[cairo] memory problem with the X11 - SHM backend

Cedric Roux sed at free.fr
Sat Nov 30 16:06:53 PST 2013

Hi cairo,

I have a problem running you with X11/Xshm. This is a debian host here.
The following program reports an always increasing "evs" thing.
The first line it outputs is "1 evs" and the last one is
"7409 evs". That means the X event queue is not emptied. (Please don't
look at the style, it's a quick and dirty hack to let the problem pop

Oh yes, you need to create a 128x128 mini.png file to run it. Content
does not seem to matter, I have a white image here.

Am I doing something wrong with you or is the problem on your side?
If I call XSync(d, True) the queue is emptied and the original program
that exhibited the problem and from which I wrote that little proof of
concept still works pretty reasonably well. (What a terrific sentence
I just wrote...)
Except it smokes my CPU like hell, but that's none of your concern I

In the hope that you can help me here...
Regards cairo, have a nice sunday.

#include <stdio.h>
#include <cairo/cairo.h>
#include <cairo/cairo-xlib.h>
#include <X11/Xlib.h>
#include <stdlib.h>

int main(void)
   cairo_surface_t *image;
   cairo_pattern_t *pletters;
   cairo_surface_t *cs;
   Display *d;
   Pixmap p;

   d = XOpenDisplay(0); if (!d) abort();
   p = XCreatePixmap(d, DefaultRootWindow(d), 256, 256,
                     DefaultDepth(d, DefaultScreen(d)));
   cs = cairo_xlib_surface_create(d, p, DefaultVisual(d, DefaultScreen(d)),
                                  256, 256);

   //image = cairo_image_surface_create(CAIRO_FORMAT_ARGB32, 512, 512);
   image = cairo_image_surface_create_from_png("mini.png");
   pletters = cairo_pattern_create_for_surface(image);

   int y;
   for (y=0; y < 500; y++) {
     int i;
     cairo_matrix_t m;
     cairo_t *c = cairo_create(cs);

     //cairo_scale(c, 0.5, 0.5);
     //cairo_translate(c, 1, 1);
     for (i = 0; i < 15; i++) {
       //static int z = 2;  cairo_matrix_init_translate(&m, 0, 0); //z = 
2 - z;
       cairo_matrix_init_translate(&m, 0, 0); //z = 2 - z;
       cairo_pattern_set_matrix(pletters, &m);
       cairo_set_source(c, pletters);

       //XSync(d, True);
       printf("%d evs\n", XEventsQueued(d, QueuedAfterReading));

       XEvent ev; while (XCheckMaskEvent(d, -1L, &ev)) { 
printf("event!\n"); }


   return 0;

More information about the cairo mailing list