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/
mmap_buffer_manager.go
87 lines (67 loc) · 1.78 KB
/
mmap_buffer_manager.go
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package datastore
import (
"fmt"
"launchpad.net/gommap"
"os"
"sync"
)
const (
fileMode = 0600
)
var (
pageSize = os.Getpagesize()
)
type UnalignedBuffer struct {
offset int64
length int64
}
func (err UnalignedBuffer) Error() string {
return fmt.Sprintf("Can't acquire buffer for unaligned offset (%d) and length (%d)", err.offset, err.length)
}
type SectionAccrossPages struct {
offset int64
length int64
}
func (err SectionAccrossPages) Error() string {
return fmt.Sprintf("Section is spread accross different pages! offset: %d; length: %d", err.offset, err.length)
}
type mMapBufferManager struct {
fd *os.File
mtx map[int]sync.Mutex
}
func NewMMapBufferManager(path string) BufferManager {
fd, err := os.OpenFile(path, os.O_RDWR|os.O_APPEND|os.O_CREATE, fileMode)
if err != nil {
panic(err)
}
return &mMapBufferManager{fd: fd}
}
func (mngr *mMapBufferManager) Acquire(offset, length int64) ([]byte, error) {
if int64(pageSize)%length != 0 || offset%length != 0 {
return nil, UnalignedBuffer{offset, length}
}
page, err := pageForSection(offset, length)
if err != nil {
return nil, err
}
relOffset := offset % int64(pageSize)
mmap, err := gommap.MapAt(0, mngr.fd.Fd(), int64(page)*int64(pageSize), int64(pageSize), gommap.PROT_READ|gommap.PROT_WRITE, gommap.MAP_SHARED)
return []byte(mmap)[relOffset : relOffset+length], err
}
func (mngr *mMapBufferManager) Release(buf []byte) error {
mmap := gommap.MMap(buf)
err := mmap.Sync(gommap.MS_SYNC)
if err != nil {
return err
}
err = mmap.Unlock()
return err
}
func pageForSection(offset, length int64) (int, error) {
offsetPage := offset / int64(pageSize)
lengthPage := length / int64(pageSize)
if offsetPage != lengthPage {
return 0, SectionAccrossPages{offset, length}
}
return int(offsetPage), nil
}