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listvalueiterator.go
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/
listvalueiterator.go
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// Copyright 2019 Nick Poorman
//
// 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
import (
"fmt"
"sync/atomic"
"github.com/apache/arrow/go/v10/arrow"
"github.com/apache/arrow/go/v10/arrow/array"
"github.com/gomem/gomem/internal/debug"
)
// ListValueIterator iterates over the list elements.
// For example, in a list like: [[0 1 2] (null) [3 4 5] [6 7 8] (null)]
// First [0 1 2] would be returned, then (null), then [3 4 5], etc..
type ListValueIterator struct {
refCount int64
chunkIterator *ChunkIterator
// Things we need to maintain for the iterator
index int // current value index
ref *array.List // the chunk reference
done bool // there are no more elements for this iterator
dataType arrow.DataType
elemDataType arrow.DataType
}
func NewListValueIterator(col *arrow.Column) *ListValueIterator {
// We need a ChunkIterator to read the chunks
chunkIterator := NewChunkIterator(col)
elemDataType := col.DataType().(*arrow.ListType).Elem()
return &ListValueIterator{
refCount: 1,
chunkIterator: chunkIterator,
index: 0,
ref: nil,
dataType: col.DataType(),
elemDataType: elemDataType,
}
}
func (vr *ListValueIterator) ValueInterface() interface{} {
fmt.Println("called ListValueIterator ValueInterface")
if vr.ref.IsNull(vr.index) {
return nil
}
j := vr.index + vr.ref.Offset() // index + data offset
offsets := vr.ref.Offsets()
beg := int64(offsets[j])
end := int64(offsets[j+1])
arr := array.NewSlice(vr.ref.ListValues(), beg, end)
defer arr.Release()
return NewInterfaceValueIterator(
arrow.Field{Name: "item", Type: vr.elemDataType, Nullable: true},
arr,
)
}
// ValueAsJSON returns the current value as an interface{} in it's JSON representation.
func (vr *ListValueIterator) ValueAsJSON() (interface{}, error) {
if vr.ref.IsNull(vr.index) {
return nil, nil
}
j := vr.index + vr.ref.Offset() // index + data offset
offsets := vr.ref.Offsets()
beg := offsets[j]
end := offsets[j+1]
arr := array.NewSlice(vr.ref.ListValues(), int64(beg), int64(end))
defer arr.Release()
iter := NewInterfaceValueIterator(
arrow.Field{Name: "item", Type: vr.elemDataType, Nullable: true},
arr,
)
defer iter.Release()
list := make([]interface{}, 0, end-beg)
for iter.Next() {
jsonValue, err := iter.ValueAsJSON()
if err != nil {
return nil, err
}
list = append(list, jsonValue)
}
return list, nil
}
func (vr *ListValueIterator) DataType() arrow.DataType {
return vr.dataType
}
func (vr *ListValueIterator) Next() bool {
if vr.done {
return false
}
// Move the index up
vr.index++
// Keep moving the chunk up until we get one with data
for vr.ref == nil || vr.index >= vr.ref.Len() {
if !vr.nextChunk() {
// There were no more chunks with data in them
vr.done = true
return false
}
}
return true
}
func (vr *ListValueIterator) nextChunk() bool {
// Advance the chunk until we get one with data in it or we are done
if !vr.chunkIterator.Next() {
// No more chunks
return false
}
// There was another chunk.
// We maintain the ref and the values because the ref is going to allow us to retain the memory.
ref := vr.chunkIterator.Chunk()
ref.Retain()
if vr.ref != nil {
vr.ref.Release()
}
vr.ref = ref.(*array.List)
vr.index = 0
return true
}
// Retain keeps a reference to the ListValueIterator
func (vr *ListValueIterator) Retain() {
atomic.AddInt64(&vr.refCount, 1)
}
// Release removes a reference to the ListValueIterator
func (vr *ListValueIterator) Release() {
debug.Assert(atomic.LoadInt64(&vr.refCount) > 0, "too many releases")
if atomic.AddInt64(&vr.refCount, -1) == 0 {
if vr.chunkIterator != nil {
vr.chunkIterator.Release()
vr.chunkIterator = nil
}
if vr.ref != nil {
vr.ref.Release()
vr.ref = nil
}
}
}