# Receives the callback from system when a given signal arise
interface SignalHandler
	# Invoked after a call to `check_signals` if a signal has been raised
	# (should be redefed by subclasses)
	#
	# Should be used by most signals except `sigkill` and `sigstop` since they
	# cannot be caught, blocked or ignored.
	#
	#     class MyReceiver
	#         super SignalHandler
	#
	#         redef fun receive_signal(signal) do print "received safely {signal}"
	#     end
	#
	#     var r = new MyReceiver
	#     r.handle_signal(sigint, true) # will call back when "check_signals" is called
	#     # ...
	#     check_signals # if a signal was received, it will invoke `r.receive_signal`
	fun receive_signal(signal: Int) do end

	# Called immediatly on receiving an unsafe signal (should be redefed by subclasses)
	#
	# Should be used for `sigkill` and `sigstop` since they cannot be caught,
	# blocked or ignored.
	#
	# You should consider this methods as being fragile. It should be implemented in C
	# and you should not do too much callbacks to Nit.
	#
	#     class MyReceiver
	#         super SignalHandler
	#
	#         redef fun receive_signal_unsafe(signal) do print "received unsafely {signal}"
	#     end
	#
	#     var r = new MyReceiver
	#     r.handle_signal(sigsegv, false) # `r.receive_signal_unsafe` will be invoked on sigsegv
	fun receive_signal_unsafe(signal: Int) do end

	# Set the receiver as the handler of the signal
	#
	# If `safely`, receiver will be called when `check_signals` in invoked
	# otherwise the receiver is invoked when the signal is raised, it may
	# crash the Nit system but is unavoidable for unstoppable signals.
	fun handle_signal(signal: Int, safely: Bool) import receive_signal `{
		if (signal < 32 && signal >=0) {
			struct sigaction act;
			sigemptyset(&act.sa_mask);
			act.sa_flags = 0;
			act.sa_handler = receiver;

			sigaction(signal, &act, NULL);

		#ifdef SignalHandler_decr_ref
			SignalHandler last_handler = (SignalHandler)nit_signals_list[signal].handler;
			if (last_handler != NULL)
				SignalHandler_decr_ref(last_handler);
		#endif

			nit_signals_list[signal].handler = self;

		#ifdef SignalHandler_incr_ref
			SignalHandler_incr_ref(self);
		#endif

			nit_signals_list[signal].safely = safely;

			nit_SignalHandler_receive_signal =
				(void (*)(void*, long))&SignalHandler_receive_signal;
		}
	`}

	# Set to ignore the signal
	fun ignore_signal(signal: Int) `{
		if (signal < 32 && signal >=0) {
			struct sigaction act;
			sigemptyset(&act.sa_mask);
			act.sa_flags = 0;
			act.sa_handler = SIG_IGN;
			sigaction(signal, &act, NULL);

		#ifdef SignalHandler_decr_ref
			SignalHandler last_handler = (SignalHandler)nit_signals_list[signal].handler;
			if (last_handler != NULL)
				SignalHandler_decr_ref(last_handler);
		#endif
		}
	`}

	# Set default action for the signal
	fun default_signal(signal: Int) `{
		if (signal < 32 && signal >=0) {
			struct sigaction act;
			sigemptyset(&act.sa_mask);
			act.sa_flags = 0;
			act.sa_handler = SIG_DFL;
			sigaction(signal, &act, NULL);

		#ifdef SignalHandler_decr_ref
			SignalHandler last_handler = (SignalHandler)nit_signals_list[signal].handler;
			if (last_handler != NULL)
				SignalHandler_decr_ref(last_handler);
		#endif
		}
	`}
end