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Added a test to measure the impact of a separate thread periodically …
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…locking the queue entirely.
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@slouken
slouken committed Jan 26, 2011
1 parent e4ed129 commit b4c5c89
Showing 1 changed file with 99 additions and 26 deletions.
125 changes: 99 additions & 26 deletions test/testatomic.c
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Expand Up @@ -234,6 +234,11 @@ void RunEpicTest()
/**************************************************************************/
/* Lock-free FIFO test */

/* This is useful to test the impact of another thread locking the queue
entirely for heavy-weight manipulation.
*/
#define TEST_SPINLOCK_FIFO

#define NUM_READERS 4
#define NUM_WRITERS 4
#define EVENTS_PER_WRITER 1000000
Expand Down Expand Up @@ -265,6 +270,14 @@ typedef struct

char cache_pad3[CACHELINE-sizeof(SDL_atomic_t)];

#ifdef TEST_SPINLOCK_FIFO
SDL_SpinLock lock;
SDL_atomic_t rwcount;
SDL_atomic_t watcher;

char cache_pad4[CACHELINE-sizeof(SDL_SpinLock)-2*sizeof(SDL_atomic_t)];
#endif

SDL_bool active;

/* Only needed for the mutex test */
Expand All @@ -281,6 +294,10 @@ static void InitEventQueue(SDL_EventQueue *queue)
}
SDL_AtomicSet(&queue->enqueue_pos, 0);
SDL_AtomicSet(&queue->dequeue_pos, 0);
#ifdef TEST_SPINLOCK_FIFO
queue->lock = 0;
SDL_AtomicSet(&queue->rwcount, 0);
#endif
queue->active = SDL_TRUE;
}

Expand All @@ -290,6 +307,15 @@ static SDL_bool EnqueueEvent_LockFree(SDL_EventQueue *queue, const SDL_Event *ev
unsigned queue_pos;
unsigned entry_seq;
int delta;
SDL_bool status;

#ifdef TEST_SPINLOCK_FIFO
/* This is a gate so an external thread can lock the queue */
SDL_AtomicLock(&queue->lock);
SDL_assert(SDL_AtomicGet(&queue->watcher) == 0);
SDL_AtomicIncRef(&queue->rwcount);
SDL_AtomicUnlock(&queue->lock);
#endif

queue_pos = (unsigned)SDL_AtomicGet(&queue->enqueue_pos);
for ( ; ; ) {
Expand All @@ -300,22 +326,26 @@ static SDL_bool EnqueueEvent_LockFree(SDL_EventQueue *queue, const SDL_Event *ev
if (delta == 0) {
/* The entry and the queue position match, try to increment the queue position */
if (SDL_AtomicCAS(&queue->enqueue_pos, (int)queue_pos, (int)(queue_pos+1))) {
/* We own the object, fill it! */
entry->event = *event;
SDL_AtomicSet(&entry->sequence, (int)(queue_pos + 1));
status = SDL_TRUE;
break;
}
} else if (delta < 0) {
/* We ran into an old queue entry, which means it still needs to be dequeued */
return SDL_FALSE;
status = SDL_FALSE;
break;
} else {
/* We ran into a new queue entry, get the new queue position */
queue_pos = (unsigned)SDL_AtomicGet(&queue->enqueue_pos);
}
}

/* We own the object, fill it! */
entry->event = *event;
SDL_AtomicSet(&entry->sequence, (int)(queue_pos + 1));

return SDL_TRUE;
#ifdef TEST_SPINLOCK_FIFO
SDL_AtomicDecRef(&queue->rwcount);
#endif
return status;
}

static SDL_bool DequeueEvent_LockFree(SDL_EventQueue *queue, SDL_Event *event)
Expand All @@ -324,6 +354,15 @@ static SDL_bool DequeueEvent_LockFree(SDL_EventQueue *queue, SDL_Event *event)
unsigned queue_pos;
unsigned entry_seq;
int delta;
SDL_bool status;

#ifdef TEST_SPINLOCK_FIFO
/* This is a gate so an external thread can lock the queue */
SDL_AtomicLock(&queue->lock);
SDL_assert(SDL_AtomicGet(&queue->watcher) == 0);
SDL_AtomicIncRef(&queue->rwcount);
SDL_AtomicUnlock(&queue->lock);
#endif

queue_pos = (unsigned)SDL_AtomicGet(&queue->dequeue_pos);
for ( ; ; ) {
Expand All @@ -334,22 +373,26 @@ static SDL_bool DequeueEvent_LockFree(SDL_EventQueue *queue, SDL_Event *event)
if (delta == 0) {
/* The entry and the queue position match, try to increment the queue position */
if (SDL_AtomicCAS(&queue->dequeue_pos, (int)queue_pos, (int)(queue_pos+1))) {
/* We own the object, fill it! */
*event = entry->event;
SDL_AtomicSet(&entry->sequence, (int)(queue_pos+MAX_ENTRIES));
status = SDL_TRUE;
break;
}
} else if (delta < 0) {
/* We ran into an old queue entry, which means we've hit empty */
return SDL_FALSE;
status = SDL_FALSE;
break;
} else {
/* We ran into a new queue entry, get the new queue position */
queue_pos = (unsigned)SDL_AtomicGet(&queue->dequeue_pos);
}
}

