MINOR: log which signals are handled on startup (#6620)

Reviewers: Gwen Shapira <cshapi@gmail.com>

clients/src/main/java/org/apache/kafka/common/utils/LoggingSignalHandler.java

@@ -23,6 +23,8 @@ import java.lang.reflect.Constructor;
 import java.lang.reflect.InvocationHandler;
 import java.lang.reflect.Method;
 import java.lang.reflect.Proxy;
+import java.util.Arrays;
+import java.util.List;
 import java.util.Map;
 import java.util.concurrent.ConcurrentHashMap;
 
@@ -30,6 +32,8 @@ public class LoggingSignalHandler {
 
     private static final Logger log = LoggerFactory.getLogger(LoggingSignalHandler.class);
 
+    private static final List<String> SIGNALS = Arrays.asList("TERM", "INT", "HUP");
+
     private final Constructor<?> signalConstructor;
     private final Class<?> signalHandlerClass;
     private final Class<?> signalClass;
@@ -61,9 +65,11 @@ public class LoggingSignalHandler {
      */
     public void register() throws ReflectiveOperationException {
         Map<String, Object> jvmSignalHandlers = new ConcurrentHashMap<>();
-        register("TERM", jvmSignalHandlers);
-        register("INT", jvmSignalHandlers);
-        register("HUP", jvmSignalHandlers);
+
+        for (String signal : SIGNALS) {
+            register(signal, jvmSignalHandlers);
+        }
+        log.info("Registered signal handlers for " + String.join(", ", SIGNALS));
     }
 
     private Object createSignalHandler(final Map<String, Object> jvmSignalHandlers) {