Signals in Modelica

Here’s the translation of the Go signals example to Modelica, formatted in Markdown suitable for Hugo:

Our example demonstrates how to handle signals in Modelica. While Modelica doesn’t have direct support for Unix signals, we can simulate a similar behavior using events and discrete-time constructs.

model SignalHandling
  Real time(start=0);
  Boolean sigInt(start=false);
  Boolean sigTerm(start=false);
  Boolean done(start=false);

  function printMessage
    input String msg;
  algorithm
    Modelica.Utilities.Streams.print(msg);
  end printMessage;

equation
  der(time) = 1;

  when time > 5 then
    sigInt = true;
  end when;

  when time > 10 then
    sigTerm = true;
  end when;

  when sigInt or sigTerm then
    printMessage("\n" + (if sigInt then "interrupt" else "terminate"));
    done = true;
  end when;

algorithm
  printMessage("awaiting signal");

  when done then
    printMessage("exiting");
    terminate("Signal received");
  end when;
end SignalHandling;

In this Modelica example, we simulate signal handling using time-based events. Here’s a breakdown of the code:

1. We define a model SignalHandling with variables to represent time, signals (SIGINT and SIGTERM), and a done flag.

2. The printMessage function is defined to output messages, simulating the fmt.Println functionality in the original example.

3. We use a continuous-time variable time to simulate the passage of time.

4. Two when equations are used to simulate receiving SIGINT (at 5 seconds) and SIGTERM (at 10 seconds).

5. Another when equation detects when either signal is received, prints the appropriate message, and sets the done flag.

6. In the algorithm section, we print the “awaiting signal” message at the start.

7. A final when statement checks for the done flag, prints the “exiting” message, and terminates the simulation.

To run this Modelica model, you would typically use a Modelica simulation environment. The simulation will run until a “signal” is received (either at 5 or 10 seconds), at which point it will print the appropriate message and terminate.

This example demonstrates how to simulate signal-like behavior in Modelica using time-based events and discrete-time constructs. While it doesn’t directly interact with operating system signals, it provides a conceptual parallel to the original example’s signal handling mechanism.