/* We own the object, fill it! */
*event = entry->event;
SDL_AtomicSet(&entry->sequence, (int)(queue_pos+MAX_ENTRIES));

return SDL_TRUE;
#ifdef TEST_SPINLOCK_FIFO
SDL_AtomicDecRef(&queue->rwcount);
#endif
return status;
}

static SDL_bool EnqueueEvent_Mutex(SDL_EventQueue *queue, const SDL_Event *event)
Expand All @@ -358,6 +401,7 @@ static SDL_bool EnqueueEvent_Mutex(SDL_EventQueue *queue, const SDL_Event *event
unsigned queue_pos;
unsigned entry_seq;
int delta;
SDL_bool status = SDL_FALSE;

SDL_mutexP(queue->mutex);

Expand All @@ -368,21 +412,20 @@ static SDL_bool EnqueueEvent_Mutex(SDL_EventQueue *queue, const SDL_Event *event
delta = (int)(entry_seq - queue_pos);
if (delta == 0) {
++queue->enqueue_pos.value;

/* We own the object, fill it! */
entry->event = *event;
entry->sequence.value = (int)(queue_pos + 1);
status = SDL_TRUE;
} else if (delta < 0) {
/* We ran into an old queue entry, which means it still needs to be dequeued */
SDL_mutexV(queue->mutex);
return SDL_FALSE;
} else {
printf("ERROR: mutex failed!\n");
}

/* We own the object, fill it! */
entry->event = *event;
entry->sequence.value = (int)(queue_pos + 1);

SDL_mutexV(queue->mutex);

return SDL_TRUE;
return status;
}

static SDL_bool DequeueEvent_Mutex(SDL_EventQueue *queue, SDL_Event *event)
Expand All @@ -391,6 +434,7 @@ static SDL_bool DequeueEvent_Mutex(SDL_EventQueue *queue, SDL_Event *event)
unsigned queue_pos;
unsigned entry_seq;
int delta;
SDL_bool status = SDL_FALSE;

SDL_mutexP(queue->mutex);

Expand All @@ -401,21 +445,20 @@ static SDL_bool DequeueEvent_Mutex(SDL_EventQueue *queue, SDL_Event *event)
delta = (int)(entry_seq - (queue_pos + 1));
if (delta == 0) {
++queue->dequeue_pos.value;

/* We own the object, fill it! */
*event = entry->event;
entry->sequence.value = (int)(queue_pos + MAX_ENTRIES);
status = SDL_TRUE;
} else if (delta < 0) {
/* We ran into an old queue entry, which means we've hit empty */
SDL_mutexV(queue->mutex);
return SDL_FALSE;
} else {
printf("ERROR: mutex failed!\n");
}

/* We own the object, fill it! */
*event = entry->event;
entry->sequence.value = (int)(queue_pos + MAX_ENTRIES);

SDL_mutexV(queue->mutex);

return SDL_TRUE;
return status;
}

static SDL_sem *writersDone;
Expand Down Expand Up @@ -517,6 +560,29 @@ static int FIFO_Reader(void* _data)
return 0;
}

#ifdef TEST_SPINLOCK_FIFO
/* This thread periodically locks the queue for no particular reason */
static int FIFO_Watcher(void* _data)
{
SDL_EventQueue *queue = (SDL_EventQueue *)_data;

while (queue->active) {
SDL_AtomicLock(&queue->lock);
SDL_AtomicIncRef(&queue->watcher);
while (SDL_AtomicGet(&queue->rwcount) > 0) {
SDL_Delay(0);
}
/* Do queue manipulation here... */
SDL_AtomicDecRef(&queue->watcher);
SDL_AtomicUnlock(&queue->lock);

/* Wait a bit... */
SDL_Delay(1);
}
return 0;
}
#endif /* TEST_SPINLOCK_FIFO */

static void RunFIFOTest(SDL_bool lock_free)
{
SDL_EventQueue queue;
Expand All @@ -541,6 +607,13 @@ static void RunFIFOTest(SDL_bool lock_free)

start = SDL_GetTicks();

#ifdef TEST_SPINLOCK_FIFO
/* Start a monitoring thread */
if (lock_free) {
SDL_CreateThread(FIFO_Watcher, &queue);
}
#endif

/* Start the readers first */
printf("Starting %d readers\n", NUM_READERS);
SDL_zero(readerData);
Expand Down

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