test_common_request_handler

Common Request Handler example.

This example shows a Span used with RequestHandler, which is used as a middleware (as in web frameworks) to manage a new Span per operation through its before_request()/after_response() methods.

Implementation details:

• For threading, no active Span is consumed as the tasks may be run concurrently on different threads, and an explicit SpanContext has to be saved to be used as parent.
• For gevent and asyncio, as no automatic Span propagation is done, an explicit Span has to be saved to be used as parent (observe an instrumentation library could help to do that implicitly - we stick to the simplest case, though).
• For tornado and contextvars, as parent Span propagates automatically (even if the tasks are called through different coroutines), we do leverage the active Span.

RequestHandler implementation:

    def before_request(self, request, request_context):

        # If we should ignore the active Span, use any passed SpanContext
        # as the parent. Else, use the active one.
        if self.ignore_active_span:
            # Used by threading, gevent and asyncio.
            span = self.tracer.start_span('send',
                                          child_of=self.context,
                                          ignore_active_span=True)
        else:
            # Used by tornado and contextvars.
            span = self.tracer.start_span('send')