TracingEventReceiver: Explicit parent for unconnected spans#83
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TracingEventSender, being a tracing Subscriber, did not track which spans were entered per thread. When spans or events used implicit (contextual) parent lookup, the serialized events carried no parent ID, making it impossible for the receiver to reconstruct correct parent-child relationships — especially when multiple threads emit concurrently. TracingEventSender now maintains a per-thread span stack (via thread_local) and falls back to it when an event or span has no explicit parent, ensuring serialized events always carry accurate parent IDs.
BREAKING: TracingEventReceiver::new() now takes an additional `root_span: Option<Id>` parameter. Previously, spans and events arriving without a parent were replayed using contextual parent lookup (Attributes::new), non-deterministically attaching to whatever span happened to be current on the receiver thread. This made receiver output dependent on ambient subscriber state. TracingEventReceiver now accepts an explicit root_span. Parentless spans and events are attached to it via Attributes::child_of. When no root_span is provided, they are created as explicit roots (Attributes::new_root), removing the dependency on receiver-side span context entirely.
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Summary
BREAKING:
TracingEventReceiver::new()now takes an additionalroot_span: Option<Id>parameter.Previously, spans and events arriving without a parent were replayed using contextual parent lookup (
Attributes::new), non-deterministically attaching to whatever span happened to be current on the receiver thread. This made receiver output dependent on ambient subscriber state.root_spaninTracingEventReceiver::new()root_spanviaAttributes::child_ofroot_spanis provided, create explicit roots (Attributes::new_root) instead of using contextual lookupDepends on #75.