fix(client): lock async session setup against concurrent callers - #200
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@Eijebong thanks for the extensive review. I think all your points are valid. I have addressed them as best as I can. Please have a look and let me know if it's all good now |
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Looking better, thank you
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AsyncClient._get_gql_session()assigns_prev_tokenwell before it assignsthe
_gql_sessionthat token refers to, with twoawaits in between and nolock. A caller arriving in that window sees a matching token, takes the reuse
path, and asserts on a session that is still
None.This holds a lock across the whole check-and-build, so the intermediate state
is never observable.
How it showed up
In fxci-config,
ci-adminshares one
AsyncClientacross all its generators. A change there(fxci-config#1124)
started looking up the default branch of ~35 repos concurrently, and 34 of the
35 requests failed with
AssertionError: the first caller was still inside thegap when the rest arrived.
fxci-config carries a local workaround for now, building the session once at
startup while it holds its own lock. It can drop that once this is released.
See fxci-config#1134.
Test
test_async_client_get_session_concurrentgathers 25 concurrent_get_aiohttp_session()calls. It fails onmainand passes with this change.The sync client has the same ordering, but
SyncClienthas no equivalentinterleaving point, so it is left alone.