std::unique_ptr<const TF_ReadOnlyMemoryRegionOps>
      read_only_memory_region_ops_;
  std::function<void*(size_t)> plugin_memory_allocate_;
  std::function<void(void*)> plugin_memory_free_;
  ModularFileSystem(const ModularFileSystem&) = delete;
  void operator=(const ModularFileSystem&) = delete;
};

class ModularRandomAccessFile final : public RandomAccessFile {
 public:

static inline void TF_SetStatusFromGCSStatus(
    const google::cloud::Status& gcs_status, TF_Status* status) {
  TF_SetStatus(status, static_cast<TF_Code>(gcs_status.code()),
               gcs_status.message().c_str());
}

static void* plugin_memory_allocate(size_t size) { return calloc(1, size); }
static void plugin_memory_free(void* ptr) { free(ptr); }

};

struct TFE_MonitoringBuckets {
  explicit TFE_MonitoringBuckets(
      std::function<std::unique_ptr<tensorflow::monitoring::Buckets>(void)>
          fn) {
    create_buckets = fn;
  }

  std::function<std::unique_ptr<tensorflow::monitoring::Buckets>(void)>
      create_buckets;
};

struct TFE_MonitoringSamplerCell {
  tensorflow::monitoring::SamplerCell cell;
};

template <int NumLabels>

  explicit CSession(TF_Session* session);

  ~CSession();

  void SetInputs(std::vector<std::pair<TF_Operation*, TF_Tensor*>> inputs);
  void SetOutputs(std::initializer_list<TF_Operation*> outputs);
  void SetOutputs(const std::vector<TF_Output>& outputs);
  void SetTargets(std::initializer_list<TF_Operation*> targets);

  void Run(TF_Status* s);

  void CloseAndDelete(TF_Status* s);

  /// Trim the block cache to make room for another entry.
  void Trim() ABSL_EXCLUSIVE_LOCKS_REQUIRED(mu_);

  /// Update the LRU iterator for the block at `key`.
  void UpdateLRU(const Key& key, const std::shared_ptr<Block>& block,
                 TF_Status* status) ABSL_LOCKS_EXCLUDED(mu_);

  /// Remove all blocks of a file, with mu_ already held.
  void RemoveFile_Locked(const std::string& filename)

  ASSERT_GE(TF_NowNanos(), 946684800 * 1e9);
}

namespace {

struct SomeThreadData {
  ::tensorflow::mutex mu;
  bool did_work = false;
};

void SomeThreadFunc(void* data) {
  auto* real_data = static_cast<SomeThreadData*>(data);
  ::tensorflow::mutex_lock l(real_data->mu);
  real_data->did_work = true;
}

}  // namespace

TEST(TestEnv, TestThreads) {

typedef struct TF_RandomAccessFile {
  void* plugin_file;
} TF_RandomAccessFile;

typedef struct TF_WritableFile {
  void* plugin_file;
} TF_WritableFile;

typedef struct TF_ReadOnlyMemoryRegion {
  void* plugin_memory_region;
} TF_ReadOnlyMemoryRegion;

typedef struct TF_Filesystem {
  void* plugin_filesystem;
} TF_Filesystem;

typedef struct TF_TransactionToken {
  void* token;
  TF_Filesystem* owner;

typedef struct TFE_Op TFE_Op;

namespace tensorflow {
DEFINE_CONVERSION_FUNCTIONS(tensorflow::AbstractOpAttrs, TFE_OpAttrs);

// Set an AttrValue on the op. Doesn't handle the list types.
void SetOpAttrValueScalar(TFE_Context* ctx, TFE_Op* op,
                          const tensorflow::AttrValue& default_value,
                          const char* attr_name, TF_Status* status);
}  // namespace tensorflow

  // watched inputs.
  void Watch(const AbstractTensorHandle*);
  // Records an operation with given inputs and outputs
  // on the tape and marks all its outputs as watched if at
  // least one input of the op is watched and has a trainable dtype.
  // op_name is optional and is used for debugging only.
  void RecordOperation(absl::Span<AbstractTensorHandle* const> inputs,

TF_CAPI_EXPORT extern TF_AttrBuilder* TF_NewAttrBuilder(const char* op_name);
TF_CAPI_EXPORT extern void TF_DeleteAttrBuilder(TF_AttrBuilder* builder);
TF_CAPI_EXPORT extern void TF_AttrBuilderSetType(TF_AttrBuilder* builder,
                                                 const char* attr_name,
                                                 TF_DataType value);
TF_CAPI_EXPORT extern void TF_AttrBuilderSetTypeList(TF_AttrBuilder* builder,