Initialize Jaeger Tracer based on the passed `jaeger_client.Config`.
        Save it to `opentracing.tracer` global variable.
        Only the first call to this method has any effect.

def initialize_tracer(self, io_loop=None):
        """
        Initialize Jaeger Tracer based on the passed `jaeger_client.Config`.
        Save it to `opentracing.tracer` global variable.
        Only the first call to this method has any effect.
        """

        with Config._initialized_lock:
            if Config._initialized:
                logger.warn('Jaeger tracer already initialized, skipping')
                return
            Config._initialized = True

        tracer = self.new_tracer(io_loop)

        self._initialize_global_tracer(tracer=tracer)
        return tracer