Locking multiple parts of an array - Multithreading - c++

Question

I'm trying to implement a threadsafe locking mechanism for an array with the following intended use case:
Request the indexes you want to lock and try to acquire them. If you fail to acquire ANY index, bail out, and try again (essentially spin).
Once the necessary locks have been acquired perform processing on these indexes.
Release the acquired locks!
I'm using the below code to test the lock - it just increments a test count, with the same indexes being specified for each iteration (so it forces access to be sequential). The only problem is it doesn't work, and I'm kind of stumped...
I have a feeling I'm missing some sort of key race condition, but I can't identity it yet :(
#pragma omp parallel for
for (int i = 0; i < activeItems; i++)
{
std::vector<int> lockedBucketIndexes = {0, 1, 2, 3};
//try and get a lock on the buckets we want, otherwise keep trying
while (!spatialHash->TryAcquireBucketLocks(lockedBucketIndexes))
{
//TODO - do some fancy backoff here
}
testCount++;
spatialHash->DropBucketLocks(lockedBucketIndexes);
}
The class/methods that do the locking:
std::vector<int> _bucketLocks;
SpinLock _bucketLockLock;
bool SpatialHash::TryAcquireBucketLocks(std::vector<int> bucketIndexes)
{
bool success = true;
//try and get a lock to set our bucket locks... lockception
_bucketLockLock.lock();
//quickly check that the buckets we want are free
for each (int bucketIndex in bucketIndexes)
{
if (_bucketLocks[bucketIndex] > 0)
{
success = false;
break;
}
}
//if all the buckets are free, set them to occupied
if (success)
{
for each (int bucketIndex in bucketIndexes)
{
_bucketLocks[bucketIndex] = 1;
}
}
//let go of the lock
_bucketLockLock.unlock();
return success;
}
void DropBucketLocks(std::vector<int> bucketIndexes)
{
//I have no idea why these locks are required
//It seems to almost work with them though...
_bucketLockLock.lock();
for each (int bucketIndex in bucketIndexes)
{
_bucketLocks[bucketIndex] = 0;
}
_bucketLockLock.unlock();
return true;
}
The spinlock class:
class SpinLock {
std::atomic_flag locked = ATOMIC_FLAG_INIT;
public:
void lock() {
while (locked.test_and_set(std::memory_order_acquire)) { ; }
}
void unlock() {
locked.clear(std::memory_order_release);
}
};