Get output from a model

Use this information to get the output from a model.

Get the tensor output

To get the tensor output, you have two options:

  • Use PeekOutput to get a reference to an output tensor.
  • Use CopyOutput to copy the output into a tensor that you manage outside the scope of the worker.

The following sections provide information on the methods available to retrieve the tensor output, along with their respective strengths and weaknesses.

Use PeekOutput

Use PeekOutput to get a reference to the output of the tensor. PeekOutput returns a Tensor object, so you usually need to cast it to a Tensor<float> or a Tensor<int>.

For example:

worker.Schedule(inputTensor);
Tensor<float> outputTensor = worker.PeekOutput() as Tensor<float>;

Sentis worker memory allocator owns the reference returned by PeekOutput. It implies the following:

  • You don't need to use Dispose on the output.
  • If you change the output or you rerun the worker, both the worker output and the PeekOutput copy change.
  • Using Dispose on the worker disposes the PeekOutput copy.

If you call Schedule again, the tensor is overwritten.

Note

Be careful when you read data from an output tensor. In many instances, you might unintentionally trigger a blocking wait until the model finishes to run before it downloads the data from the graphics processing unit (GPU) or Burst to the central processing unit (CPU). To mitigate this overhead, consider reading output from a model asynchronously. Additionally, profiling a model can provide valuable insight into its performance.

Download the data of the original tensor

You can do a blocking download to a read only NativeArray or Array copy of the output tensor's data.

Wait on the data of the original tensor

To avoid blocking the model while it retrieves data, you can request an asynchronous readback of the output tensor.

Tensor<float> outputTensor = worker.PeekOutput() as Tensor<float>;
var result = await outputTensor.ReadbackAndCloneAsync();

Tensor<float> outputTensor = worker.PeekOutput() as Tensor<float>;
outputTensor.ReadbackRequest();

// when done
outputTensor.ReadbackAndClone(); // not blocking

For more information, refer to Read Outputs Asynchronously.

Use CopyOutput

Use CopyOutput to copy the output of a worker into a tensor that you manage outside the scope of the worker.

  • If you pass in null, Sentis creates and returns a new tensor that contains a copy of the worker’s output.
  • If you pass in an existing tensor, Sentis reshapes it to match the output shape and copies the output data into it.
Tensor myOutputTensor;
//...
void Update () {
   worker.Schedule(inputTensor);
   worker.CopyOutput("output", ref myOutputTensor);
}

CopyOutput reshapes the provided tensor to match calculated output shape. Ensure that the provided tensor has capacity for the output.

// The model outputs a tensor of shape (1, 10)

// CopyOutput works on empty tensors, i.e. tensors without a tensor data.
myOutputTensor = new Tensor<float>(new TensorShape(1, 10), data: null);
worker.CopyOutput("output", ref myOutputTensor);

// CopyOutputInto works on tensors of different shape as long as the dataOnBackend has large enough capacity
myOutputTensor = new Tensor<float>(new TensorShape(152));
worker.CopyOutput("output", ref myOutputTensor);
// myOutputTensor now has shape (1, 10) but still has dataOnBackend.maxCapacity == 152

When you use CopyOutput, you're responsible for managing the tensor that receives the output:

  • You must call Dispose() on the tensor when you finish using it, to free up memory.
  • The tensor isn't automatically updated if you call Worker.Schedule again. If you need fresh output, call CopyOutput again after scheduling the model.

Multiple outputs

If the model has multiple outputs, you can use each output name as a parameter in Worker.PeekOutput.

Additional resources