Remove almost all instances of "volatile" keyword.

As Tiffany pointed out in Bugzilla, volatile is not useful for thread safety:

https://software.intel.com/en-us/blogs/2007/11/30/volatile-almost-useless-for-multi-threaded-programming/

Some of these volatiles didn't need to be, some were otherwise protected by
spinlocks or mutexes, and some got moved over to SDL_atomic_t data, etc.

Fixes Bugzilla #3220.

test/testatomic.c

@@ -284,7 +284,7 @@ typedef struct
     char cache_pad4[SDL_CACHELINE_SIZE-sizeof(SDL_SpinLock)-2*sizeof(SDL_atomic_t)];
 #endif
 
-    volatile SDL_bool active;
+    SDL_atomic_t active;
 
     /* Only needed for the mutex test */
     SDL_mutex *mutex;
@@ -305,7 +305,7 @@ static void InitEventQueue(SDL_EventQueue *queue)
     SDL_AtomicSet(&queue->rwcount, 0);
     SDL_AtomicSet(&queue->watcher, 0);
 #endif
-    queue->active = SDL_TRUE;
+    SDL_AtomicSet(&queue->active, 1);
 }
 
 static SDL_bool EnqueueEvent_LockFree(SDL_EventQueue *queue, const SDL_Event *event)
@@ -538,7 +538,7 @@ static int FIFO_Reader(void* _data)
             if (DequeueEvent_LockFree(queue, &event)) {
                 WriterData *writer = (WriterData*)event.user.data1;
                 ++data->counters[writer->index];
-            } else if (queue->active) {
+            } else if (SDL_AtomicGet(&queue->active)) {
                 ++data->waits;
                 SDL_Delay(0);
             } else {
@@ -551,7 +551,7 @@ static int FIFO_Reader(void* _data)
             if (DequeueEvent_Mutex(queue, &event)) {
                 WriterData *writer = (WriterData*)event.user.data1;
                 ++data->counters[writer->index];
-            } else if (queue->active) {
+            } else if (SDL_AtomicGet(&queue->active)) {
                 ++data->waits;
                 SDL_Delay(0);
             } else {
@@ -571,7 +571,7 @@ static int FIFO_Watcher(void* _data)
 {
     SDL_EventQueue *queue = (SDL_EventQueue *)_data;
 
-    while (queue->active) {
+    while (SDL_AtomicGet(&queue->active)) {
         SDL_AtomicLock(&queue->lock);
         SDL_AtomicIncRef(&queue->watcher);
         while (SDL_AtomicGet(&queue->rwcount) > 0) {
@@ -652,7 +652,7 @@ static void RunFIFOTest(SDL_bool lock_free)
     }
 
     /* Shut down the queue so readers exit */
-    queue.active = SDL_FALSE;
+    SDL_AtomicSet(&queue.active, 0);
 
     /* Wait for the readers */
     while (SDL_AtomicGet(&readersRunning) > 0) {

test/testlock.c

@@ -23,7 +23,7 @@
 static SDL_mutex *mutex = NULL;
 static SDL_threadID mainthread;
 static SDL_Thread *threads[6];
-static volatile int doterminate = 0;
+static SDL_atomic_t doterminate;
 
 /*
  * SDL_Quit() shouldn't be used with atexit() directly because
@@ -45,7 +45,7 @@ void
 terminate(int sig)
 {
     signal(SIGINT, terminate);
-    doterminate = 1;
+    SDL_AtomicSet(&doterminate, 1);
 }
 
 void
@@ -54,7 +54,7 @@ closemutex(int sig)
     SDL_threadID id = SDL_ThreadID();
     int i;
     SDL_Log("Process %lu:  Cleaning up...\n", id == mainthread ? 0 : id);
-    doterminate = 1;
+    SDL_AtomicSet(&doterminate, 1);
     for (i = 0; i < 6; ++i)
         SDL_WaitThread(threads[i], NULL);
     SDL_DestroyMutex(mutex);
@@ -66,7 +66,7 @@ Run(void *data)
 {
     if (SDL_ThreadID() == mainthread)
         signal(SIGTERM, closemutex);
-    while (!doterminate) {
+    while (!SDL_AtomicGet(&doterminate)) {
         SDL_Log("Process %lu ready to work\n", SDL_ThreadID());
         if (SDL_LockMutex(mutex) < 0) {
             SDL_LogError(SDL_LOG_CATEGORY_APPLICATION, "Couldn't lock mutex: %s", SDL_GetError());
@@ -82,7 +82,7 @@ Run(void *data)
         /* If this sleep isn't done, then threads may starve */
         SDL_Delay(10);
     }
-    if (SDL_ThreadID() == mainthread && doterminate) {
+    if (SDL_ThreadID() == mainthread && SDL_AtomicGet(&doterminate)) {
         SDL_Log("Process %lu:  raising SIGTERM\n", SDL_ThreadID());
         raise(SIGTERM);
     }
@@ -105,6 +105,8 @@ main(int argc, char *argv[])
     }
     atexit(SDL_Quit_Wrapper);
 
