The Funnel Process

Funnel  merges its left and right inputs on its output.

public class Funnel extends ReactiveProcess
{
  private Channel in, left, right, out;
  private boolean fromLeft = true;

  public Funnel(Channel left,Channel right,Channel out)
  { 
    this.left = left; 
    this.right = right; 
    this.out = out; 
  }

  public Funnel(NrpMachine machine,String left,
                                String right,String out)
  { 
    this.left = machine.getChannel(left); 
    this.right = machine.getChannel(right); 
    this.out = machine.getChannel(out); 
    machine.add(this);
  }

 final public String toString(){ 
    return "funnel(" + out + "," + left + "," + right + ")";
  }

  protected byte activation(Machine machine)
  {
    Channel in = fromLeft ? left : right;
    byte b = fix(in,machine);
    if (b == TERM){
      put(out,in.get(),machine);
      b = STOP;
    }
    if (b != SUSP) fromLeft = !fromLeft;
    return b;
  }
}

Two points are important to note:

• Funnel does not remain for ever stuck on an empty input channel;
• emptyness of an input channel (when fix returns STOP) cannot be decided before the end of the current instant, so switching to the opposite input channel can only take place at next instant.