[adapters] Panic in logging code. #5509
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A user reported a panic with the following call stack:
```
thread 'circuit-thread' (17) panicked at /home/ubuntu/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/itertools-0.14.0/src/format.rs:95:21:
Format: was already formatted once
stack backtrace:
0: std::panicking::begin_panic
1: <itertools::format::Format<I> as core::fmt::Display>::fmt
2: core::fmt::write
3: core::fmt::write
4: alloc::fmt::format::format_inner
5: <sentry_tracing::converters::FieldVisitor as tracing_core::field::Visit>::record_debug
6: tracing_core::field::ValueSet::record
7: sentry_tracing::converters::extract_event_data
8: sentry_tracing::converters::extract_event_data_with_context
9: sentry_tracing::converters::breadcrumb_from_event
10: <sentry_tracing::layer::SentryLayer<S> as tracing_subscriber::layer::Layer<S>>::on_event
11: tracing_core::event::Event::dispatch
12: dbsp_adapters::util::LongOperationWarning::check
13: dbsp_adapters::controller::CircuitThread::run
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
```
which points to this line:
```rust
self.checkpoint_delay_warning
.get_or_insert_with(|| LongOperationWarning::new(Duration::from_secs(1)))
.check(|elapsed| {
info!(
"checkpoint delayed {} seconds because of: {}",
elapsed.as_secs(),
reasons.iter().format(", ")
)
});
```
The panic can happen if the iterator returned by the `format` method is
evaluated twice. This happens inside the internals of the tracing crate. Not
sure why we haven't seen this in the past. The fix just converts the iterator
to string, so there is no way it can get evaluated twice.
Signed-off-by: Leonid Ryzhyk <[email protected]>
Contributor
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Pull request overview
This PR fixes a panic in the logging path caused by re-evaluation of an itertools::format iterator within the tracing infrastructure. The change eagerly materializes the formatted reasons into a String before passing it to the info! macro, preventing multiple evaluations.
Changes:
- Adjust
LongOperationWarning::checklogging to callto_string()onreasons.iter().format(", "), avoiding double-use of theFormatiterator. - As a result, the logged reasons are now passed as an owned
Stringinstead of a lazily formatted iterator.
blp
approved these changes
Jan 25, 2026
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blp
left a comment
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Good catch. I'll look out for that footgun now.
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A user reported a panic with the following call stack:
which points to this line:
The panic can happen if the iterator returned by the
formatmethod is evaluated twice. This happens inside the internals of the tracing crate. Not sure why we haven't seen this in the past. The fix just converts the iterator to string, so there is no way it can get evaluated twice.