Address review feedback

 - use spawn_blocking() in preference to spawning a thread
 - update the comment block to refer directly to issue #331

apollo-router/src/trace.rs

@@ -65,13 +65,16 @@ pub(crate) fn try_initialize_subscriber(
 
             // The call to set_tracer_provider() manipulate a sync RwLock.
             // Even though this code is sync, it is called from within an
-            // async context. If we don't do this in a separate thread,
-            // it will cause issues with the async runtime that prevents
-            // the router from working correctly.
-            let _ = std::thread::spawn(|| {
+            // async context. If we don't call set_tracer_provider() from
+            // spawn_blocking() (or from a separate thread), it will cause
+            // issues with the async runtime which results in a router
+            // which no longer responds to input events.
+            // See https://github.com/apollographql/router/issues/331
+            // for more details and description.
+            let jh = tokio::task::spawn_blocking(|| {
                 opentelemetry::global::set_tracer_provider(provider);
-            })
-            .join();
+            });
+            futures::executor::block_on(jh)?;
 
             let telemetry = tracing_opentelemetry::layer().with_tracer(tracer);