perf(http/prom): avoid oneshot channel for request duration start time#4448
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perf(http/prom): avoid oneshot channel for request duration start time#4448
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RecordRequestDuration knows the start time at call() time, whereas RecordResponseDuration defers it until the request body flushes. The latter needs async delivery from the request body wrapper, but the former is known synchronously. Replace the shared oneshot::Receiver<Instant> in ResponseState with an enum supporting both immediate and deferred start times, removing one heap allocation per request. Signed-off-by: Alejandro Martinez Ruiz <amr@buoyant.io>
cratelyn
approved these changes
Mar 6, 2026
cratelyn
reviewed
Mar 6, 2026
| let state = self.labeler.mk_stream_labeler(&req).map(|labeler| { | ||
| let (tx, start) = oneshot::channel(); | ||
| tx.send(time::Instant::now()).unwrap(); | ||
| let start = super::StartTime::Known(Some(time::Instant::now())); |
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this is an astute observation. thank you for opening this, @unleashed!
cratelyn
reviewed
Mar 6, 2026
| pub(crate) enum StartTime { | ||
| /// Start time is already known. | ||
| Known(Option<time::Instant>), | ||
| /// Start time will be sent when the request body finishes streaming |
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Suggested change
| /// Start time will be sent when the request body finishes streaming | |
| /// Start time will be sent when the request body finishes streaming. |
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RecordRequestDuration knows the start time at call() time, whereas RecordResponseDuration defers it until the request body flushes. The latter needs async delivery from the request body wrapper, but the former is known synchronously.
Replace the shared oneshot::Receiver in ResponseState with an enum supporting both immediate and deferred start times, removing one heap allocation per request.