With this change we change the approach to continue spans (if they already exist) instead of starting new ones. The RPC spans would still be generated but Hystrix, Async, Callables / Runnables will reuse an existing span if there is one.
the scenarios are as follows:
Assuming that we have a trace X with span Y
* if you used tracer.wrap(Callable) or trace.wrap(Runnable) then:
* previously you'd get a span Z created when the Callable / Runnable is executed
* with this change you'll continue the span Y
* if you used a HystrixCommand then
* previously you'd get a span Z together with added tags when the command got executed
* with this change you'll continue the span Y and the tags will be added to span Y
* if you used a ExecutorService then
* previously you'd get a span Z together with added tags when a method from ExecutorService got executed
* with this change you'll continue the span Y and the tags will be added to span Y
Assuming that there was no span then everything will work as previously.
In order to create a new span you just have to create it manually. Example of creating a new span for an `@Async` annotated method.
```
// obviously you should inject via constructor ;)
@Autowired Tracer tracer;
@Async
public Future<String> foo() {
Span span = tracer.createSpan("newSpan");
try {
// do your stuff
} finally {
this.tracer.close(span);
}
}
```
fixes#174
8c8c3e919b