JAVA-2932: Make DefaultDriverConfigLoader.close() resilient to terminated executors (#1557)

Author: adutra

changelog/README.md

@@ -4,6 +4,7 @@
 
 ### 4.11.2 (in progress)
 
+- [bug] JAVA-2932: Make DefaultDriverConfigLoader.close() resilient to terminated executors
 - [bug] JAVA-2945: Reinstate InternalDriverContext.getNodeFilter method
 - [bug] JAVA-2947: Release buffer after decoding multi-slice frame
 - [bug] JAVA-2946: Make MapperResultProducerService instances be located with user-provided class loader

core/src/main/java/com/datastax/oss/driver/internal/core/config/typesafe/DefaultDriverConfigLoader.java

@@ -39,6 +39,7 @@
 import java.time.Duration;
 import java.util.concurrent.CompletableFuture;
 import java.util.concurrent.CompletionStage;
+import java.util.concurrent.RejectedExecutionException;
 import java.util.concurrent.TimeUnit;
 import java.util.function.Supplier;
 import net.jcip.annotations.ThreadSafe;
@@ -235,8 +236,14 @@ public Supplier<Config> getConfigSupplier() {
   @Override
   public void close() {
     SingleThreaded singleThreaded = this.singleThreaded;
-    if (singleThreaded != null) {
-      RunOrSchedule.on(singleThreaded.adminExecutor, singleThreaded::close);
+    if (singleThreaded != null && !singleThreaded.adminExecutor.terminationFuture().isDone()) {
+      try {
+        RunOrSchedule.on(singleThreaded.adminExecutor, singleThreaded::close);
+      } catch (RejectedExecutionException e) {
+        // Checking the future is racy, there is still a tiny window that could get us here.
+        // We can safely ignore this error because, if the execution is rejected, the periodic
+        // reload task, if any, has been already cancelled.
+      }
     }
   }