private void AcquireLock(InstanceScopedStripedLockProvider provider, string key)
{
// Monitor.Enter and Monitor.Exit are tied to a specific thread and are
// slower than this spin lock, which does not care about threads and will execute very
// quickly, regardless of lock contention
// https://stackoverflow.com/questions/11001760/monitor-enter-and-monitor-exit-in-different-threads
// make unchecked just in case compiler is doing extra checks in the int to uint cast
unchecked
{
// Get a hash based on the key, use this to lock on a specific int in the array. The array is designed
// to be small enough to not use very much memory, but large enough to avoid collisions.
// Even if there is a collision, it will be resolved very quickly.
_hash = (uint)(key ?? string.Empty).GetHashCode() % (uint)provider.keyLocks.Length;
}
// To get the lock, we must change the int at hash index from a 0 to a 1. If the value is
// already a 1, we don't get the lock. The return value must be 0 (the original value of the int).
// it is very unlikely to have any contention here, but if so, the spin cycle should be very short.
// Parameter index 1 (value of 1) is the value to change to if the existing value (Parameter index 2) is 0.
while (Interlocked.CompareExchange(ref provider.keyLocks[_hash], 1, 0) == 1)
{
// give up a clock cycle, we want to get back and try to get the lock again very quickly
System.Threading.Thread.Yield();
}
_lockProvider = provider;
}
public InstanceScopedStripedLockReleaser(InstanceScopedStripedLockProvider provider, string key)
{
AcquireLock(provider, key);
}