Class Context

api/src/context/java/io/grpc/Context.java:85–1124

 */
/* @DoNotMock("Use ROOT for a non-null Context") // commented out to avoid dependencies  */
@CheckReturnValue
public class Context {

  static final Logger log = Logger.getLogger(Context.class.getName());

  // Long chains of contexts are suspicious and usually indicate a misuse of Context.
  // The threshold is arbitrarily chosen.
  // VisibleForTesting
  static final int CONTEXT_DEPTH_WARN_THRESH = 1000;

  /**
   * The logical root context which is the ultimate ancestor of all contexts. This context
   * is not cancellable and so will not cascade cancellation or retain listeners.
   *
   * <p>Never assume this is the default context for new threads, because {@link Storage} may define
   * a default context that is different from ROOT.
   */
  public static final Context ROOT = new Context();

  // Visible For testing
  static Storage storage() {
    return LazyStorage.storage;
  }

  // Lazy-loaded storage. Delaying storage initialization until after class initialization makes it
  // much easier to avoid circular loading since there can still be references to Context as long as
  // they don't depend on storage, like key() and currentContextExecutor(). It also makes it easier
  // to handle exceptions.
  private static final class LazyStorage {
    static final Storage storage;

    static {
      AtomicReference<Throwable> deferredStorageFailure = new AtomicReference<>();
      storage = createStorage(deferredStorageFailure);
      Throwable failure = deferredStorageFailure.get();
      // Logging must happen after storage has been set, as loggers may use Context.
      if (failure != null) {
        log.log(Level.FINE, "Storage override doesn't exist. Using default", failure);
      }
    }

    private static Storage createStorage(
        AtomicReference<? super ClassNotFoundException> deferredStorageFailure) {
      try {
        Class<?> clazz = Class.forName("io.grpc.override.ContextStorageOverride");
        // The override's constructor is prohibited from triggering any code that can loop back to
        // Context
        return clazz.asSubclass(Storage.class).getConstructor().newInstance();
      } catch (ClassNotFoundException e) {
        deferredStorageFailure.set(e);
        return new ThreadLocalContextStorage();
      } catch (Exception e) {
        throw new RuntimeException("Storage override failed to initialize", e);
      }
    }
  }

  /**