Class StatefulFilter

xds/src/test/java/io/grpc/xds/StatefulFilter.java:35–176

Unlike most singleton-based filters, each StatefulFilter object has a distinct identity.

 * Unlike most singleton-based filters, each StatefulFilter object has a distinct identity.
 */
class StatefulFilter implements Filter {

  static final String DEFAULT_TYPE_URL = "type.googleapis.com/grpc.test.StatefulFilter";
  private final AtomicBoolean shutdown = new AtomicBoolean();

  final int idx;
  @Nullable volatile String lastCfg = null;

  public StatefulFilter(int idx) {
    this.idx = idx;
  }

  public boolean isShutdown() {
    return shutdown.get();
  }

  @Override
  public void close() {
    if (!shutdown.compareAndSet(false, true)) {
      throw new ConcurrentModificationException(
          "Unexpected: StatefulFilter#close called multiple times");
    }
  }

  @Nullable
  @Override
  public ServerInterceptor buildServerInterceptor(
      FilterConfig config,
      @Nullable FilterConfig overrideConfig) {
    Config cfg = (Config) config;
    // TODO(sergiitk): to be replaced when name argument passed to the constructor.
    lastCfg = cfg.getConfig();
    return null;
  }

  @Override
  public String toString() {
    StringBuilder sb = new StringBuilder().append("StatefulFilter{")
        .append("idx=").append(idx);
    if (lastCfg != null) {
      sb.append(", name=").append(lastCfg);
    }
    return sb.append("}").toString();
  }

  static final class Provider implements Filter.Provider {

    private final String typeUrl;
    private final ConcurrentMap<Integer, StatefulFilter> instances = new ConcurrentHashMap<>();

    volatile int counter;

    Provider() {
      this(DEFAULT_TYPE_URL);
    }

    Provider(String typeUrl) {
      this.typeUrl = typeUrl;