[fix] ScheduledExecutors use daemon threads, to avoid blocking shutdo…

…wns (#989)

ScheduledExecutors use daemon threads, so the JVM isn't prevented from shutting down

okhttp-clients/src/main/java/com/palantir/conjure/java/okhttp/OkHttpClients.java

@@ -61,10 +61,14 @@ public final class OkHttpClients {
  + "which requires debugging.",
  uncaughtException))
  .setNameFormat("remoting-okhttp-dispatcher-%d")
+ // The Dispatcher must *not* use daemon threads otherwise it would become impossible to make
+ // outgoing network requests in a shutdown hook.
+ .setDaemon(false)
  .build();
  /**
  * The {@link ExecutorService} used for the {@link Dispatcher}s of all OkHttp clients created through this class.
- * Same as OkHttp's default, but with a logging uncaught exception handler.
+ * Same as OkHttp's default, but with a logging uncaught exception handler. In a cachedThreadPool, threads that
+ * have not been used for sixty seconds are terminated, so this won't block shutdown indefinitely.
  */
  private static final ExecutorService executionExecutor =
  Tracers.wrap(Executors.newCachedThreadPool(executionThreads));
@@ -103,18 +107,18 @@ public final class OkHttpClients {
  */
  private static final ScheduledExecutorService limitReviver = Tracers.wrap(
  Executors.newSingleThreadScheduledExecutor(
- Util.threadFactory("conjure-java-runtime/leaked limit reviver", false)));
+ Util.threadFactory("conjure-java-runtime/leaked limit reviver", true)));
 
  /**
  * The {@link ScheduledExecutorService} used for scheduling call retries. This thread pool is distinct from OkHttp's
  * internal thread pool and from the thread pool used by {@link #executionExecutor}.
  * <p>
  * Note: In contrast to the {@link java.util.concurrent.ThreadPoolExecutor} used by OkHttp's {@link
  * #executionExecutor}, {@code corePoolSize} must not be zero for a {@link ScheduledThreadPoolExecutor}, see its
- * Javadoc.
+ * Javadoc. Since this executor will never hit zero threads, it must use daemon threads.
  */
  private static final ScheduledExecutorService schedulingExecutor = Tracers.wrap(Executors.newScheduledThreadPool(
- NUM_SCHEDULING_THREADS, Util.threadFactory("conjure-java-runtime/OkHttp Scheduler", false)));
+ NUM_SCHEDULING_THREADS, Util.threadFactory("conjure-java-runtime/OkHttp Scheduler", true)));
 
  private OkHttpClients() {}