code: func (c *Cache) DeleteAll() {
  	var keys []interface{}
  	c.m.Range(func(key interface{}, value interface{}) bool {
  		c.close(key.(string), value.(future))
  		keys = append(keys, key)
  		return true
  	})
  
  	for _, key := range keys {
  		c.m.Delete(key)
  	}
  }
docs: // DeleteAll does the following:
  // - calls Close on all values that implement a Close() function
  // - deletes all entries from the cache