SDL and X11 multithreading Fatal IO Error

Question

I'm trying to create a simple multithreading example using C++ and SDL as shown here:

#include <iostream>
#include "SDL/SDL_image.h"
#include "SDL/SDL.h"
#include "SDL/SDL_thread.h"
#include "X11/Xlib.h"
#include "SDLAbstractionLayer.h"
#include <string>

using namespace std;

SDL_Thread* thread = NULL;
bool quit = false;

int myThread(void* data) {
   while (!quit) {
      //caption animation
      SDL_WM_SetCaption ("Thread is running", NULL);
      SDL_Delay(250);

      SDL_WM_SetCaption("Thread is running.", NULL);
      SDL_Delay(250);

      SDL_WM_SetCaption("Thread is running..", NULL);
      SDL_Delay(250);

      SDL_WM_SetCaption("Thread is running...", NULL);
      SDL_Delay(250);
   }

   return 0;
}

int main(int argc, char* argv[]) {
   SDL_Surface* screen = init(640, 480, "");
   XInitThreads();

   Surface test("resources/image.png");
   thread = SDL_CreateThread(myThread, NULL);
   SDL_Event event;

   while (!quit) {
      if(SDL_PollEvent(&event)) {
         if (event.type == SDL_QUIT) {
            quit = true;
            break;
         }

         fillScreen(screen, Surface::WHITE);
         applySurface(0, 0, test, screen);
         flip(screen);
      }
   }

   cleanUp();
   SDL_KillThread(thread);

   return 0;
}

The problem is that when I run it in Eclipse or in the terminal, I get this message:

XIO:  fatal IO error 0 (Success) on X server ":0.0"
  after 113 requests (113 known processed) with 0 events remaining.

or this one:

XIO:  fatal IO error 11 (Resource temporarily unavailable) on X server ":0.0"
  after 113 requests (113 known processed) with 2 events remaining.

I'm using Ubuntu 13 with Eclipse Kepler. I've tried to do some research, but wasn't able to find anything useful.

Edit: So I updated the code to include a counter and a few cout's all over the place:

int myThread(void* data) {
   while (!quit) {
      //caption animation
      SDL_WM_SetCaption ("Thread is running", NULL);
      SDL_Delay(250);

      cout << "Thread is running 1" << endl;

      SDL_WM_SetCaption("Thread is running.", NULL);
      SDL_Delay(250);

      cout << "Thread is running 2" << endl;

      SDL_WM_SetCaption("Thread is running..", NULL);
      SDL_Delay(250);

      cout << "Thread is running 3" << endl;

      SDL_WM_SetCaption("Thread is running...", NULL);
      SDL_Delay(250);

      cout << "Thread is running 4" << endl;
   }

   return 0;
}

int main(int argc, char* argv[]) {
   SDL_Surface* screen = init(640, 480, "");
   XInitThreads();

   Surface test("resources/image.png");
   thread = SDL_CreateThread(myThread, NULL);
   SDL_Event event;
   int count = 1;

   while (!quit) {
      if(SDL_PollEvent(&event)) {
         if (event.type == SDL_QUIT) {
            quit = true;
            break;
         }

         fillScreen(screen, Surface::WHITE);
         applySurface(0, 0, test, screen);
         flip(screen);

         cout << "finished iteration " << count++ << endl;
      }
   }

and here's the output from the console after running it once:

finished iteration 1
Thread is running 1
XIO:  fatal IO error 0 (Success) on X server ":0.0"
      after 113 requests (113 known processed) with 0 events remaining.

then, after running it a second time:

finished iteration 1
finished iteration 2
Thread is running 1
Thread is running 2
XIO:  fatal IO error 0 (Success) on X server ":0.0"
      after 116 requests (116 known processed) with 0 events remaining.

Answer 1

When in doubt do all SDL operations on the main thread.

The primary exception is SDL_PostEvent() .

Answer 2

Ah never mind. I just got a reply from an email I sent to the person who made the tutorial I'm following:

Yeah that's bug in my application which I am fixing the in the SDL 2.0 tutorial. Check out the SDL 2.0 multithreading example for a fix. The problem is that SDL having multiple threads do rendering doesn't work. So setting the caption from a another thread doesn't work right. In the 2.0 tutorial, rendering is in one thread and console output is in another.