1 // Copyright 2015 The etcd Authors 2 // 3 // Licensed under the Apache License, Version 2.0 (the "License"); 4 // you may not use this file except in compliance with the License. 5 // You may obtain a copy of the License at 6 // 7 // http://www.apache.org/licenses/LICENSE-2.0 8 // 9 // Unless required by applicable law or agreed to in writing, software 10 // distributed under the License is distributed on an "AS IS" BASIS, 11 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 12 // See the License for the specific language governing permissions and 13 // limitations under the License. 14 15 package mvcc 16 17 import "encoding/binary" 18 19 // revBytesLen is the byte length of a normal revision. 20 // First 8 bytes is the revision.main in big-endian format. The 9th byte 21 // is a '_'. The last 8 bytes is the revision.sub in big-endian format. 22 const revBytesLen = 8 + 1 + 8 23 24 // A revision indicates modification of the key-value space. 25 // The set of changes that share same main revision changes the key-value space atomically. 26 type revision struct { 27 // main is the main revision of a set of changes that happen atomically. 28 main int64 29 30 // sub is the sub revision of a change in a set of changes that happen 31 // atomically. Each change has different increasing sub revision in that 32 // set. 33 sub int64 34 } 35 36 func (a revision) GreaterThan(b revision) bool { 37 if a.main > b.main { 38 return true 39 } 40 if a.main < b.main { 41 return false 42 } 43 return a.sub > b.sub 44 } 45 46 func newRevBytes() []byte { 47 return make([]byte, revBytesLen, markedRevBytesLen) 48 } 49 50 func revToBytes(rev revision, bytes []byte) { 51 binary.BigEndian.PutUint64(bytes, uint64(rev.main)) 52 bytes[8] = '_' 53 binary.BigEndian.PutUint64(bytes[9:], uint64(rev.sub)) 54 } 55 56 func bytesToRev(bytes []byte) revision { 57 return revision{ 58 main: int64(binary.BigEndian.Uint64(bytes[0:8])), 59 sub: int64(binary.BigEndian.Uint64(bytes[9:])), 60 } 61 } 62 63 type revisions []revision 64 65 func (a revisions) Len() int { return len(a) } 66 func (a revisions) Less(i, j int) bool { return a[j].GreaterThan(a[i]) } 67 func (a revisions) Swap(i, j int) { a[i], a[j] = a[j], a[i] } 68