text: import random
  import trio
  import contextvars
  
  request_info = contextvars.ContextVar("request_info")
  
  
  # Example logging function that tags each line with the request identifier.
  def log(msg):
      # Read from task-local storage:
      request_tag = request_info.get()
  
      print(f"request {request_tag}: {msg}")
  
  
  # An example "request handler" that does some work itself and also
  # spawns some helper tasks to do some concurrent work.
  async def handle_request(tag):
      # Write to task-local storage:
      request_info.set(tag)
  
      log("Request handler started")
      await trio.sleep(random.random())
      async with trio.open_nursery() as nursery:
          nursery.start_soon(concurrent_helper, "a")
          nursery.start_soon(concurrent_helper, "b")
      await trio.sleep(random.random())
      log("Request received finished")
  
  
  async def concurrent_helper(job):
      log(f"Helper task {job} started")
      await trio.sleep(random.random())
      log(f"Helper task {job} finished")
  
  
  # Spawn several "request handlers" simultaneously, to simulate a
  # busy server handling multiple requests at the same time.
  async def main():
      async with trio.open_nursery() as nursery:
          for i in range(3):
              nursery.start_soon(handle_request, i)
  
  
  trio.run(main)
  