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y.go
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y.go
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/*
* Copyright 2017 Dgraph Labs, Inc. and Contributors
*
* 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 y
import (
"bytes"
"encoding/binary"
"hash/crc32"
"math"
"os"
"sync"
"github.com/pkg/errors"
)
// ErrEOF indicates an end of file when trying to read from a memory mapped file
// and encountering the end of slice.
var ErrEOF = errors.New("End of mapped region")
const (
// Sync indicates that O_DSYNC should be set on the underlying file,
// ensuring that data writes do not return until the data is flushed
// to disk.
Sync = 1 << iota
// ReadOnly opens the underlying file on a read-only basis.
ReadOnly
)
var (
// This is O_DSYNC (datasync) on platforms that support it -- see file_unix.go
datasyncFileFlag = 0x0
// CastagnoliCrcTable is a CRC32 polynomial table
CastagnoliCrcTable = crc32.MakeTable(crc32.Castagnoli)
)
// OpenExistingFile opens an existing file, errors if it doesn't exist.
func OpenExistingFile(filename string, flags uint32) (*os.File, error) {
openFlags := os.O_RDWR
if flags&ReadOnly != 0 {
openFlags = os.O_RDONLY
}
if flags&Sync != 0 {
openFlags |= datasyncFileFlag
}
return os.OpenFile(filename, openFlags, 0)
}
// CreateSyncedFile creates a new file (using O_EXCL), errors if it already existed.
func CreateSyncedFile(filename string, sync bool) (*os.File, error) {
flags := os.O_RDWR | os.O_CREATE | os.O_EXCL
if sync {
flags |= datasyncFileFlag
}
return os.OpenFile(filename, flags, 0666)
}
// OpenSyncedFile creates the file if one doesn't exist.
func OpenSyncedFile(filename string, sync bool) (*os.File, error) {
flags := os.O_RDWR | os.O_CREATE
if sync {
flags |= datasyncFileFlag
}
return os.OpenFile(filename, flags, 0666)
}
// OpenTruncFile opens the file with O_RDWR | O_CREATE | O_TRUNC
func OpenTruncFile(filename string, sync bool) (*os.File, error) {
flags := os.O_RDWR | os.O_CREATE | os.O_TRUNC
if sync {
flags |= datasyncFileFlag
}
return os.OpenFile(filename, flags, 0666)
}
// SafeCopy does append(a[:0], src...).
func SafeCopy(a []byte, src []byte) []byte {
return append(a[:0], src...)
}
// Copy copies a byte slice and returns the copied slice.
func Copy(a []byte) []byte {
b := make([]byte, len(a))
copy(b, a)
return b
}
// KeyWithTs generates a new key by appending ts to key.
func KeyWithTs(key []byte, ts uint64) []byte {
out := make([]byte, len(key)+8)
copy(out, key)
binary.BigEndian.PutUint64(out[len(key):], math.MaxUint64-ts)
return out
}
// ParseTs parses the timestamp from the key bytes.
func ParseTs(key []byte) uint64 {
if len(key) <= 8 {
return 0
}
return math.MaxUint64 - binary.BigEndian.Uint64(key[len(key)-8:])
}
// CompareKeys checks the key without timestamp and checks the timestamp if keyNoTs
// is same.
// a<timestamp> would be sorted higher than aa<timestamp> if we use bytes.compare
// All keys should have timestamp.
func CompareKeys(key1 []byte, key2 []byte) int {
AssertTrue(len(key1) > 8 && len(key2) > 8)
if cmp := bytes.Compare(key1[:len(key1)-8], key2[:len(key2)-8]); cmp != 0 {
return cmp
}
return bytes.Compare(key1[len(key1)-8:], key2[len(key2)-8:])
}
// ParseKey parses the actual key from the key bytes.
func ParseKey(key []byte) []byte {
if key == nil {
return nil
}
AssertTruef(len(key) > 8, "key=%q", key)
return key[:len(key)-8]
}
// SameKey checks for key equality ignoring the version timestamp suffix.
func SameKey(src, dst []byte) bool {
if len(src) != len(dst) {
return false
}
return bytes.Equal(ParseKey(src), ParseKey(dst))
}
// Slice holds a reusable buf, will reallocate if you request a larger size than ever before.
// One problem is with n distinct sizes in random order it'll reallocate log(n) times.
type Slice struct {
buf []byte
}
// Resize reuses the Slice's buffer (or makes a new one) and returns a slice in that buffer of
// length sz.
func (s *Slice) Resize(sz int) []byte {
if cap(s.buf) < sz {
s.buf = make([]byte, sz)
}
return s.buf[0:sz]
}
// Closer holds the two things we need to close a goroutine and wait for it to finish: a chan
// to tell the goroutine to shut down, and a WaitGroup with which to wait for it to finish shutting
// down.
type Closer struct {
closed chan struct{}
waiting sync.WaitGroup
}
// NewCloser constructs a new Closer, with an initial count on the WaitGroup.
func NewCloser(initial int) *Closer {
ret := &Closer{closed: make(chan struct{})}
ret.waiting.Add(initial)
return ret
}
// AddRunning Add()'s delta to the WaitGroup.
func (lc *Closer) AddRunning(delta int) {
lc.waiting.Add(delta)
}
// Signal signals the HasBeenClosed signal.
func (lc *Closer) Signal() {
close(lc.closed)
}
// HasBeenClosed gets signaled when Signal() is called.
func (lc *Closer) HasBeenClosed() <-chan struct{} {
return lc.closed
}
// Done calls Done() on the WaitGroup.
func (lc *Closer) Done() {
lc.waiting.Done()
}
// Wait waits on the WaitGroup. (It waits for NewCloser's initial value, AddRunning, and Done
// calls to balance out.)
func (lc *Closer) Wait() {
lc.waiting.Wait()
}
// SignalAndWait calls Signal(), then Wait().
func (lc *Closer) SignalAndWait() {
lc.Signal()
lc.Wait()
}