interface iclaim
{
  in bool claim ();
  in void release ();
  behavior
  {
    bool claimed = false;
    on claim: {claimed = true; reply (true);}
    on claim: {claimed = false; reply (false);}
    [claimed] on release: claimed = false;
  }
}

component claim
{
  provides iclaim left;
  provides iclaim right;
  behavior
  {
    on left.claim (), right.claim (): reply (!left.claimed && !right.claimed);
    on left.release (), right.release (): {}
  }
}

interface iclient
{
  in bool start ();
  in void stop ();
  behavior
  {
    bool idle = true;
    [idle] on start: {idle = false; reply (true);}
    [idle] on start: reply (false);
    [!idle] on stop: idle = true;
  }
}

component user
{
  provides iclient client;
  requires iclaim resource;
  behavior
  {
    on client.start (): reply (resource.claim ());
    on client.stop (): resource.release ();
  }
}

component shared_resource
{
  provides iclient left;
  provides iclient right;
  system
  {
    user user1;
    user user2;
    claim resource;
    left <=> user1.client;
    right <=> user2.client;
    resource.left <=> user1.resource;
    resource.right <=> user2.resource;
  }
}