// The config key must be set before getting its value. Getting value of
// non-existing config keys will result in errors.
// If `timeout_in_ms=0`, this call will block until the key-value is set or the
// worker shuts down.
TF_CAPI_EXPORT extern void TFE_GetConfigKeyValue(TFE_Context* ctx,
                                                 const char* key,
                                                 int64_t timeout_in_ms,

// Checks the health of collective ops peers. Explicit health check is needed in
// multi worker collective ops to detect failures in the cluster.  If a peer is
// down, collective ops may hang.
TF_CAPI_EXPORT extern void TFE_CollectiveOpsCheckPeerHealth(
    TFE_Context* ctx, const char* task, int64_t timeout_in_ms,
    TF_Status* status);

template <typename BackwardFunction, typename TapeTensor>
struct OpTapeEntry {
  string op_type;
  std::vector<TapeTensor> output_tensor_info;
  std::vector<int64_t> input_tensor_id;

  // TODO(apassos) consider narrowing down this interface.
  BackwardFunction* backward_function;

  // Should be called before deleting the backward function. TODO(apassos) use
  // unique_ptrs to ensure this happens.