Provide the means to configure any service threads created as daemon …

…threads.

jetcd-core/src/main/java/io/etcd/jetcd/ClientBuilder.java

@@ -47,7 +47,7 @@
 import com.google.common.collect.Streams;
 
 /**
- * ClientBuilder knows how to create an Client instance.
+ * ClientBuilder knows how to create a Client instance.
  */
 public final class ClientBuilder implements Cloneable {
 
@@ -74,6 +74,9 @@ public final class ClientBuilder implements Cloneable {
     private Duration connectTimeout;
     private boolean waitForReady = true;
 
+    // default matches vertx default and does not change behvior compared to earlier versions of jetcd.
+    private boolean useDaemonThread = false;
+
     ClientBuilder() {
     }
 
@@ -692,6 +695,29 @@ public ClientBuilder waitForReady(boolean waitForReady) {
         return this;
     }
 
+    /**
+     * Returns if any service threads created by this client will be setup as daemon threads.
+     *
+     * @return true if this client will create any necessary service threads as daemon threads.
+     */
+    public boolean useDaemonThread() {
+        return useDaemonThread;
+    }
+
+    /**
+     * Configure whether any service threads created by this client will be setup as daemon threads.
+     * Defaults to false. Note if this is not explicitly set to true, a JVM that has created service threads
+     * through this client may not exit when/if its main thread exits.
+     *
+     * @param useDaemonThread true if any service threads created by this client should be setup as daemon threads.
+     *                        False by default to preserve backwards compatibility.
+     * @return this builder
+     */
+    public ClientBuilder useDaemonThread(boolean useDaemonThread) {
+        this.useDaemonThread = useDaemonThread;
+        return this;
+    }
+
     /**
      * build a new Client.
      *

jetcd-core/src/main/java/io/etcd/jetcd/impl/ClientConnectionManager.java

@@ -25,6 +25,7 @@
 import java.util.function.Function;
 import java.util.function.Predicate;
 
+import io.vertx.core.VertxOptions;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -174,7 +175,7 @@ ManagedChannelBuilder<?> defaultChannelBuilder(String target) {
             throw new IllegalArgumentException("At least one endpoint should be provided");
         }
         if (vertx == null) {
-            vertx = Vertx.vertx();
+            vertx = Vertx.vertx(new VertxOptions().setUseDaemonThread(builder.useDaemonThread()));
         }
         final VertxChannelBuilder channelBuilder = VertxChannelBuilder.forTarget(vertx, target);