726b3663cc8e2164d4e9452f12f5866f5e8f6f1a http: properly respond to HTTP request during shutdown (furszy)
59d24bd5dd2a4549888cf7c557461e6b4959f82f threadpool: make Submit return Expected instead of throwing (furszy)
Pull request description:
Fixes#34573.
As mentioned in https://github.com/bitcoin/bitcoin/issues/34573#issuecomment-3891596958, the ThreadPool PR (#33689) revealed an existing issue.
Before that PR, we were returning an incorrect error "Request rejected because http work queue depth exceeded" during shutdown for unhandled requests (we were not differentiating between "queue depth exceeded" and "server interrupted" errors). Now, with the ThreadPool inclusion, we return the proper error but we don't handle it properly.
This PR improves exactly that. Handling the missing error and properly returning it to the user.
The race can be reproduced as follows:
1) The server receives an http request.
2) Processing of the request is delayed, and shutdown is triggered in the meantime.
3) During shutdown, the libevent callback is unregistered and the threadpool interrupted.
4) The delayed request (step 2) resumes and tries to submit a task to the now-interrupted server.
Reproduction test can be found https://github.com/bitcoin/bitcoin/pull/34577#issuecomment-3902672521.
Also, to prevent this kind of issue from happening again, this PR changes task submission
to return the error as part of the function's return value using `util::Expected` instead of
throwing the exception. Unlike exceptions, which require extra try-catch blocks and can be
ignored, returning `Expected` forces callers to explicitly handle failures, and attributes
like `[[nodiscard]]` allow us catch unhandled ones at compile time.
ACKs for top commit:
achow101:
ACK 726b3663cc8e2164d4e9452f12f5866f5e8f6f1a
sedited:
ACK 726b3663cc8e2164d4e9452f12f5866f5e8f6f1a
pinheadmz:
re-ACK 726b3663cc8e2164d4e9452f12f5866f5e8f6f1a
andrewtoth:
ACK 726b3663cc8e2164d4e9452f12f5866f5e8f6f1a
hodlinator:
re-ACK 726b3663cc8e2164d4e9452f12f5866f5e8f6f1a
Tree-SHA512: ef026e299adde1148c9fc575e7d937e957bf0ddedfc1cf081941b568736417c2eefcd8bc8c8aea795d7347040ed05da4371bddcdbda7d385e04bf4dc8d875780
02c83fef84