pthreads - Xlib Muti-thread program only works under strace -


i'm writing muti-thread program using xlib, pthread , cairo. program create thread in order draw ten points after click event.

the problem is:

after program drew 3 points, got crashed , xlib complaint 

x error of failed request:  badrequest (invalid request code or no such operation)   major opcode of failed request:  0 ()   serial number of failed request:  67   current serial number in output stream:  97

however, can work when i'm using strace "strace ./a.out".

here's code-clips:

void *draw_point(void *arg) { //paint random-postion point     int = 0;     int seed;     double x ,y;     srand(seed);     cairo_set_source_rgba (cairo, 1, 0.2, 0.2, 0.6);     for(i = 0; i< 10; i++) {         x = rand() % 200;         y = rand() % 200;         if(candraw) {             cairo_arc (cairo, x, y, 10.0, 0, 2*m_pi);             cairo_fill (cairo);         }         hasdraw = true;         sleep(1);     }     return null; }  bool win_main(void) {     int clickx = 0, clicky = 0;     unsigned long valuemask;     xevent event;      valuemask = buttonpressmask | buttonreleasemask | buttonmotionmask | pointermotionmask;      xselectinput(display, win, valuemask);      pthread_t thread;      while (1) {         while (xpending(display) == 0) {             candraw = true;             if(hasdraw)             xflush(display);             candraw = false;         }         xnextevent(display, &event);         candraw = false;         switch (event.type) {         case motionnotify:             //...             break;         case buttonpress:             clickx = event.xbutton.x;             clicky = event.xbutton.y;             if(clicky < 50)                 pthread_create(&thread, null, draw_point, null);             break;         case buttonrelease:             //...             break;         default:             break;         }     }     return 0; }

does has idea weird problem? lot!

the problem caused using multi-threading 2 threads trying access display @ same.

strace change timing, threads accessing display @ different times.

xlib have functions prevent conflict. lookup xinitthreads, enables thread support , xlockdisplay , xunlockdisplay, need call each thread before , after accessing display.


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