Warning immensely helpful when operating on finished spans

[vishramachandran]

It helps when a warning log or exception is thrown when unintentionally operating on finished spans.

In asynchronous workflows, a span that is finished may be propagated down unintentionally. In other cases, Kamon.runWithSpan(span) { ...} may be used with default finish=true param, and asynchronous flow could be started from inside. Any operations on such finished span are silently lost. Discovering that spans are missing this is hard enough, and happens at the wrong times when it is desperately needed. Debugging how the missing information in the span came about is another painful exercise.

A simple warning message that "you are trying to update a finished span" is sufficient to help debug such situations. Right now, nothing is emitted in logs.

[SimunKaracic]

A warning there would be helpful, and it shouldn't be too hard to implement!

Feel free to contribute that, if you can't we'll get to it soon