local tracing

There are a number of zipkin libraries supporting local tracing (operations that spawn in-process and are not RPCs).

We’ve recently had a request by @wirehead for how to do this.

// Is this how I'm supposed to instrument a long-running function?
function ExampleTraceFunction() {
  tracer.setId(tracer.createRootId());
  tracer.recordMessage('start');
  // do stuff here
  tracer.recordMessage('end');
}

workaround

I suggested a workaround, which is to use Client annotations while we figure out how we want to address this here.

function ExampleTraceFunction() {
  tracer.scoped(() => {
    tracer.setId(tracer.createRootId());
    tracer.recordAnnotation(new Annotation.ClientSend());

    // do work

    tracer.recordAnnotation(new Annotation.ClientRecv());
  });
}

There’s a background issue in finagle which might steer implementation. https://github.com/twitter/finagle/issues/541

cc @fedj

[eirslett]

We can do something like

const result = tracer.local('myoperation', () => {
  return someComputation();
});

then you’re guaranteed that start() and finish() will be called correctly.

[codefromthecrypt]

ok ready to merge #156… last warning 😃

this keeps Tracer.local as a keyword that means “trace this callable” as no-one seems bothered about it.