struct FixedBuf {
   FixedBuf (int sz) : pos(0), size(sz), buf((byte*)malloc(size)) {}
   ~FixedBuf () { free(buf); }
   int pos;
   int size;
   byte *buf;
};

cairo_status_t writer (void *closure, const unsigned char *data, unsigned int length)
{
   FixedBuf &buf = *(FixedBuf*)closure;
   if (buf.pos + (int)length >= buf.size)
      return CAIRO_STATUS_WRITE_ERROR;
   for (int i = 0; i < (int)length; ++i)
      buf.buf[buf.pos++] = (byte)data[i];
   return CAIRO_STATUS_SUCCESS;
}

#define NLETTERS 10      
double fontSize[NLETTERS][NLETTERS];
void initFontSizes () {
   for (int j = 0; j < NLETTERS; ++j)
      for (int i = 0; i < NLETTERS; ++i)
         fontSize[j][i] = floorf(10 * (20 + (10.0f * rand() / RAND_MAX)) / 10);
}

THREAD_RET THREAD_MOD runPure(void *param) {
   osMutexLock(&g_mutex);
   int id = (int)threadId++;
   osMutexUnlock(&g_mutex);
   char buf[1024];
   const char* symbols[] = {"a", "b", "c", "d", "e", "f", "g", "h"};
   int sz = 600;
   FixedBuf fb(16000);
   for (int i = 0; i < 20; ++i) {
      cairo_surface_t *surface;
      cairo_t *cr;
      surface = cairo_image_surface_create (CAIRO_FORMAT_ARGB32, 400, 400);
      cr = cairo_create(surface);

      cairo_set_source_rgb(cr, 0, 0, 0);

      for (int j = 0; j < NLETTERS; ++j) {
         for (int i = 0; i < NLETTERS; ++i) {
            cairo_move_to(cr, (i+1) * sz / (NLETTERS + 1), (j+1) * sz / (NLETTERS + 1));
            cairo_select_font_face(cr, "Arial", CAIRO_FONT_SLANT_NORMAL, CAIRO_FONT_WEIGHT_NORMAL);
            cairo_set_font_size(cr, fontSize[j][i]);
            cairo_show_text(cr, symbols[(i + j) % NELEM(symbols)]);   
         }
      }

      cairo_surface_write_to_png_stream(surface, writer, &fb);
      int len = fb.pos;
      int h = hash(fb.buf, len);
      printf("%i: %i\n", id, len);
      sprintf(buf, "png/%i_%lu.png", len, h);
      osMutexLock(&g_mutex);
      if (!g_map.find(buf)) {
         g_map.insert(buf, 1);
         FileOutput fo(buf);
         fo.write(fb.buf, len);
         fo.flush();
      }             
      osMutexUnlock(&g_mutex);
      fb.pos = 0;
   }
   return 0;
}

#define NUM 4

void TestConcurrent () {
   initFontSizes();
   osMutexCreate(&g_mutex);
   for (int i = 0; i < NUM; ++i) {
      osThreadCreate(runPure, NULL); 
   }
}