langchain/client/runner_utils.py/_tracer_initializer
async def _tracer_initializer(session_name: Optional[str]) -> Optional[LangChainTracer]:
    """
    Initialize a tracer to share across tasks.

    Args:
        session_name: The session name for the tracer.

    Returns:
        A LangChainTracer instance with an active session.
    """
    if session_name:
        tracer = LangChainTracer(session_name=session_name)
        tracer.ensure_session()
        return tracer
    else:
        return None