feat: add an example on how to config multiple span processors.

* Add an example that export spans to both Jaeger and Zipkin to show how to config multiple span processors/exporters.

* Remove the `with_batch_exporter` function in `TracerProviderBuilder` as it's the same as the `with_span_processor`.

* Rename the `with_default_batch_exporter` function in `TracerProvderBuilder` to `with_batch_exporter` to keep it consistent with the `with_simple_exporter`.

* Add `init_exporter` method in Zipkin's builder to allow user build a zipkin exporter

Cargo.toml

@@ -26,5 +26,6 @@ members = [
     "examples/http",
     "examples/tracing-grpc",
     "examples/zipkin",
+    "examples/multiple-span-processors"
 ]
 exclude = ["examples/external-otlp-grpcio-async-std"]

examples/multiple-span-processors/Cargo.toml

@@ -0,0 +1,10 @@
+[package]
+name = "multiple-span-processors"
+version = "0.1.0"
+edition = "2018"
+
+[dependencies]
+opentelemetry = { path = "../../opentelemetry", features = ["rt-tokio"] }
+opentelemetry-zipkin = { path = "../../opentelemetry-zipkin", default-features=false, features=["reqwest-client"]}
+opentelemetry-jaeger = { path = "../../opentelemetry-jaeger", features = ["tokio"] }
+tokio = { version = "1.0", features = ["full"] }

examples/multiple-span-processors/README.md

@@ -0,0 +1,17 @@
+# Work with multiple span processors
+
+Opentelemetry supports export spans into multiple different destinations. One way to do so is to use multiple span processors. 
+
+In this example, we demonstrate how to send spans to both Jaeger and Zipkin backend. 
+
+To run this example. 
+
+1. Start the Jaeger and Zipkin. Run `docker-compose up`
+
+2. Use `cargo run` to run the example.
+
+3. Check the output in Jaeger and Zipkin. The console should also output the SpanData in json format.
+
+4. Use `docker-compose down -v` to tear down the Jaeger and Zipkin backend.
+
+

examples/multiple-span-processors/docker-compose.yaml

@@ -0,0 +1,19 @@
+version: "3"
+services:
+  # Jaeger
+  jaeger-all-in-one:
+    image: jaegertracing/all-in-one:1.22
+    ports:
+      - "16686:16686"
+      - "5775:5775/udp"
+      - "5775:5775/tcp"
+      - "6831:6831/udp"
+      - "6832:6832/udp"
+      - "5778:5778"
+      - "14628:14628"
+      - "14250:14250"
+
+  zipkin:
+    image: openzipkin/zipkin
+    ports:
+      - "9411:9411"

examples/multiple-span-processors/src/main.rs

@@ -0,0 +1,64 @@
+use opentelemetry::global::{self, shutdown_tracer_provider};
+use opentelemetry::sdk::export::trace::stdout::Exporter as StdoutExporter;
+use opentelemetry::sdk::trace::{BatchSpanProcessor, TracerProvider};
+use opentelemetry::trace::{mark_span_as_active, TraceError, Tracer};
+use opentelemetry::KeyValue;
+use std::io::stdout;
+use std::time::Duration;
+
+fn init_tracer() -> Result<(), TraceError> {
+    // build a jaeger batch span processor
+    let jaeger_processor = BatchSpanProcessor::builder(
+        opentelemetry_jaeger::new_pipeline()
+            .with_service_name("trace-demo")
+            .with_tags(vec![KeyValue::new("exporter", "jaeger")])
+            .init_exporter()?,
+        opentelemetry::runtime::Tokio,
+    )
+    .build();
+
+    // build a zipkin exporter
+    let zipkin_exporter = opentelemetry_zipkin::new_pipeline()
+        .with_service_name("trace-demo")
+        .init_exporter()?;
+
+    let provider = TracerProvider::builder()
+        // We can build a span processor and pass it into provider.
+        .with_span_processor(jaeger_processor)
+        // For batch span processor, we can also provide the exporter and runtime and use this
+        // helper function to build a batch span processor
+        .with_batch_exporter(zipkin_exporter, opentelemetry::runtime::Tokio)
+        // Same helper function is also available to build a simple span processor.
+        .with_simple_exporter(StdoutExporter::new(stdout(), true))
+        .build();
+
+    let _ = global::set_tracer_provider(provider);
+
+    Ok(())
+}
+
+#[tokio::main]
+async fn main() -> Result<(), Box<dyn std::error::Error + Send + Sync + 'static>> {
+    init_tracer()?;
+
+    let tracer = global::tracer("jaeger-and-zipkin");
+
+    {
+        let span = tracer.start("first span");
+        let _guard = mark_span_as_active(span);
+        {
+            let _inner = tracer.start("first sub span");
+            tokio::time::sleep(Duration::from_millis(15)).await;
+        }
+        {
+            let _inner = tracer.start("second sub span");
+            tokio::time::sleep(Duration::from_millis(15)).await;
+        }
+    }
+
+    tokio::time::sleep(Duration::from_millis(15)).await;
+
+    shutdown_tracer_provider();
+
+    Ok(())
+}

