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User span discard - #276
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Discarding user spans needs `Span::discard`, which cf-rustracing 1.4.1 adds. Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Some user spans only turn out to be uninteresting after the work they measure, e.g. a routing span when nothing matched. Creating them lazily would lose the real start time, and there was no way to drop a span once created. Add `UserSpan::discard` and the ambient `user_tracing::discard_span`. Discarding replaces the span with an inactive one under its write lock, using `Span::discard`, so every handle stops recording and nothing is reported. The sampling flag is cached per handle, so only the discarding handle's cache is reset; other handles may still report being sampled while recording nothing. A deferred root that wasn't activated yet is unaffected and can still be activated. Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
TheJokr
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`SharedSpan` cached whether a span is sampled in each handle, and cloning a handle copied the cache. Discarding a user span only reset the handle it was called on, so other handles kept reporting it as sampled through `UserSpan::is_sampled`. `discard_span` discards through a clone taken from the scope stack, which left even the caller's `UserSpan` reporting the span as sampled. Deferred roots avoided stale copies with a sentinel that made every check take the span's lock until the root was activated. Keep the flag next to the span instead, in a `UserSpanSlot` shared by every handle to a user span. Activation and discard update it under the span's write lock, and reading it never takes the lock. Internal spans never change after creation, so the handle variant implies their flag, or `Tracked` stores it for `track_all_spans`. Internal handles keep their `Arc<RwLock<Span>>`, which `rustracing_span` returns. Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
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mar-cf
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Oct 9, 2026
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| pub(crate) fn with_read<R>(&self, f: impl FnOnce(&Span) -> R) -> R { |
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Should we check sampling in with_read and with_write to avoid taking the span's lock when it isn't sampled?
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wouldn't hurt but lets do that in a separate PR
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i can do this as part of the release PR
TheJokr
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cloudflare/rustracing#13
Some user spans only turn out to be uninteresting after the work they measure, e.g. a routing
span when nothing matched. Creating them lazily would lose the real start time, and there was no
way to drop a span once created.
Add
UserSpan::discardand the ambientuser_tracing::discard_span. Discarding replaces the spanwith an inactive one under its write lock, using
Span::discard, so every handle stops recordingand nothing is reported. The sampling flag is cached per handle, so only the discarding handle's
cache is reset; other handles may still report being sampled while recording nothing. A deferred
root that wasn't activated yet is unaffected and can still be activated.