aws/csm: Fix metricChan's unsafe atomic operations (#2785)

This ensures correct atomic operations and fixes test errors on 32-bit platforms like 386 and arm.

Fixes #2784

CHANGELOG_PENDING.md

@@ -3,6 +3,7 @@
 ### SDK Enhancements
 
 ### SDK Bugs
+* `aws/csm`: Fix metricChan's unsafe atomic operations ([#2785](https://github.com/aws/aws-sdk-go/pull/2785))
+  * Fixes [#2784](https://github.com/aws/aws-sdk-go/issues/2784) test failure caused by the metricChan.paused member being a value instead of a pointer. If the metricChan value was ever copied the atomic operations performed on paused would be invalid.
 * `aws/client`: Updates logic for calculating the delay after which a request can be retried. Retry delay now includes the Retry-After duration specified in a request [#2796](https://github.com/aws/aws-sdk-go/pull/2796).
   * Fixes broken test for retry delays for throttled exceptions. Fixes [#2795](https://github.com/aws/aws-sdk-go/issues/2795)
-

aws/csm/metric_chan.go

@@ -16,25 +16,26 @@ var (
 
 type metricChan struct {
 	ch     chan metric
-	paused int64
+	paused *int64
 }
 
 func newMetricChan(size int) metricChan {
 	return metricChan{
-		ch: make(chan metric, size),
+		ch:     make(chan metric, size),
+		paused: new(int64),
 	}
 }
 
 func (ch *metricChan) Pause() {
-	atomic.StoreInt64(&ch.paused, pausedEnum)
+	atomic.StoreInt64(ch.paused, pausedEnum)
 }
 
 func (ch *metricChan) Continue() {
-	atomic.StoreInt64(&ch.paused, runningEnum)
+	atomic.StoreInt64(ch.paused, runningEnum)
 }
 
 func (ch *metricChan) IsPaused() bool {
-	v := atomic.LoadInt64(&ch.paused)
+	v := atomic.LoadInt64(ch.paused)
 	return v == pausedEnum
 }