Most people probably regard metastability as a solved issue, or rather an issue that barely surfaces. Common wisdom tells us that if you fear that metastability is an issue, then all you need to do is add a synchronizer or wait long enough until it goes away. But when is a synchronizer necessary? And how long is long enough? Measuring metastability is difficult at best in real circuits, more often than not it is impossible to measure directly. Simulation is an alternative, but it is not without problems.
