Fix metric collections during PeriodicReader shutdown (#1375)

Author: lalitb

opentelemetry-sdk/CHANGELOG.md

@@ -22,6 +22,8 @@
   `SpanData` now stores `events` as `SpanEvents` instead of `EvictedQueue` where
   `SpanEvents` is a struct with a `Vec` of events and `dropped_count`.
 
+- [#1375](https://github.com/open-telemetry/opentelemetry-rust/pull/1375/) Fix metric collections during PeriodicReader shutdown
+
 ## v0.21.1
 
 ### Fixed

opentelemetry-sdk/src/metrics/periodic_reader.rs

@@ -374,18 +374,21 @@ impl MetricReader for PeriodicReader {
         if inner.is_shutdown {
             return Err(MetricsError::Other("reader is already shut down".into()));
         }
-        inner.is_shutdown = true;
 
         let (sender, receiver) = oneshot::channel();
         inner
             .message_sender
             .try_send(Message::Shutdown(sender))
             .map_err(|e| MetricsError::Other(e.to_string()))?;
-
         drop(inner); // don't hold lock when blocking on future
 
-        futures_executor::block_on(receiver)
-            .map_err(|err| MetricsError::Other(err.to_string()))
-            .and_then(|res| res)
+        let shutdown_result = futures_executor::block_on(receiver)
+            .map_err(|err| MetricsError::Other(err.to_string()))?;
+
+        // Acquire the lock again to set the shutdown flag
+        let mut inner = self.inner.lock()?;
+        inner.is_shutdown = true;
+
+        shutdown_result
     }
 }