Using Application Handlers

In the Boost.Application, the 'aspects handlers' is the way that you can define a custom action to response some events, that are initiated by user via SCM or SIGNALS.

Table 1.4. Pre-configured Handlers available in the library

Aspect Name	Aspect Contract Class	Aspect Final Class	Aspect Functionality
pause_handler	pause_handler	pause_handler_default_behaviour	When 'pause' event is detected, fire a user defined callback
resume_handler	resume_handler	resume_handler_default_behaviour	When 'resume' event is detected, fire a user defined callback
termination_handler	termination_handler	termination_handler_default_behaviour	When 'stop' signal/event is detected, fire a user defined callback
limit_single_instance	limit_single_instance	limit_single_instance_default_behaviour	When single instance feature is enabled, fire a user defined callback to handle it

The user can define the handler like this:

bool stop(void)

Note that handlers must return a 'bool' to indicate to 'application mode engine', what action need be done, e.g.:

class myapp
{
public:
// ...
bool stop()
{
   char type;
   do
   {
      std::cout << "Do you want to exit? [y/n]" << std::endl;
      std::cin >> type;
   }
   while( !std::cin.fail() && type!='y' && type!='n' );

   if(type == 'y')
   {
      // return true to tell to the 'application mode engine' to stop application.
      // This implies:
      // 1. The 'application mode engine' will set the 'application 'status' aspect to status::stopped;
      // 2. The 'application mode engine' will signalize the 'application 'wait_for_termination_request' aspect to release.
      return true;
   }

   // tell the 'application mode engine' to continue application (ignore requisited action)
   return false;
}
// ...
};