Span) facilitates this and is most conveniently employed by using the try-with-resources idiom. Whenever external code might be invoked (such as proceeding an interceptor or otherwise), place the span in scope, as shown in the following example:

@Autowired Tracer tracer;

try (SpanInScope ws = tracer.withSpanInScope(span)) {
  return inboundRequest.invoke();
} finally { // note the scope is independent of the span

In edge cases, you may need to clear the current span temporarily (for example, launching a task that should not be associated with the current request). To do tso, pass null to withSpanInScope , as shown in the following example:

@Autowired Tracer tracer;

try (SpanInScope cleared = tracer.withSpanInScope(null)) {