add feature flag

Author: cijothomas

opentelemetry-sdk/Cargo.toml

@@ -53,6 +53,7 @@ rt-tokio = ["tokio", "tokio-stream"]
 rt-tokio-current-thread = ["tokio", "tokio-stream"]
 rt-async-std = ["async-std"]
 internal-logs = ["tracing"]
+experimental_metrics_periodic_reader_no_runtime = ["metrics"]
 
 [[bench]]
 name = "context"

opentelemetry-sdk/src/metrics/mod.rs

@@ -50,6 +50,7 @@ pub(crate) mod meter;
 mod meter_provider;
 pub(crate) mod noop;
 pub(crate) mod periodic_reader;
+#[cfg(feature = "experimental_metrics_periodic_reader_no_runtime")]
 pub(crate) mod periodic_reader_with_own_thread;
 pub(crate) mod pipeline;
 pub mod reader;
@@ -61,6 +62,7 @@ pub use instrument::*;
 pub use manual_reader::*;
 pub use meter_provider::*;
 pub use periodic_reader::*;
+#[cfg(feature = "experimental_metrics_periodic_reader_no_runtime")]
 pub use periodic_reader_with_own_thread::*;
 pub use pipeline::Pipeline;
 pub use view::*;

opentelemetry-sdk/src/metrics/periodic_reader_with_own_thread.rs

@@ -355,7 +355,8 @@ impl PeriodicReaderInner {
         // take arbitrary time.
         //
         // Relying on futures executor to execute async call.
-        // TODO: Add timeout and pass it to exporter.
+        // TODO: Add timeout and pass it to exporter or consider alternative
+        // design to enforce timeout here.
         let exporter_result = futures_executor::block_on(self.exporter.export(&mut rm));
         #[allow(clippy::question_mark)]
         if let Err(e) = exporter_result {
@@ -392,6 +393,7 @@ impl PeriodicReaderInner {
         }
 
         if let Ok(response) = response_rx.recv() {
+            // TODO: call exporter's force_flush method.
             if response {
                 Ok(())
             } else {
@@ -502,7 +504,7 @@ mod tests {
     };
 
     // use below command to run all tests
-    // cargo test metrics::periodic_reader_with_own_thread::tests --features=testing -- --nocapture
+    // cargo test metrics::periodic_reader_with_own_thread::tests --features=testing,experimental_metrics_periodic_reader_no_runtime -- --nocapture
 
     #[derive(Debug, Clone)]
     struct MetricExporterThatFailsOnlyOnFirst {