opentelemetry-datadog/src/exporter/mod.rs

@@ -134,7 +134,7 @@ impl DatadogPipelineBuilder {
         let trace_config = self.trace_config.take();
         let exporter = self.build_exporter()?;
         let mut provider_builder =
-            sdk::trace::TracerProvider::builder().with_default_batch_exporter(exporter, runtime);
+            sdk::trace::TracerProvider::builder().with_batch_exporter(exporter, runtime);
         if let Some(config) = trace_config {
             provider_builder = provider_builder.with_config(config);
         }

opentelemetry-jaeger/src/exporter/mod.rs

@@ -297,7 +297,7 @@ impl PipelineBuilder {
         let config = self.config.take();
         let exporter = self.init_exporter()?;
         let mut builder =
-            sdk::trace::TracerProvider::builder().with_default_batch_exporter(exporter, runtime);
+            sdk::trace::TracerProvider::builder().with_batch_exporter(exporter, runtime);
         if let Some(config) = config {
             builder = builder.with_config(config)
         }

opentelemetry-otlp/src/lib.rs

@@ -581,7 +581,7 @@ fn build_batch_with_exporter<R: Runtime>(
     runtime: R,
 ) -> sdk::trace::Tracer {
     let mut provider_builder =
-        sdk::trace::TracerProvider::builder().with_default_batch_exporter(exporter, runtime);
+        sdk::trace::TracerProvider::builder().with_batch_exporter(exporter, runtime);
     if let Some(config) = trace_config {
         provider_builder = provider_builder.with_config(config);
     }

opentelemetry-zipkin/src/exporter/mod.rs

@@ -84,7 +84,10 @@ impl Default for ZipkinPipelineBuilder {
 }
 
 impl ZipkinPipelineBuilder {
-    fn build_exporter(self) -> Result<Exporter, TraceError> {
+    /// Initial a Zipkin span exporter.
+    ///
+    /// Returns error if the endpoint is not valid or if no http client is provided.
+    pub fn init_exporter(self) -> Result<Exporter, TraceError> {
         if let Some(client) = self.client {
             let endpoint = Endpoint::new(self.service_name, self.service_addr);
             let exporter = Exporter::new(
@@ -103,7 +106,7 @@ impl ZipkinPipelineBuilder {
     /// Install the Zipkin trace exporter pipeline with a simple span processor.
     pub fn install_simple(mut self) -> Result<sdk::trace::Tracer, TraceError> {
         let config = self.trace_config.take();
-        let exporter = self.build_exporter()?;
+        let exporter = self.init_exporter()?;
         let mut provider_builder =
             sdk::trace::TracerProvider::builder().with_simple_exporter(exporter);
         if let Some(config) = config {
@@ -122,9 +125,9 @@ impl ZipkinPipelineBuilder {
         runtime: R,
     ) -> Result<sdk::trace::Tracer, TraceError> {
         let config = self.trace_config.take();
-        let exporter = self.build_exporter()?;
+        let exporter = self.init_exporter()?;
         let mut provider_builder =
-            sdk::trace::TracerProvider::builder().with_default_batch_exporter(exporter, runtime);
+            sdk::trace::TracerProvider::builder().with_batch_exporter(exporter, runtime);
         if let Some(config) = config {
             provider_builder = provider_builder.with_config(config);
         }

opentelemetry/src/global/trace.rs

@@ -486,7 +486,7 @@ mod tests {
         use crate::sdk::trace::TracerProvider;
         let exporter = crate::sdk::export::trace::stdout::Exporter::new(assert_writer, true);
         TracerProvider::builder()
-            .with_default_batch_exporter(exporter, runtime)
+            .with_batch_exporter(exporter, runtime)
             .build()
     }
 

opentelemetry/src/sdk/trace/provider.rs

@@ -114,22 +114,14 @@ impl Builder {
         Builder { processors, ..self }
     }
 
-    /// The `BatchProcessor` that this provider should use.
-    pub fn with_batch_exporter(self, processor: sdk::trace::BatchSpanProcessor) -> Self {
-        let mut processors = self.processors;
-        processors.push(Box::new(processor));
-
-        Builder { processors, ..self }
-    }
-
     /// The `SpanExporter` setup using a default `BatchSpanProcessor` that this provider should use.
-    pub fn with_default_batch_exporter<T: SpanExporter + 'static, R: Runtime>(
+    pub fn with_batch_exporter<T: SpanExporter + 'static, R: Runtime>(
         self,
         exporter: T,
         runtime: R,
     ) -> Self {
         let batch = sdk::trace::BatchSpanProcessor::builder(exporter, runtime).build();
-        self.with_batch_exporter(batch)
+        self.with_span_processor(batch)
     }
 
     /// The `SpanProcessor` that this provider should use.

opentelemetry/src/sdk/trace/span_processor.rs

@@ -200,7 +200,7 @@ impl SpanProcessor for SimpleSpanProcessor {
 ///
 ///     // Then use the `with_batch_exporter` method to have the provider export spans in batches.
 ///     let provider = sdktrace::TracerProvider::builder()
-///         .with_batch_exporter(batch)
+///         .with_span_processor(batch)
 ///         .build();
 ///
 ///     let _ = global::set_tracer_provider(provider);