c - sdl2 drawing from separate threads on Linux vs Windows -

i have simple drawing going on sdl2 working under windows i've ported on linux, isn't drawing different threads i've spawned.

i'm controlling access renderer using mutex's.

the functions process , output logging expected, thing doesn't appear working renderer never updates display under linux.

if comment out the threading, , run function main expected result. code hasn't changed between linux , windows versions.

the code compiles without warnings under -wall , -pedantic. since i've started compiling linux i've added -pthread flag in case required (hasn't made difference).

if aware of gotchas or might have inkling why isn't working doing me enormous favour.

        static int thread_processing(void* data)      {         srand(time(null));      //randomize           threaddata *td = data;           bucket *bucket;          int b_id = -1;          color threadcolor;         //unique color each respective thread         color_randomize(&threadcolor);         threadcolor.a = 255;          fprintf(stderr, "%d buckets process..\n", td->barray->size);         while (1) {             //check there buckets left process             if (td->barray->rendered >= td->barray->size)                 break;              //acquie/lock access bucket array             sdl_lockmutex(td->b_mutex);              //retrieve buucket id process             b_id = td->barray->rendered;             td->barray->rendered++;              fprintf(stderr, "rendering bucket: %d\n", b_id);             //release access bucket array             sdl_unlockmutex(td->b_mutex);              //retrieve addr of bucket process             bucket = &(td->barray->buckets[b_id]);              //lock access renderer             sdl_lockmutex(td->r_mutex);              //draw rect on screen bucket processed             draw_bucketoutline(td->renderer, bucket, &threadcolor);             sdl_renderpresent(td->renderer);              //release access renderer object             sdl_unlockmutex(td->r_mutex);              //process bucket             process_bucket(td->scene, bucket);              //acquire/lock acess renderer object             sdl_lockmutex(td->r_mutex);              //draw processed data ot screen             draw_bucket(td->renderer, bucket);             sdl_renderpresent(td->renderer);              //release access renderer object             sdl_unlockmutex(td->r_mutex);         }          return 0;     }      void draw_bucketoutline(sdl_renderer *renderer, bucket *b, color *color) {     //set colour of outline     sdl_setrenderdrawcolor(renderer, 125, 125, 125, 255);      //set outline position     sdl_rect rect;     rect.w = b->resolution.width;     rect.h = b->resolution.height;     rect.x = b->start.x;     rect.y = b->start.y;      //draw outline     sdl_renderdrawrect(renderer, &rect);      //crop rectangle inwards filling inside of outline     rect.w -= 2;     rect.h -= 2;     rect.x += 1;     rect.y += 1;      //set colour fill area     sdl_setrenderdrawcolor(renderer, color->r, color->g, color->b, color->a);      //draw fill area     sdl_renderfillrect(renderer, &rect); } 

main.....

//iterate on threads, processing int t; (t = 0; t < thread_count; t++) {     threads[t] = sdl_createthread(thread_processing, null, &td); }  //iterate on threads, clean them (t = 0; t < thread_count; t++) {     int status;     sdl_waitthread(threads[t], &status); } 

compiling

gcc -wall -pedantic -lm -i/usr/include/sdl2 -d_reentrant -lx11 -pthread raytracer.c -lsdl2 -o raytracer 

sdl2 on linux uses opengl accelerated rendering (it defaults d3d acceleration on windows), , opengl have thread-local context. cannot use same gl context in separate threads. have render in single thread, e.g. putting rendering commands in queue , replaying them in rendering thread. , shouldn't have used multiple rendering threads in first place.