Ping Simple

Most applications will require more than one operator. In this example, we will create two operators where one operator will produce and send data while the other operator will receive and print the data. The code in this example makes use of the built-in PingTxOp and PingRxOp operators that are defined in the holoscan::ops namespace.

In this example we’ll cover:

• How to use built-in operators.
• How to use add_flow() to connect operators together.

Operators and Workflow

Here is an example workflow involving two operators that are connected linearly.

In this example, the source operator PingTxOp produces integers from 1 to 10 and passes it to the sink operator PingRxOp which prints the integers to standard output.

Connecting Operators

We can connect two operators by calling add_flow() (C++ (holoscan::Fragment::add_flow)/Python (holoscan.core.Fragment.add_flow)) in the application’s compose() method.

The add_flow() method (C++ (holoscan::Fragment::add_flow)/Python (holoscan.core.Fragment.add_flow)) takes the source operator, the destination operator, and the optional port name pairs. The port name pair is used to connect the output port of the source operator to the input port of the destination operator. The first element of the pair is the output port name of the upstream operator and the second element is the input port name of the downstream operator. An empty port name ("") can be used for specifying a port name if the operator has only one input/output port. If there is only one output port in the upstream operator and only one input port in the downstream operator, the port pairs can be omitted.

The following code shows how to define a linear workflow in the compose() method for our example. Note that when an operator appears in an add_flow() statement, it doesn’t need to be added into the workflow separately using add_operator().

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  #include <holoscan/holoscan.hpp>
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  #include <holoscan/operators/ping_tx/ping_tx.hpp>
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  #include <holoscan/operators/ping_rx/ping_rx.hpp>
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  class MyPingApp : public holoscan::Application {
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   public:
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    void compose() override {
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      using namespace holoscan;
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      // Create the tx and rx operators
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      auto tx = make_operator&lt;ops::PingTxOp&gt;("tx", make_condition<CountCondition>(10));
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      auto rx = make_operator&lt;ops::PingRxOp&gt;("rx");
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      // Connect the operators into the workflow:  tx -> rx
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      add_flow(tx, rx);
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    }
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  };
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  int main(int argc, char** argv) {
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    auto app = holoscan::make_application<MyPingApp>();
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    app->run();
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    return 0;
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  }

Running the Application

Running the application should give you the following output in your terminal:

Rx message value: 1
Rx message value: 2
Rx message value: 3
Rx message value: 4
Rx message value: 5
Rx message value: 6
Rx message value: 7
Rx message value: 8
Rx message value: 9
Rx message value: 10