+    SDL_AtomicSet(&doterminate, 0);
+
     if ((mutex = SDL_CreateMutex()) == NULL) {
         SDL_LogError(SDL_LOG_CATEGORY_APPLICATION, "Couldn't create mutex: %s\n", SDL_GetError());
         exit(1);

test/testmultiaudio.c

@@ -25,7 +25,7 @@ typedef struct
 {
     SDL_AudioDeviceID dev;
     int soundpos;
-    volatile int done;
+    SDL_atomic_t done;
 } callback_data;
 
 callback_data cbd[64];
@@ -46,14 +46,14 @@ play_through_once(void *arg, Uint8 * stream, int len)
     if (len > 0) {
         stream += cpy;
         SDL_memset(stream, spec.silence, len);
-        cbd->done++;
+        SDL_AtomicSet(&cbd->done, 1);
     }
 }
 
 void
 loop()
 {
-    if(cbd[0].done) {
+    if (SDL_AtomicGet(&cbd[0].done)) {
 #ifdef __EMSCRIPTEN__
         emscripten_cancel_main_loop();
 #endif
@@ -100,8 +100,7 @@ test_multi_audio(int devcount)
 #ifdef __EMSCRIPTEN__
             emscripten_set_main_loop(loop, 0, 1);
 #else
-            while (!cbd[0].done)
-            {
+            while (!SDL_AtomicGet(&cbd[0].done)) {
                 #ifdef __ANDROID__                
                 /* Empty queue, some application events would prevent pause. */
                 while (SDL_PollEvent(&event)){}
@@ -136,7 +135,7 @@ test_multi_audio(int devcount)
     while (keep_going) {
         keep_going = 0;
         for (i = 0; i < devcount; i++) {
-            if ((cbd[i].dev) && (!cbd[i].done)) {
+            if ((cbd[i].dev) && (!SDL_AtomicGet(&cbd[i].done))) {
                 keep_going = 1;
             }
         }

test/torturethread.c

@@ -21,7 +21,7 @@
 
 #define NUMTHREADS 10
 
-static char volatile time_for_threads_to_die[NUMTHREADS];
+static SDL_atomic_t time_for_threads_to_die[NUMTHREADS];
 
 /* Call this instead of exit(), so we can clean up SDL: atexit() is evil. */
 static void
@@ -58,7 +58,7 @@ ThreadFunc(void *data)
     }
 
     SDL_Log("Thread '%d' waiting for signal\n", tid);
-    while (time_for_threads_to_die[tid] != 1) {
+    while (SDL_AtomicGet(&time_for_threads_to_die[tid]) != 1) {
         ;                       /* do nothing */
     }
 
@@ -92,7 +92,7 @@ main(int argc, char *argv[])
     for (i = 0; i < NUMTHREADS; i++) {
         char name[64];
         SDL_snprintf(name, sizeof (name), "Parent%d", i);
-        time_for_threads_to_die[i] = 0;
+        SDL_AtomicSet(&time_for_threads_to_die[i], 0);
         threads[i] = SDL_CreateThread(ThreadFunc, name, (void*) (uintptr_t) i);
 
         if (threads[i] == NULL) {
@@ -102,7 +102,7 @@ main(int argc, char *argv[])
     }
 
     for (i = 0; i < NUMTHREADS; i++) {
-        time_for_threads_to_die[i] = 1;
+        SDL_AtomicSet(&time_for_threads_to_die[i], 1);
     }
 
     for (i = 0; i < NUMTHREADS; i++) {