registry.go
func (r *Registry) Size() int {
	r.mutex.RLock()
	size := len(r.instruments)
	r.mutex.RUnlock()
	return size
}
func (r *Registry) Size() int {
	r.mutex.RLock()
	size := len(r.instruments)
	r.mutex.RUnlock()
	return size
}
func ( r * Registry ) Size ( ) int { r . mutex . RLock ( ) size := len ( r . instruments ) r . mutex . RUnlock ( ) return size }
// Size returns the numbers of instruments in the registry.
Size returns the numbers of instruments in the registry .