DiscardCtrl causes general protection fault

[gdargaud]

Hello all,

I just stumbled upon a problem that seems too simple to be true. If I call DiscardCtrl from _that_ control callback, or if I call it from the panel callback without swallowing the even, I get a general protection fault.

Here's an example. To test it, double click on the control and it crashes. If you double click on the panel or use "return 1", no problem:

#include <cvirte.h>
#include <utility.h>
static int CtrlSlide=0, StyleIndex=-1;

static int AuthorizedStyles[]={        // Should work on all of those
        CTRL_NUMERIC_THERMOMETER,
        CTRL_NUMERIC_TANK,
        CTRL_NUMERIC_GAUGE,
        CTRL_NUMERIC_METER,
        CTRL_NUMERIC_KNOB,
        CTRL_NUMERIC_DIAL,
        CTRL_NUMERIC_VSLIDE,
        CTRL_NUMERIC_HSLIDE,
        CTRL_NUMERIC_FLAT_VSLIDE,
        CTRL_NUMERIC_FLAT_HSLIDE,
        CTRL_NUMERIC_LEVEL_VSLIDE,
        CTRL_NUMERIC_LEVEL_HSLIDE,
        CTRL_NUMERIC_POINTER_VSLIDE,
        CTRL_NUMERIC_POINTER_HSLIDE,
        CTRL_NUMERIC_THERMOMETER_LS,
        CTRL_NUMERIC_TANK_LS,
        CTRL_NUMERIC_GAUGE_LS,
        CTRL_NUMERIC_METER_LS,
        CTRL_NUMERIC_KNOB_LS,
        CTRL_NUMERIC_DIAL_LS,
        CTRL_NUMERIC_LEVEL_VSLIDE_LS,
        CTRL_NUMERIC_LEVEL_HSLIDE_LS,
        CTRL_NUMERIC_POINTER_VSLIDE_LS,
        CTRL_NUMERIC_POINTER_HSLIDE_LS
};

static char* StrStyles[]={
        "THERMOMETER",
        "TANK",
        "GAUGE",
        "METER",
        "KNOB",
        "DIAL",
        "VSLIDE",
        "HSLIDE",
        "FLAT_VSLIDE",
        "FLAT_HSLIDE",
        "LEVEL_VSLIDE",
        "LEVEL_HSLIDE",
        "POINTER_VSLIDE",
        "POINTER_HSLIDE",
        "THERMOMETER_LS",
        "TANK_LS",
        "GAUGE_LS",
        "METER_LS",
        "KNOB_LS",
        "DIAL_LS",
        "LEVEL_VSLIDE_LS",
        "LEVEL_HSLIDE_LS",
        "POINTER_VSLIDE_LS",
        "POINTER_HSLIDE_LS"
};

	
int CVICALLBACK cb_TestSRP (int panel, int control, int event,
		void *callbackData, int eventData1, int eventData2) {
	switch (event) {
		case EVENT_RIGHT_CLICK: DoSomething(panel, control); break;
	}
	return 0;
}

int CVICALLBACK cb_QuitSRP (int panel, int control, int event,
		void *callbackData, int eventData1, int eventData2) {
	switch (event) {
		case EVENT_COMMIT: QuitUserInterface (0); break;
	}
	return 0;
}

int CVICALLBACK cbp_Change(int panel, int event,
		void *callbackData, int eventData1, int eventData2) {
	switch (event) {
		case EVENT_LEFT_DOUBLE_CLICK:
			if (CtrlSlide!=0) DiscardCtrl (panel, CtrlSlide);
			CtrlSlide = NewCtrl (panel, AuthorizedStyles[(++StyleIndex)%(sizeof(AuthorizedStyles)/4)], "", 50, 80);
			SetCtrlAttribute (panel, CtrlSlide, ATTR_CALLBACK_FUNCTION_POINTER, cb_TestSRP);
			SetCtrlAttribute (panel, CtrlSlide, ATTR_LABEL_TEXT, StrStyles[StyleIndex%(sizeof(AuthorizedStyles)/4)]);
			return 0; // Change it to 1 and there's no problem
	}
	return 0;
}

int main (int argc, char *argv[]) {
	if (InitCVIRTE (0, argv, 0) == 0)  return -1;    /* out of memory */
	
	int Pnl = NewPanel (0, "Test slide popup", 100, 100, 300, 300);

	int CtrlQuit= NewCtrl (Pnl, CTRL_ROUNDED_COMMAND_BUTTON, "QUIT", 0, 0);
	SetCtrlAttribute (Pnl, CtrlQuit, ATTR_VISIBLE, 0);
	SetCtrlAttribute (Pnl, CtrlQuit, ATTR_CALLBACK_FUNCTION_POINTER, cb_QuitSRP);
	SetPanelAttribute(Pnl, ATTR_CLOSE_CTRL, CtrlQuit);
	SetPanelAttribute(Pnl, ATTR_CALLBACK_FUNCTION_POINTER, cbp_Change);
	
	cbp_Change(Pnl, EVENT_LEFT_DOUBLE_CLICK, NULL, 0, 0);
	
	DisplayPanel(Pnl);
	RunUserInterface();
	return 0;
}

[Wolfgang · Accepted solution]

The problem can be 'solved' reading the help :

You cannot discard a control in the callback function for the control, except when responding to the EVENT_COMMIT event. Discarding the control from its own callback function in response to other events might cause unpredictable behavior.

[OVR_CZ]

You may try use PostDeferredCall function for this purpose

[gdargaud]

OK, I wasn't too surprised about the control callback crash, but a little bit more when it happened in the panel callback...