Annotation to provide the name for the span. You should annotate all your custom Runnable or Callable classes for the instrumentation logic to pick up how to name the span. Having for example the following code

@SpanName("custom-operation")
    class CustomRunnable implements Runnable {
        @Override
        public void run() {
         // latency of this method will be recorded in a span named "custom-operation"
        }
     }

Will result in creating a span with name custom-operation. When there's no @SpanName annotation, toString is used. Here's an example of the above, but via an anonymous instance.

return new Runnable() {
         -- snip --

         @Override
         public String toString() {
             return "custom-operation";
         }
    };