并行调用 OkHttpClient 是线程安全的吗？

我有几个线程同时运行，其中一些需要从Internet请求数据。我是否需要关心他们对单例的访问的同步？OkHttpClient

例如

线程 1

...
Request request = new Request.Builder()
    .url("http://hell.com/siners.txt")
    .build();

client.newCall(request).enqueue(new Callback() {
  @Override public void onFailure(Call call, IOException e) {
    e.printStackTrace();
  }

  @Override public void onResponse(Call call, Response response) throws IOException {
    try (ResponseBody responseBody = response.body()) {
      if (!response.isSuccessful()) throw new IOException("Unexpected code " + response);
      // Some work in Thread1
    }
  }

线程 2

...
Request request = new Request.Builder()
    .url("http://hell.com/slutList.txt")
    .build();

client.newCall(request).enqueue(new Callback() {
  @Override public void onFailure(Call call, IOException e) {
    e.printStackTrace();
  }

  @Override public void onResponse(Call call, Response response) throws IOException {
    try (ResponseBody responseBody = response.body()) {
      if (!response.isSuccessful()) throw new IOException("Unexpected code " + response);
      // Some work in Thread2
    }
  }

是同时发生还是有潜在危险？newCall().enque()newCall().execute()