#vulnerable code 
                              HeaderCacheElement syncRefresh() {
    try (Closeable ss = Tracing.getTracer().spanBuilder("CredentialsRefresh").startScopedSpan()) {
      return asyncRefresh().get(TIMEOUT_SECONDS, TimeUnit.SECONDS);
    } catch (InterruptedException e) {
      LOG.warn("Interrupted while trying to refresh google credentials.", e);
      Thread.currentThread().interrupt();
      return new HeaderCacheElement(
          Status.UNAUTHENTICATED
              .withDescription("Authentication was interrupted.")
              .withCause(e)
      );
    } catch (ExecutionException e) {
      LOG.warn("ExecutionException while trying to refresh google credentials.", e);
      return new HeaderCacheElement(
          Status.UNAUTHENTICATED
              .withDescription("ExecutionException during Authentication.")
              .withCause(e)
      );
    } catch (TimeoutException e) {
      LOG.warn("TimeoutException while trying to refresh google credentials.", e);
      return new HeaderCacheElement(
          Status.UNAUTHENTICATED
              .withDescription("TimeoutException during Authentication.")
              .withCause(e)
      );
    } catch (Exception e) {
      LOG.warn("Unexpected execption while trying to refresh google credentials.", e);
      return new HeaderCacheElement(
          Status.UNAUTHENTICATED
              .withDescription("Unexpected execption during Authentication.")
              .withCause(e)
      );
    }
  } 
                            #location 3 
                            #vulnerability type INTERFACE_NOT_THREAD_SAFE
#fixed code
                              Future<HeaderCacheElement> asyncRefresh() {
    LOG.trace("asyncRefresh");

    synchronized (lock) {
      try {
        if (futureToken != null) {
          return futureToken;
        }
        if (headerCache.getCacheState() == CacheState.Good) {
          return Futures.immediateFuture(headerCache);
        }

        Future<HeaderCacheElement> future = executor.submit(new Callable<HeaderCacheElement>() {
          @Override
          public HeaderCacheElement call() throws Exception {
            return updateToken();
          }
        });

        if (!future.isDone()) {
          this.futureToken = future;
        }
        return future;
      } catch (RuntimeException e) {
        futureToken = null;
        LOG.warn("Got an unexpected exception while trying to refresh google credentials.", e);
        return Futures.immediateFuture(new HeaderCacheElement(
          Status.UNAUTHENTICATED
              .withDescription("Unexpected error trying to authenticate")
              .withCause(e)));
      }
    }
  }