Indirect blocking out event (Dezyne Reference Manual)

5.7 Indirect blocking out event

The in-event on the provides port (p.a) blocks (does not return) until a reply is handled. This happens in the handling of the requires port out-event (r.b). Also see blocking.

interface I
{
  in void a ();
  out void b ();
  behavior
  {
    on a: b;
  }
}

interface I2
{
   in void a ();
   out void b ();
   behavior
   {
     bool idle = true;
     [idle] on a: idle = false;
     [!idle] on a: illegal;
     [!idle] on inevitable: {idle = true; b;}
   }
}

component indirect_blocking_out
{
  provides blocking I p;
  requires I2 r;
  behavior
  {
    blocking on p.a (): r.a ();
    on r.b (): {p.b (); p.reply ();}
  }
}

If the keyword blocking in above example would be omitted it would lead to an erroneous situation since the provides in-event (p.a) would return before the provides out-event (p.b) would have been generated.