SDL mutex example

   1 #define WORK_AMOUNT 5
   2 
   3 #include <stdio.h>
   4 #include <stdlib.h>
   5 #include "SDL.h"
   6 #include "SDL_thread.h"
   7 
   8 // Global variables
   9 SDL_mutex* console_mutex;
  10 SDL_Thread* thread1;
  11 SDL_Thread* thread2;
  12 
  13 /*
  14 This string-printing routine is thread-safe. The delaying makes it possible for a human
  15 reader to see what's going on during program execution.
  16 Try commenting out the Lock/Unlock rows and see what happens.
  17 */
  18 void safePrintStr(char* str)
  19 {
  20     /*
  21     Make sure only one thread at a time gets access to the lines 
  22     between Lock/Unlock (also known as a critical region)
  23     */
  24     SDL_LockMutex(console_mutex);
  25 
  26     int i;
  27     for(i = 0; str[i]; ++i) {
  28         printf("%c", str[i]);
  29         SDL_Delay(10);
  30     }
  31 
  32     // Release the lock
  33     SDL_UnlockMutex(console_mutex);
  34 }
  35 
  36 
  37 // This is the routine that embodies a worker thread
  38 int printer(void* data)
  39 {
  40     // Start with identifying myself.
  41     char* name = (char*)data;
  42     char buf[80];
  43     sprintf(buf, "Worker '%s' started.\n", name);
  44     safePrintStr(buf);
  45 
  46     // Make sure workers work at different paces
  47     int pace;
  48     if (name[0] == 'A')
  49         pace = 1000;
  50     if (name[0] == 'B')
  51         pace = 2500;
  52 
  53     // This loop does the work
  54     int workLeft = WORK_AMOUNT;
  55     while (workLeft > 0) {
  56         // Display a message before every step of work I do.
  57         int step = 1+WORK_AMOUNT-workLeft;
  58         int percent = 100 * step / WORK_AMOUNT;
  59         sprintf(buf, "Worker '%s' is doing step %d of %d (%d%% finished).\n", name, step, WORK_AMOUNT, percent);
  60         safePrintStr(buf);
  61 
  62         // Do my work...
  63         workLeft--;
  64         SDL_Delay(pace);
  65     }
  66 
  67     // I'm done!
  68     sprintf(buf, "Worker '%s' is done.\n", name);
  69     safePrintStr(buf);
  70 
  71     return 0;
  72 }
  73 
  74 
  75 // Boot-up code
  76 void init()
  77 {
  78     SDL_Init(0);
  79     console_mutex = SDL_CreateMutex();
  80 }
  81 
  82 
  83 // Shut-down code
  84 void quit()
  85 {
  86     SDL_DestroyMutex(console_mutex);
  87     SDL_Quit();
  88 }
  89 
  90 
  91 // Program entry point
  92 int main(int argc, char* argv[])
  93 {
  94     init();
  95 
  96     // Run the two worker threads
  97     // Note: it can be necessary to add (void*) before "Alpha" and "Beta"
  98     // else this error apears: invalid conversion from 'const void*' to 'void*'
  99     thread1 = SDL_CreateThread(printer, "Alpha");
 100     thread2 = SDL_CreateThread(printer, "Beta"); 
 101 
 102     // The main thread is put to sleep until both worker threads are done.
 103     SDL_WaitThread(thread1, NULL);
 104     SDL_WaitThread(thread2, NULL);
 105 
 106     // Note: we don't have to use safePrintStr here since
 107     // we're the only thread active.
 108     printf("Main thread has done its waiting, now quit.\n");
 109     quit();
 110 
 111     return 0;
 112 }