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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)
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