[Kotlin Coroutines] why to end span while restoring thread context?

Describe the bug Use Spring Cloud Sleuth 3.1.3

KotlinContextElement.java

The current behaviour confused me: the span is always closed while restoring thread context.

Example:

  @Autowired
  private lateinit var tracer: Tracer

  @Test
  fun spanTest() = runBlocking<Unit> {
    val root = tracer.nextSpan().name("root")
    val rootSpanInScope = tracer.withSpan(root.start())
    try {
      rootSpanInScope.use {
        delay(100)
        withContext(tracer.asContextElement()) {
          delay(100)
        }
      }
    } finally {
      root.end()
    }
  }

Zipkin’s visualization:

Expected: duration of root’s span more than 200ms

[marcingrzejszczak]

Since today I guess we’ll be doing a release I’ve fixed this

[marcingrzejszczak]

That doesn’t sound good. I mean we should propagate the context and we should only close the scope after the code was executed.