Why creating a Cache requires Double check whether the table exists or not.

[CoolLiuzw]

// Cache returns the existing cache table with given name or creates a new one
// if the table does not exist yet.
func Cache(table string) *CacheTable {
	mutex.RLock()
	t, ok := cache[table]
	mutex.RUnlock()

	if !ok {
		mutex.Lock()
		t, ok = cache[table]
		// Double check whether the table exists or not.
		if !ok {
			t = &CacheTable{
				name:  table,
				items: make(map[interface{}]*CacheItem),
			}
			cache[table] = t
		}
		mutex.Unlock()
	}

	return t
}

[CoolLiuzw]