Using Holoscan Operators in GXF Applications

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For users who are familiar with the GXF development ecosystem (used in Holoscan SDK 0.2), we provide an export feature to leverage native Holoscan operators as GXF codelets to execute in GXF applications and GraphComposer.

We demonstrate how to wrap a native C++ holoscan operator as a GXF codelet in the wrap_operator_as_gxf_extension, as described below.

1. Creating compatible Holoscan Operators

Note

This section assumes you are already familiar with how to create a native C++ operator.

To be compatible with GXF codelets, inputs and outputs specified in Operator::setup(OperatorSpec& spec) must be of type holoscan::gxf::Entity, as shown in the PingTxNativeOp and the PingRxNativeOp implementations of this example, in contrast to the PingTxOp and PingRxOp built-in operators of the SDK.

For more details regarding the use of holoscan::gxf::Entity, follow the documentation on Interoperability between GXF and native C++ operators.

2. Creating the GXF extension that wraps the operator

To wrap the native operator as a GXF codelet in a GXF extension, we provide the CMake wrap_operator_as_gxf_extension function in the SDK. An example of how it wraps PingTxNativeOp and PingRxNativeOp can be found here.

It leverages the CMake target names of the operators defined in their respective CMakeLists.txt (ping_tx_native_op, ping_rx_native_op)
The function parameters are documented at the top of the WrapOperatorAsGXFExtension.cmake file (ignore implementation below).

Warning

A unique GXF extension is currently needed for each native operator to export (operators cannot be bundled in a single extension at this time).
Wrapping other GXF entities than operators (as codelets) is not currently supported.

3. Using your wrapped operator in a GXF application

Note

This section assumes you are familiar with how to create a GXF application.

As shown in the gxf_app/CMakeLists.txt here, you need to list the following extensions in create_gxe_application() to use your wrapped codelets:

GXF::std
gxf_holoscan_wrapper
the name of the CMake target for the created extension, defined by the EXTENSION_TARGET_NAME argument passed to wrap_operator_as_gxf_extension in the previous section

The codelet class name (defined by the CODELET_NAMESPACE::CODELET_NAME arguments passed to wrap_operator_as_gxf_extension in the previous section) can then be used as a component type in a GXF app node, as shown in the YAML app definition of the example, connecting the two ping operators.