perf(sdk): store InstrumentationScope in Arc for cheaper tracer clones (#3378)

Author: bryantbiggs

opentelemetry-sdk/CHANGELOG.md

@@ -29,6 +29,7 @@
 - **Breaking** The SDK `testing` feature is now runtime agnostic. [#3407][3407]
   - `TokioSpanExporter` and `new_tokio_test_exporter` have been renamed to `TestSpanExporter` and `new_test_exporter`.
   - The following transitive dependencies and features have been removed: `tokio/rt`, `tokio/time`, `tokio/macros`, `tokio/rt-multi-thread`, `tokio-stream`, `experimental_async_runtime`
+- Store `InstrumentationScope` in `Arc` internally in `SdkTracer`, making tracer clones cheaper (Arc refcount increment instead of deep copy).
 - Add 32-bit platform support by using `portable-atomic` for `AtomicI64` and `AtomicU64` in the metrics module. This enables compilation on 32-bit ARM targets (e.g., `armv5te-unknown-linux-gnueabi`, `armv7-unknown-linux-gnueabihf`).
 - `Aggregation` enum and `StreamBuilder::with_aggregation()` are now stable and no longer require the `spec_unstable_metrics_views` feature flag.
 - Fix `service.name` Resource attribute fallback to follow OpenTelemetry

opentelemetry-sdk/src/trace/span.rs

@@ -709,6 +709,42 @@ mod tests {
         assert_eq!(event_vec.len(), DEFAULT_MAX_EVENT_PER_SPAN as usize);
     }
 
+    #[test]
+    fn multiple_processors_receive_span_data() {
+        use crate::trace::InMemorySpanExporterBuilder;
+
+        let exporter1 = InMemorySpanExporterBuilder::new().build();
+        let exporter2 = InMemorySpanExporterBuilder::new().build();
+
+        let provider = crate::trace::SdkTracerProvider::builder()
+            .with_simple_exporter(exporter1.clone())
+            .with_simple_exporter(exporter2.clone())
+            .build();
+
+        let tracer = provider.tracer("test");
+        let mut span = tracer.start("multi_processor_span");
+        span.set_attribute(KeyValue::new("key", "value"));
+        span.end();
+
+        let spans1 = exporter1.get_finished_spans().unwrap();
+        let spans2 = exporter2.get_finished_spans().unwrap();
+
+        assert_eq!(spans1.len(), 1);
+        assert_eq!(spans2.len(), 1);
+        assert_eq!(spans1[0].name, "multi_processor_span");
+        assert_eq!(spans2[0].name, "multi_processor_span");
+        assert_eq!(spans1[0].attributes, spans2[0].attributes);
+        // Verify instrumentation scope is correctly propagated to both processors
+        assert_eq!(spans1[0].instrumentation_scope.name(), "test");
+        assert_eq!(spans2[0].instrumentation_scope.name(), "test");
+        assert_eq!(
+            spans1[0].instrumentation_scope,
+            spans2[0].instrumentation_scope
+        );
+
+        let _ = provider.shutdown();
+    }
+
     #[test]
     fn test_span_exported_data() {
         let provider = crate::trace::SdkTracerProvider::builder()

opentelemetry-sdk/src/trace/tracer.rs

@@ -17,11 +17,12 @@ use opentelemetry::{
     Context, InstrumentationScope, KeyValue,
 };
 use std::fmt;
+use std::sync::Arc;
 
 /// `Tracer` implementation to create and manage spans
 #[derive(Clone)]
 pub struct SdkTracer {
-    scope: InstrumentationScope,
+    scope: Arc<InstrumentationScope>,
     provider: SdkTracerProvider,
 }
 
@@ -39,7 +40,10 @@ impl fmt::Debug for SdkTracer {
 impl SdkTracer {
     /// Create a new tracer (used internally by `TracerProvider`s).
     pub(crate) fn new(scope: InstrumentationScope, provider: SdkTracerProvider) -> Self {
-        SdkTracer { scope, provider }
+        SdkTracer {
+            scope: Arc::new(scope),
+            provider,
+        }
     }
 
     /// TracerProvider associated with this tracer.