static uint32_t next_gen_id() {
static uint32_t gNextGenID = 0;
uint32_t genID;
// Loop in case our global wraps around, as we never want to return a 0.
do {
genID = sk_atomic_fetch_add(&gNextGenID, 2u) + 2; // Never set the low bit.
} while (0 == genID);
return genID;
}
uint32_t SkNextID::ImageID() {
static uint32_t gID = 0;
uint32_t id;
// Loop in case our global wraps around, as we never want to return a 0.
do {
id = sk_atomic_fetch_add(&gID, 2u) + 2; // Never set the low bit.
} while (0 == id);
return id;
}
void unref() const {
SkASSERT(fRefCnt > 0);
// A release here acts in place of all releases we "should" have been doing in ref().
if (1 == sk_atomic_fetch_add(&fRefCnt, -1, sk_memory_order_acq_rel)) {
// Like unique(), the acquire is only needed on success.
SkBufferBlock* block = fBlock.fNext;
sk_free((void*)this);
while (block) {
SkBufferBlock* next = block->fNext;
sk_free(block);
block = next;
}
}
}
uint32_t SkPicture::uniqueID() const {
static uint32_t gNextID = 1;
uint32_t id = sk_atomic_load(&fUniqueID, sk_memory_order_relaxed);
while (id == 0) {
uint32_t next = sk_atomic_fetch_add(&gNextID, 1u);
if (sk_atomic_compare_exchange(&fUniqueID, &id, next,
sk_memory_order_relaxed,
sk_memory_order_relaxed)) {
id = next;
} else {
// sk_atomic_compare_exchange replaced id with the current value of fUniqueID.
}
}
return id;
}
void SkBaseSemaphore::signal(int n) {
SkASSERT(n >= 0);
// We only want to call the OS semaphore when our logical count crosses
// from <= 0 to >0 (when we need to wake sleeping threads).
//
// This is easiest to think about with specific examples of prev and n.
// If n == 5 and prev == -3, there are 3 threads sleeping and we signal
// SkTMin(-(-3), 5) == 3 times on the OS semaphore, leaving the count at 2.
//
// If prev >= 0, no threads are waiting, SkTMin(-prev, n) is always <= 0,
// so we don't call the OS semaphore, leaving the count at (prev + n).
int prev = sk_atomic_fetch_add(&fCount, n, sk_memory_order_release);
int toSignal = SkTMin(-prev, n);
if (toSignal > 0) {
this->osSignal(toSignal);
}
}
