Fix the example installing OpenTelemetryLayer into a global subscriber

examples/opentelemetry-otlp.rs

@@ -1,11 +1,11 @@
-use opentelemetry::{global, trace::TracerProvider, Key, KeyValue};
+use opentelemetry::{global, trace::TracerProvider as _, Key, KeyValue};
 use opentelemetry_sdk::{
     metrics::{
         reader::DefaultTemporalitySelector, Aggregation, Instrument, MeterProviderBuilder,
         PeriodicReader, SdkMeterProvider, Stream,
     },
     runtime,
-    trace::{BatchConfig, RandomIdGenerator, Sampler, Tracer},
+    trace::{BatchConfig, RandomIdGenerator, Sampler, TracerProvider},
     Resource,
 };
 use opentelemetry_semantic_conventions::{
@@ -88,9 +88,9 @@ fn init_meter_provider() -> SdkMeterProvider {
     meter_provider
 }
 
-// Construct Tracer for OpenTelemetryLayer
-fn init_tracer() -> Tracer {
-    let provider = opentelemetry_otlp::new_pipeline()
+// Construct TracerProvider for OpenTelemetryLayer
+fn init_tracer_provider() -> TracerProvider {
+    opentelemetry_otlp::new_pipeline()
         .tracing()
         .with_trace_config(
             opentelemetry_sdk::trace::Config::default()
@@ -105,18 +105,24 @@ fn init_tracer() -> Tracer {
         .with_batch_config(BatchConfig::default())
         .with_exporter(opentelemetry_otlp::new_exporter().tonic())
         .install_batch(runtime::Tokio)
-        .unwrap();
-
-    global::set_tracer_provider(provider.clone());
-    provider.tracer("tracing-otel-subscriber")
+        .unwrap()
 }
 
 // Initialize tracing-subscriber and return OtelGuard for opentelemetry-related termination processing
 fn init_tracing_subscriber() -> OtelGuard {
+    let tracer_provider = init_tracer_provider();
     let meter_provider = init_meter_provider();
-    let tracer = init_tracer();
+
+    let tracer = tracer_provider.tracer("tracing-otel-subscriber");
 
     tracing_subscriber::registry()
+        // The global level filter prevents the exporter network stack
+        // from reentering the globally installed OpenTelemetryLayer with
+        // its own spans while exporting, as the libraries should not use
+        // tracing levels below DEBUG. If the OpenTelemetry layer needs to
+        // trace spans and events with higher verbosity levels, consider using
+        // per-layer filtering to target the telemetry layer specifically,
+        // e.g. by target matching.
         .with(tracing_subscriber::filter::LevelFilter::from_level(
             Level::INFO,
         ))
@@ -125,19 +131,25 @@ fn init_tracing_subscriber() -> OtelGuard {
         .with(OpenTelemetryLayer::new(tracer))
         .init();
 
-    OtelGuard { meter_provider }
+    OtelGuard {
+        tracer_provider,
+        meter_provider,
+    }
 }
 
 struct OtelGuard {
+    tracer_provider: TracerProvider,
     meter_provider: SdkMeterProvider,
 }
 
 impl Drop for OtelGuard {
     fn drop(&mut self) {
+        if let Err(err) = self.tracer_provider.shutdown() {
+            eprintln!("{err:?}");
+        }
         if let Err(err) = self.meter_provider.shutdown() {
             eprintln!("{err:?}");
         }
-        opentelemetry::global::shutdown_tracer_provider();
     }
 }
 

tests/batch_global_subscriber.rs

@@ -0,0 +1,85 @@
+use futures_util::future::BoxFuture;
+use opentelemetry::{global as otel_global, trace::TracerProvider as _};
+use opentelemetry_sdk::{
+    export::trace::{ExportResult, SpanData, SpanExporter},
+    runtime,
+    trace::TracerProvider,
+};
+use tokio::runtime::Runtime;
+use tracing::{info_span, subscriber, Level, Subscriber};
+use tracing_opentelemetry::layer;
+use tracing_subscriber::filter;
+use tracing_subscriber::prelude::*;
+
+use std::sync::{Arc, Mutex};
+
+#[derive(Clone, Debug, Default)]
+struct TestExporter(Arc<Mutex<Vec<SpanData>>>);
+
+impl SpanExporter for TestExporter {
+    fn export(&mut self, mut batch: Vec<SpanData>) -> BoxFuture<'static, ExportResult> {
+        let spans = self.0.clone();
+        Box::pin(async move {
+            if let Ok(mut inner) = spans.lock() {
+                inner.append(&mut batch);
+            }
+            Ok(())
+        })
+    }
+}
+
+fn test_tracer(runtime: &Runtime) -> (TracerProvider, TestExporter, impl Subscriber) {
+    let _guard = runtime.enter();
+
+    let exporter = TestExporter::default();
+    let provider = TracerProvider::builder()
+        .with_batch_exporter(exporter.clone(), runtime::Tokio)
+        .build();
+    let tracer = provider.tracer("test");
+
+    let subscriber = tracing_subscriber::registry().with(
+        layer()
+            .with_tracer(tracer)
+            .with_filter(filter::Targets::new().with_target("test_telemetry", Level::INFO)),
+    );
+
+    (provider, exporter, subscriber)
+}
+
+#[test]
+fn shutdown_in_scope() {
+    let rt = Runtime::new().unwrap();
+    let (provider, exporter, subscriber) = test_tracer(&rt);
+
+    subscriber::set_global_default(subscriber).unwrap();
+
+    for _ in 0..1000 {
+        let _span = info_span!(target: "test_telemetry", "test_span").entered();
+    }
+
+    // Should flush all batched telemetry spans
+    provider.shutdown().unwrap();
+
+    let spans = exporter.0.lock().unwrap();
+    assert_eq!(spans.len(), 1000);
+}
+
+#[test]
+#[ignore] // https://github.com/open-telemetry/opentelemetry-rust/issues/1961
+fn shutdown_global() {
+    let rt = Runtime::new().unwrap();
+    let (provider, exporter, subscriber) = test_tracer(&rt);
+
+    otel_global::set_tracer_provider(provider);
+    subscriber::set_global_default(subscriber).unwrap();
+
+    for _ in 0..1000 {
+        let _span = info_span!(target: "test_telemetry", "test_span").entered();
+    }
+
+    // Should flush all batched telemetry spans
+    otel_global::shutdown_tracer_provider();
+
+    let spans = exporter.0.lock().unwrap();
+    assert_eq!(spans.len(), 1000);
+}