fix: thread pool needs to be re-created if we restart after a close call

This is done by moving the close method to static and nulling the
singleton so that it can be re-created on next Operator start if needed.
This is needed for proper testing support.

Author: metacosm

operator-framework-core/src/main/java/io/javaoperatorsdk/operator/Operator.java

@@ -94,7 +94,7 @@ public void start() {
       throw new OperatorException(error, e);
     }
 
-    ExecutorServiceManager.start(configurationService);
+    ExecutorServiceManager.init(configurationService);
     controllers.start();
   }
 
@@ -106,7 +106,7 @@ public void close() {
 
     controllers.close();
 
-    ExecutorServiceManager.instance().close();
+    ExecutorServiceManager.close();
     k8sClient.close();
   }
 

operator-framework-core/src/main/java/io/javaoperatorsdk/operator/api/config/ExecutorServiceManager.java

@@ -1,6 +1,5 @@
 package io.javaoperatorsdk.operator.api.config;
 
-import java.io.Closeable;
 import java.util.Collection;
 import java.util.List;
 import java.util.concurrent.Callable;
@@ -13,7 +12,7 @@
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
-public class ExecutorServiceManager implements Closeable {
+public class ExecutorServiceManager {
   private static final Logger log = LoggerFactory.getLogger(ExecutorServiceManager.class);
   private static ExecutorServiceManager instance;
 
@@ -25,7 +24,7 @@ private ExecutorServiceManager(ExecutorService executor, int terminationTimeoutS
     this.terminationTimeoutSeconds = terminationTimeoutSeconds;
   }
 
-  public static void start(ConfigurationService configuration) {
+  public static void init(ConfigurationService configuration) {
     if (instance == null) {
       instance = new ExecutorServiceManager(
           new InstrumentedExecutorService(configuration.getExecutorService()),
@@ -35,6 +34,15 @@ public static void start(ConfigurationService configuration) {
     }
   }
 
+  public static void close() {
+    if (instance != null) {
+      instance.stop();
+    }
+    // make sure that we remove the singleton so that the thread pool is re-created on next call to
+    // start
+    instance = null;
+  }
+
   public static ExecutorServiceManager instance() {
     if (instance == null) {
       throw new IllegalStateException(
@@ -47,8 +55,7 @@ public ExecutorService executorService() {
     return executor;
   }
 
-  @Override
-  public void close() {
+  private void stop() {
     try {
       log.debug("Closing executor");
       executor.shutdown();