cayley/graph/iterator/materialize_iterator.go

// Copyright 2014 The Cayley Authors. All rights reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package iterator

// A simple iterator that, when first called Contains() or Next() upon, materializes the whole subiterator, stores it locally, and responds. Essentially a cache.

import (
	"fmt"
	"strings"

	"github.com/google/cayley/graph"
)

var abortMaterializeAt = 1000

type result struct {
	id   graph.Value
	tags map[string]graph.Value
}

type Materialize struct {
	uid         uint64
	tags        graph.Tagger
	containsMap map[graph.Value]int
	values      []result
	lastIndex   int
	subIt       graph.Iterator
	hasRun      bool
	aborted     bool
}

func NewMaterialize(sub graph.Iterator) *Materialize {
	return &Materialize{
		uid:         NextUID(),
		containsMap: make(map[graph.Value]int),
		subIt:       sub,
	}
}

func (it *Materialize) UID() uint64 {
	return it.uid
}

func (it *Materialize) Reset() {
	it.subIt.Reset()
	it.lastIndex = 0
}

func (it *Materialize) Close() {
	it.subIt.Close()
	it.containsMap = nil
	it.values = nil
	it.hasRun = false
}

func (it *Materialize) Tagger() *graph.Tagger {
	return &it.tags
}

func (it *Materialize) TagResults(dst map[string]graph.Value) {
	if !it.hasRun {
		return
	}
	for _, tag := range it.tags.Tags() {
		dst[tag] = it.Result()
	}

	for tag, value := range it.values[it.lastIndex].tags {
		dst[tag] = value
	}
}

func (it *Materialize) Clone() graph.Iterator {
	out := NewMaterialize(it.subIt.Clone())
	out.tags.CopyFrom(it)
	return out
}

// Print some information about the iterator.
func (it *Materialize) DebugString(indent int) string {
	return fmt.Sprintf("%s(%s tags: %s Size: %d\n%s)",
		strings.Repeat(" ", indent),
		it.Type(),
		it.tags.Tags(),
		len(it.values),
		it.subIt.DebugString(indent+4),
	)
}

// Register this iterator as a Materialize iterator.
func (it *Materialize) Type() graph.Type { return graph.Materialize }

// DEPRECATED
func (it *Materialize) ResultTree() *graph.ResultTree {
	tree := graph.NewResultTree(it.Result())
	tree.AddSubtree(it.subIt.ResultTree())
	return tree
}

func (it *Materialize) Result() graph.Value {
	if it.lastIndex+1 > len(it.values) {
		return nil
	}
	return it.values[it.lastIndex].id
}

func (it *Materialize) SubIterators() []graph.Iterator {
	return []graph.Iterator{it.subIt}
}

func (it *Materialize) Optimize() (graph.Iterator, bool) {
	newSub, changed := it.subIt.Optimize()
	if changed {
		it.subIt = newSub
		if it.subIt.Type() == graph.Null {
			return it.subIt, true
		}
	}
	return it, false
}

// Size is the number of values stored, if we've got them all.
// Otherwise, guess based on the size of the subiterator.
func (it *Materialize) Size() (int64, bool) {
	if it.hasRun {
		return int64(len(it.values)), true
	}
	return it.subIt.Size()
}

// The entire point of Materialize is to amortize the cost by
// putting it all up front.
func (it *Materialize) Stats() graph.IteratorStats {
	overhead := int64(2)
	size, _ := it.Size()
	subitStats := it.subIt.Stats()
	return graph.IteratorStats{
		ContainsCost: overhead * subitStats.NextCost,
		NextCost:     overhead * subitStats.NextCost,
		Size:         size,
	}
}

func (it *Materialize) Next() (graph.Value, bool) {
	if !it.hasRun {
		it.materializeSet()
	}
	if it.aborted {
		return graph.Next(it.subIt)
	}

	lastVal := it.Result()
	for it.lastIndex < len(it.values) {
		it.lastIndex++
		if it.Result() != lastVal {
			return it.Result(), true
		}
	}
	return nil, false
}

func (it *Materialize) Contains(v graph.Value) bool {
	if !it.hasRun {
		it.materializeSet()
	}
	if it.aborted {
		return it.subIt.Contains(v)
	}
	if i, ok := it.containsMap[v]; ok {
		it.lastIndex = i
		return true
	}
	return false
}

func (it *Materialize) NextResult() bool {
	if !it.hasRun {
		it.materializeSet()
	}
	if it.aborted {
		return it.subIt.NextResult()
	}

	i := it.lastIndex + 1
	if i == len(it.values) {
		return false
	}
	if it.Result() == it.values[i].id {
		it.lastIndex = i
		return true
	}
	return false
}

func (it *Materialize) materializeSet() {
	i := 0
	for {
		val, ok := graph.Next(it.subIt)
		if !ok {
			break
		}
		i += 1
		if i > abortMaterializeAt {
			it.aborted = true
			break
		}
		tags := make(map[string]graph.Value)
		it.subIt.TagResults(tags)
		it.containsMap[val] = len(it.values)
		it.values = append(it.values, result{id: val, tags: tags})
		for it.subIt.NextResult() == true {
			tags := make(map[string]graph.Value)
			it.subIt.TagResults(tags)
			it.values = append(it.values, result{id: val, tags: tags})
		}
	}
	if it.aborted {
		it.values = nil
		it.containsMap = nil
		it.subIt.Reset()
	}
	it.hasRun = true
}