Run JDK HTTP sender on non-daemon threads.

* Updated the default ExecutorService on JdkHttpSender to use the
  DaemonThreadFactory, instead of the JDK default.

Author: SoftlySplinter

exporters/sender/jdk/src/main/java/io/opentelemetry/exporter/sender/jdk/internal/JdkHttpSender.java

@@ -32,7 +32,6 @@
 import java.util.concurrent.CompletableFuture;
 import java.util.concurrent.ConcurrentLinkedQueue;
 import java.util.concurrent.ExecutorService;
-import java.util.concurrent.Executors;
 import java.util.concurrent.ThreadLocalRandom;
 import java.util.concurrent.TimeUnit;
 import java.util.function.Consumer;
@@ -101,7 +100,7 @@ public final class JdkHttpSender implements HttpSender {
             .map(RetryPolicy::getRetryExceptionPredicate)
             .orElse(JdkHttpSender::isRetryableException);
     if (executorService == null) {
-      this.executorService = Executors.newFixedThreadPool(5);
+      this.executorService = JdkHtttpUtil.newExecutor();
       this.managedExecutor = true;
     } else {
       this.executorService = executorService;

exporters/sender/jdk/src/main/java/io/opentelemetry/exporter/sender/jdk/internal/JdkHtttpUtil.java

@@ -0,0 +1,41 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package io.opentelemetry.exporter.sender.jdk.internal;
+
+import io.opentelemetry.sdk.internal.DaemonThreadFactory;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.SynchronousQueue;
+import java.util.concurrent.ThreadPoolExecutor;
+import java.util.concurrent.TimeUnit;
+
+/**
+ * Utilities for JDK HTTP.
+ *
+ * <p>This class is internal and is hence not for public use. Its APIs are unstable and can change
+ * at any time.
+ */
+public class JdkHtttpUtil {
+  @SuppressWarnings("NonFinalStaticField")
+  private static boolean propagateContextForTestingInDispatcher = false;
+
+  public static void setPropagateContextForTestingInDispatcher(
+      boolean propagateContextForTestingInDispatcher) {
+    JdkHtttpUtil.propagateContextForTestingInDispatcher = propagateContextForTestingInDispatcher;
+  }
+
+  /** Returns an {@link ExecutorService} using daemon threads. */
+  public static ExecutorService newExecutor() {
+    return new ThreadPoolExecutor(
+        0,
+        Integer.MAX_VALUE,
+        60,
+        TimeUnit.SECONDS,
+        new SynchronousQueue<>(),
+        new DaemonThreadFactory("jdkhttp-executor", propagateContextForTestingInDispatcher));
+  }
+
+  private JdkHtttpUtil() {}
+}