tracing: Entered guards should be !Send
#698
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crate/tracing
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This is a breaking change, and should wait until the next breaking release.
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hawkw
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hawkw
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Sep 29, 2020
The `Entered` guard returned by `Span::enter` represents entering and exiting a span _on the current thread_. Calling `Span::enter` enters the span, returning an `Entered`, and dropping the `Entered` ensures that the span is exited. This ensures that all spans, once entered, are eventually exited. However, `Entered` has an auto-impl of `Send`, because it doesn't contain any `!Send` types. This means that the `Entered` guard _could_ be sent to another thread and dropped. This would cause the original thread to never exit the span,. and the thread to which the `Entered` guard was sent would exit a span that it never observed an enter for. This is incorrect. This PR adds a `*mut ()` field to `Entered` so that it no longer implements `Send`. There's now a manual `Sync` impl so structs holding an `Entered` can still be `Sync`. Fixes #698 Signed-off-by: Eliza Weisman <eliza@buoyant.io>
hawkw
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Sep 30, 2020
## Motivation The `Entered` guard returned by `Span::enter` represents entering and exiting a span _on the current thread_. Calling `Span::enter` enters the span, returning an `Entered`, and dropping the `Entered` ensures that the span is exited. This ensures that all spans, once entered, are eventually exited. However, `Entered` has an auto-impl of `Send`, because it doesn't contain any `!Send` types. This means that the `Entered` guard _could_ be sent to another thread and dropped. This would cause the original thread to never exit the span,. and the thread to which the `Entered` guard was sent would exit a span that it never observed an enter for. This is incorrect. ## Solution This PR adds a `*mut ()` field to `Entered` so that it no longer implements `Send`. There's now a manual `Sync` impl so structs holding an `Entered` can still be `Sync`. Fixes #698 Signed-off-by: Eliza Weisman <eliza@buoyant.io>
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tracingDescription
The
Enteredguard returned bySpan::enterrepresents entering and exiting a span on the current thread. CallingSpan::enterenters the span, returning anEntered, and dropping theEnteredensures that the span is exited. This ensures that all spans, once entered, are eventually exited.However,
Enteredhas an auto-impl ofSend, because it doesn't contain any!Sendtypes. This means that theEnteredguard could be sent to another thread and dropped. This would cause the original thread to never exit the span,. and the thread to which theEnteredguard was sent would exit a span that it never observed an enter for. This is incorrect.We should consider making
Entered!Send. Technically, this is a breaking change, but the current behavior is incorrect. This would also preventEnteredguards from being held in futures that are bounded withSend, which would prevent some incorrect uses ofSpan::enterinasyncblocks...The text was updated successfully, but these errors were encountered: