refactor: remove multi-processor on_end optimization (superseded by #3410)

Author: bryantbiggs

opentelemetry-sdk/CHANGELOG.md

@@ -13,7 +13,7 @@
 - **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). The multi-processor span export path now builds export data once and clones for additional processors, instead of rebuilding per processor.
+- 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

@@ -229,12 +229,13 @@ impl Span {
                 ));
             }
             processors => {
-                let export_data = build_export_data(data, self.span_context.clone(), &self.tracer);
-                let (last, rest) = processors.split_last().unwrap();
-                for processor in rest {
-                    processor.on_end(export_data.clone());
+                for processor in processors {
+                    processor.on_end(build_export_data(
+                        data.clone(),
+                        self.span_context.clone(),
+                        &self.tracer,
+                    ));
                 }
-                last.on_end(export_data);
             }
         }
     }