fix: Use daemon threads for grpc-gcp background executors by default

grpc-gcp/src/main/java/com/google/cloud/grpc/GcpManagedChannel.java

@@ -28,7 +28,6 @@
 import com.google.cloud.grpc.proto.MethodConfig;
 import com.google.common.annotations.VisibleForTesting;
 import com.google.common.base.Joiner;
-import com.google.common.util.concurrent.ThreadFactoryBuilder;
 import com.google.errorprone.annotations.concurrent.GuardedBy;
 import com.google.protobuf.Descriptors.FieldDescriptor;
 import com.google.protobuf.MessageOrBuilder;
@@ -139,7 +138,7 @@ public class GcpManagedChannel extends ManagedChannel {
 
   private final ExecutorService stateNotificationExecutor =
       Executors.newCachedThreadPool(
-          new ThreadFactoryBuilder().setNameFormat("gcp-mc-state-notifications-%d").build());
+          GcpThreadFactory.newThreadFactory("gcp-mc-state-notifications-%d"));
 
   // Callbacks to call when state changes.
   @GuardedBy("this")
@@ -177,7 +176,7 @@ public class GcpManagedChannel extends ManagedChannel {
       String.format("pool-%d", channelPoolIndex.incrementAndGet());
   private final Map<String, Long> cumulativeMetricValues = new ConcurrentHashMap<>();
   private final ScheduledExecutorService backgroundService =
-      Executors.newSingleThreadScheduledExecutor();
+      Executors.newSingleThreadScheduledExecutor(GcpThreadFactory.newThreadFactory("gcp-mc-bg-%d"));
 
   // Metrics counters.
   private final AtomicInteger readyChannels = new AtomicInteger();

grpc-gcp/src/main/java/com/google/cloud/grpc/GcpMultiEndpointChannel.java

@@ -168,7 +168,8 @@ public class GcpMultiEndpointChannel extends ManagedChannel {
   @GuardedBy("this")
   private final Set<String> currentEndpoints = new HashSet<>();
 
-  private final ScheduledExecutorService executor = new ScheduledThreadPoolExecutor(1);
+  private final ScheduledExecutorService executor =
+      new ScheduledThreadPoolExecutor(1, GcpThreadFactory.newThreadFactory("gcp-me-%d"));
 
   /**
    * Constructor for {@link GcpMultiEndpointChannel}.

grpc-gcp/src/main/java/com/google/cloud/grpc/GcpThreadFactory.java

@@ -0,0 +1,44 @@
+/*
+ * Copyright 2026 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.google.cloud.grpc;
+
+import com.google.common.util.concurrent.ThreadFactoryBuilder;
+import java.util.concurrent.ThreadFactory;
+
+/** Thread factory helper for grpc-gcp background executors. */
+public final class GcpThreadFactory {
+  /** System property to control daemon threads for grpc-gcp background executors. */
+  public static final String USE_DAEMON_THREADS_PROPERTY =
+      "com.google.cloud.grpc.use_daemon_threads";
+
+  private GcpThreadFactory() {}
+
+  /**
+   * Creates a {@link ThreadFactory} that names threads and honors the daemon-thread setting.
+   *
+   * <p>Defaults to daemon threads to avoid keeping the JVM alive when only background work remains.
+   * Set {@code -Dcom.google.cloud.grpc.use_daemon_threads=false} to use non-daemon threads.
+   */
+  public static ThreadFactory newThreadFactory(String nameFormat) {
+    boolean useDaemon = true;
+    String prop = System.getProperty(USE_DAEMON_THREADS_PROPERTY);
+    if (prop != null) {
+      useDaemon = Boolean.parseBoolean(prop);
+    }
+    return new ThreadFactoryBuilder().setNameFormat(nameFormat).setDaemon(useDaemon).build();
+  }
+}

grpc-gcp/src/main/java/com/google/cloud/grpc/fallback/GcpFallbackChannel.java

@@ -20,6 +20,7 @@
 import static java.util.concurrent.TimeUnit.MILLISECONDS;
 import static java.util.concurrent.TimeUnit.NANOSECONDS;
 
+import com.google.cloud.grpc.GcpThreadFactory;
 import com.google.common.annotations.VisibleForTesting;
 import io.grpc.CallOptions;
 import io.grpc.Channel;
@@ -84,7 +85,8 @@ public GcpFallbackChannel(
     if (execService != null) {
       this.execService = execService;
     } else {
-      this.execService = Executors.newScheduledThreadPool(3);
+      this.execService =
+          Executors.newScheduledThreadPool(3, GcpThreadFactory.newThreadFactory("gcp-fallback-%d"));
     }
     this.options = options;
     if (options.getGcpOpenTelemetry() != null) {
@@ -150,7 +152,8 @@ public GcpFallbackChannel(
     if (execService != null) {
       this.execService = execService;
     } else {
-      this.execService = Executors.newScheduledThreadPool(3);
+      this.execService =
+          Executors.newScheduledThreadPool(3, GcpThreadFactory.newThreadFactory("gcp-fallback-%d"));
     }
     this.options = options;
     if (options.getGcpOpenTelemetry() != null) {

grpc-gcp/src/main/java/com/google/cloud/grpc/multiendpoint/MultiEndpoint.java

@@ -19,6 +19,7 @@
 import static java.util.Comparator.comparingInt;
 import static java.util.concurrent.TimeUnit.MILLISECONDS;
 
+import com.google.cloud.grpc.GcpThreadFactory;
 import com.google.cloud.grpc.multiendpoint.Endpoint.EndpointState;
 import com.google.common.base.Preconditions;
 import com.google.errorprone.annotations.CanIgnoreReturnValue;
@@ -78,7 +79,8 @@ public final class MultiEndpoint {
   private long recoverCnt = 0;
   private long replaceCnt = 0;
 
-  final ScheduledExecutorService executor = new ScheduledThreadPoolExecutor(1);
+  final ScheduledExecutorService executor =
+      new ScheduledThreadPoolExecutor(1, GcpThreadFactory.newThreadFactory("gcp-me-core-%d"));
 
   private MultiEndpoint(Builder builder) {
     this.recoveryTimeout = builder.recoveryTimeout;