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segment.go
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segment.go
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// Copyright (c) 2016 Uber Technologies, Inc.
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.
package ts
import (
"bytes"
"github.com/m3db/m3/src/x/checked"
"github.com/m3db/m3/src/x/pool"
"github.com/m3db/stackadler32"
)
// Segment represents a binary blob consisting of two byte slices and
// declares whether they should be finalized when the segment is finalized.
type Segment struct {
// Head is the head of the segment.
Head checked.Bytes
// Tail is the tail of the segment.
Tail checked.Bytes
// SegmentFlags declares whether to finalize when finalizing the segment.
Flags SegmentFlags
// checksum is the checksum for the segment.
checksum uint32
}
// SegmentFlags describes the option to finalize or not finalize
// bytes in a Segment.
type SegmentFlags uint8
const (
// FinalizeNone specifies to finalize neither of the bytes
FinalizeNone SegmentFlags = 1 << 0
// FinalizeHead specifies to finalize the head bytes
FinalizeHead SegmentFlags = 1 << 1
// FinalizeTail specifies to finalize the tail bytes
FinalizeTail SegmentFlags = 1 << 2
)
// CalculateChecksum calculates and sets the 32-bit checksum for
// this segment avoiding any allocations.
func (s *Segment) CalculateChecksum() uint32 {
if s.checksum != 0 {
return s.checksum
}
d := stackadler32.NewDigest()
if s.Head != nil {
d = d.Update(s.Head.Bytes())
}
if s.Tail != nil {
d = d.Update(s.Tail.Bytes())
}
s.checksum = d.Sum32()
return s.checksum
}
// NewSegment will create a new segment and increment the refs to
// head and tail if they are non-nil. When finalized the segment will
// also finalize the byte slices if FinalizeBytes is passed.
func NewSegment(
head, tail checked.Bytes,
checksum uint32,
flags SegmentFlags,
) Segment {
if head != nil {
head.IncRef()
}
if tail != nil {
tail.IncRef()
}
return Segment{
Head: head,
Tail: tail,
Flags: flags,
checksum: checksum,
}
}
// Len returns the length of the head and tail.
func (s *Segment) Len() int {
var total int
if s.Head != nil {
total += s.Head.Len()
}
if s.Tail != nil {
total += s.Tail.Len()
}
return total
}
// Equal returns if this segment is equal to another.
// WARNING: This should only be used in code paths not
// executed often as it allocates bytes to concat each
// segment head and tail together before comparing the contents.
func (s *Segment) Equal(other *Segment) bool {
var head, tail, otherHead, otherTail []byte
if s.Head != nil {
head = s.Head.Bytes()
}
if s.Tail != nil {
tail = s.Tail.Bytes()
}
if other.Head != nil {
otherHead = other.Head.Bytes()
}
if other.Tail != nil {
otherTail = other.Tail.Bytes()
}
return bytes.Equal(append(head, tail...), append(otherHead, otherTail...))
}
// Finalize will finalize the segment by decrementing refs to head and
// tail if they are non-nil.
func (s *Segment) Finalize() {
if s.Head != nil {
s.Head.DecRef()
if s.Flags&FinalizeHead == FinalizeHead {
s.Head.Finalize()
}
}
s.Head = nil
if s.Tail != nil {
s.Tail.DecRef()
if s.Flags&FinalizeTail == FinalizeTail {
s.Tail.Finalize()
}
}
s.Tail = nil
}
// Clone will create a copy of this segment with an optional bytes pool.
func (s *Segment) Clone(pool pool.CheckedBytesPool) Segment {
var (
checkedHead, checkedTail checked.Bytes
tail []byte
)
head := s.Head.Bytes()
if s.Tail != nil {
tail = s.Tail.Bytes()
}
if pool != nil {
checkedHead = pool.Get(len(head))
checkedHead.IncRef()
checkedHead.AppendAll(head)
checkedHead.DecRef()
if tail != nil {
checkedTail = pool.Get(len(tail))
checkedTail.IncRef()
checkedTail.AppendAll(tail)
checkedTail.DecRef()
}
} else {
ch := make([]byte, len(head))
copy(ch, head)
checkedHead = checked.NewBytes(ch, nil)
if tail != nil {
ct := make([]byte, len(tail))
copy(ct, tail)
checkedTail = checked.NewBytes(ct, nil)
}
}
// NB: new segment is always finalizeable.
return NewSegment(checkedHead, checkedTail,
s.CalculateChecksum(), FinalizeHead&FinalizeTail)
}