fix: correctly handle sequential calls to SingleFlightGroup

.changes/065e6349-8e2a-403b-b588-067161f260fd.json

@@ -0,0 +1,5 @@
+{
+    "id": "065e6349-8e2a-403b-b588-067161f260fd",
+    "type": "bugfix",
+    "description": "Correctly handle sequential calls to `SingleFlightGroup`"
+}

runtime/runtime-core/common/src/aws/smithy/kotlin/runtime/util/SingleFlightGroup.kt

@@ -30,7 +30,7 @@ public class SingleFlightGroup<T> {
     public suspend fun singleFlight(block: suspend () -> T): T {
         mu.lock()
         val job = inFlight
-        if (job != null) {
+        if (job?.isActive == true) {
             waitCount++
             mu.unlock()
 

runtime/runtime-core/common/test/aws/smithy/kotlin/runtime/util/SingleFlightGroupTest.kt

@@ -109,4 +109,14 @@ class SingleFlightGroupTest {
             }
         }
     }
+
+    @Test
+    fun testSequential() = runTest {
+        val group = SingleFlightGroup<String>()
+        val first = group.singleFlight { "Foo" }
+        assertEquals("Foo", first)
+
+        val second = group.singleFlight { "Bar" }
+        assertEquals("Bar", second)
+    }
 }