Allegro 5 and shared_ptr: Crash on exit

no-reply@allegro.cc (Fishcake) — Sun, 16 Dec 2012 18:03:33 +0000

Anyone can figure out why this is crashing on exit (EXC_BAD_ACCESS)?

#SelectExpand
  1Application::Application() {
  2    
  3}
  4
  5Application::~Application() {
  6    
  7    al_destroy_timer(timer);
  8    al_destroy_event_queue(eventQueue);
  9    al_destroy_display(display);
 10    al_uninstall_system();
 11    
 12}
 13
 14void Application::init(int                argc,
 15                       char               **argv,
 16                       const std::string  &configFilename) {
 17    /* Initialize Allegro and everything */
 18}
 19
 20int Application::run() {
 21    
 22    bool shouldExit = false;
 23    al_start_timer(timer);
 24    
 25    while (!shouldExit && gameStateManager->getActiveStateCount() > 0) {
 26       /* Do stuff */
 27    }
 28
 29    al_stop_timer(timer);
 30    
 31    return 0;
 32}
 33
 34// ApplicationPtr is a typedef of std::shared_ptr
 35// This is probably a bad way of doing singleton, but heck,
 36// I'm rushing for Santahack!
 37ApplicationPtr Application::GetInstance() {
 38    static ApplicationPtr application = std::make_shared<Application>();
 39    return application;
 40}

#include 
#include "Application.h"

int main(int argc, char **argv) {
    
    ApplicationPtr app = Application::GetInstance();
    app->init(argc, argv, "data/config.ini");
    app->run();
    
    return 0;
    
}

I don't know how to get the stack trace in Xcode, so here's a screenshot of it instead.

{"name":"607036","src":"\/\/djungxnpq2nug.cloudfront.net\/image\/cache\/7\/9\/79870dd1522dad465e4890e48735dccc.png","w":339,"h":500,"tn":"\/\/djungxnpq2nug.cloudfront.net\/image\/cache\/7\/9\/79870dd1522dad465e4890e48735dccc"}

This is my first time using smart pointers.

no-reply@allegro.cc (Elias) — Sun, 16 Dec 2012 18:19:20 +0000

My guess is you call Allegro functions after shutting down Allegro. By default Allegro gets shut down at the end of the main() function, but global destructors are called afterwards.

You could use al_install_system instead of al_init and pass your own atexit function to prevent the automatic shutdown at the end of main().

no-reply@allegro.cc (Kris Asick) — Sun, 16 Dec 2012 19:36:11 +0000

Elias has got it right. If you want to continue making your program the way you are, you need to explicitly create and destroy your Application object in your main() procedure like this:

Application *myapp = new Application;

// Do Stuff

delete myapp;

This way, Allegro won't auto-shutdown after main() returns before your Application objects are destroyed. ALL objects with Allegro functions in them MUST be created explicitly for this reason.

no-reply@allegro.cc (Fishcake) — Sun, 16 Dec 2012 19:42:51 +0000

Yes, you're right. I fixed it by using al_install_system, passing a dummy function as the second argument.

// I'm dumb!
int DummyExitFunction(void (*stuff)(void)) {
    return 0;
}

//...

al_install_system(ALLEGRO_VERSION_INT, DummyExitFunction);

I still don't get why the function needs to have that weird signature instead of just void (*)(void). But who cares for now, as long as it works! Thanks!

no-reply@allegro.cc (Kris Asick) — Sun, 16 Dec 2012 19:51:47 +0000

One big catch you may run into with your current approach is the order in which your objects are removed from memory, specifically if you place Allegro code into the destructors of even more implicitly declared objects. In this event, the order in which you create your objects will be important so that the one that actually shuts down Allegro in its destructor will be called last when your program exits.

Overall, it's still safer to explicitly declare any objects that have Allegro functions in their destructors.