Index, IndexFunc, Indexers, Indices

[zhouhaibing089]

Source Code: https://github.com/kubernetes/kubernetes/blob/master/staging/src/k8s.io/client-go/tools/cache/index.go.

IndexFunc: takes an object, and produces a list of index values.
Index: a mapping from index value to key set.
Indexers: a mapping from index name to IndexFunc.
Indices: a mapping from index name to Index

// Index returns a list of items that match on the index function
// Index is thread-safe so long as you treat all items as immutable
func (c *threadSafeMap) Index(indexName string, obj interface{}) ([]interface{}, error) {
	c.lock.RLock()
	defer c.lock.RUnlock()

	indexFunc := c.indexers[indexName]
	if indexFunc == nil {
		return nil, fmt.Errorf("Index with name %s does not exist", indexName)
	}

	indexKeys, err := indexFunc(obj)
	if err != nil {
		return nil, err
	}
	index := c.indices[indexName]

	// need to de-dupe the return list.  Since multiple keys are allowed, this can happen.
	returnKeySet := sets.String{}
	for _, indexKey := range indexKeys {
		set := index[indexKey]
		for _, key := range set.UnsortedList() {
			returnKeySet.Insert(key)
		}
	}

	list := make([]interface{}, 0, returnKeySet.Len())
	for absoluteKey := range returnKeySet {
		list = append(list, c.items[absoluteKey])
	}
	return list, nil
}

1. 先通过indexName获取indexFunc.
2. 对obj做indexFunc拿到[]string的index values.
3. 再通过indexName获取index.
4. 对每个index value, 从index中取出key set.
5. 合并所有的key set.
6. 从storage中根据key set取出所有的object.