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combined_iterator.go
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/
combined_iterator.go
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package graveler
import (
"bytes"
)
// CombinedIterator iterates over two listing iterators,
// in case of duplication (in values or in errors) returns value in iterA.
// CombinedIterator can be constructed from other CombinedIterator to allow
// chaining of multiple ValueIterators.
type CombinedIterator struct {
iterA ValueIterator
iterB ValueIterator
p ValueIterator
}
// NewCombinedIterator combines multiple ValueIterators into a single CombinedIterator.
// The returned iterator precedence order is first-to-last in case of matching keys in 2 or more iterators.
func NewCombinedIterator(iters ...ValueIterator) ValueIterator {
if len(iters) == 0 {
panic("at least one iterator is required")
}
if len(iters) == 1 {
return iters[0]
}
iter := newCombinedIterator(iters[0], iters[1])
for i := 2; i < len(iters); i++ {
iter = newCombinedIterator(iter, iters[i])
}
return iter
}
func newCombinedIterator(iterA, iterB ValueIterator) *CombinedIterator {
return &CombinedIterator{
iterA: iterA,
iterB: iterB,
p: nil,
}
}
// advanceInnerIterators advances the inner iterators and returns true if it has more
func (c *CombinedIterator) advanceInnerIterators() bool {
valA := c.iterA.Value()
valB := c.iterB.Value()
var nextA bool
var nextB bool
switch {
case c.p == nil:
// first
nextA = c.iterA.Next()
nextB = c.iterB.Next()
case valA == nil && valB == nil:
// last
return false
case valA == nil:
// iterA is done
c.p = c.iterB
nextB = c.iterB.Next()
case valB == nil:
// iterB is done
c.p = c.iterA
nextA = c.iterA.Next()
case bytes.Equal(valA.Key, valB.Key):
nextA = c.iterA.Next()
nextB = c.iterB.Next()
case bytes.Compare(valA.Key, valB.Key) < 0:
nextA = c.iterA.Next()
nextB = true
default:
// value of iterA < value of iterB
nextB = c.iterB.Next()
nextA = true
}
if c.iterA.Err() != nil {
c.p = c.iterA
return false
}
if c.iterB.Err() != nil {
c.p = c.iterB
return false
}
return nextA || nextB
}
func (c *CombinedIterator) Next() bool {
if !c.advanceInnerIterators() {
return false
}
// set c.p to be the next (smaller) value
valA := c.iterA.Value()
valB := c.iterB.Value()
switch {
case valA == nil && valB == nil:
c.p = c.iterA
return false
case valA == nil:
c.p = c.iterB
case valB == nil:
c.p = c.iterA
case bytes.Compare(valA.Key, valB.Key) <= 0:
c.p = c.iterA
default:
c.p = c.iterB
}
return true
}
func (c *CombinedIterator) SeekGE(id Key) {
c.p = nil
c.iterA.SeekGE(id)
c.iterB.SeekGE(id)
}
func (c *CombinedIterator) Value() *ValueRecord {
if c.p == nil {
return nil
}
return c.p.Value()
}
func (c *CombinedIterator) Err() error {
if c.p == nil {
return nil
}
return c.p.Err()
}
func (c *CombinedIterator) Close() {
c.iterA.Close()
c.iterB.Close()
}
// FilterTombstoneIterator wraps a value iterator and filters out tombstones.
type FilterTombstoneIterator struct {
iter ValueIterator
}
func NewFilterTombstoneIterator(iter ValueIterator) *FilterTombstoneIterator {
return &FilterTombstoneIterator{iter: iter}
}
func (f *FilterTombstoneIterator) Next() bool {
for f.iter.Next() {
if !f.iter.Value().IsTombstone() {
return true
}
}
return false
}
func (f *FilterTombstoneIterator) SeekGE(id Key) {
f.iter.SeekGE(id)
}
func (f *FilterTombstoneIterator) Value() *ValueRecord {
return f.iter.Value()
}
func (f *FilterTombstoneIterator) Err() error {
return f.iter.Err()
}
func (f *FilterTombstoneIterator) Close() {
f.iter.Close()
}