/
mmap.go
140 lines (111 loc) · 2.86 KB
/
mmap.go
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package m3
import (
"errors"
"os"
"syscall"
mmap "github.com/edsrzf/mmap-go"
)
var ErrUnsafeOperation = errors.New("unsafe operation")
func NewMemMapAppender(file *os.File, blockSize int, offset int64) (Writer, error) {
stat, err := file.Stat()
if err != nil {
return nil, err
}
//
if offset+int64(blockSize) > stat.Size() {
file.Truncate(offset + int64(blockSize))
}
m := &mmapWriter{file, nil, offset, 0, blockSize, true}
err = m.createMap()
if err != nil {
return nil, err
}
return &writer{m}, nil
}
type mmapWriter struct {
file *os.File
m mmap.MMap
fileOffset int64
position int
blockSize int
safe bool
}
func (m *mmapWriter) createMap() error {
m.file.Truncate(m.fileOffset + int64(m.blockSize))
m2, err := mmap.MapRegion(m.file, m.blockSize, syscall.PROT_WRITE|syscall.MAP_PRIVATE, mmap.RDWR, m.fileOffset)
if err != nil {
return err
}
m.m = m2
m.fileOffset += int64(m.blockSize)
return nil
}
func (m *mmapWriter) advance() error {
// unmap mmap
err := m.m.Unmap()
if err != nil {
m.safe = false
return err
}
// create new mmap buffer
err = m.createMap()
if err != nil {
m.safe = false
return err
}
// reset mmap position
m.position = 0
return nil
}
func (m *mmapWriter) remaining() int {
return m.blockSize - m.position
}
func (m *mmapWriter) Write(data []byte) (n int, err error) {
// check mmap safety
if !m.safe {
return 0, ErrUnsafeOperation
}
// check remaining mmap buffer
if m.remaining() == 0 {
err = m.advance()
if err != nil {
m.safe = false
return 0, err
}
}
// iterate until all data has been written
var written int
for written < len(data) {
// if the remaining data fits in the current mmap buffer
if len(data)-written < m.remaining() {
// copy data into mmap buffer
copy(m.m[m.position:], data[written:])
// update mmap position
m.position += len(data)
written = len(data)
} else {
// copy partial data into mmap block
copy(m.m[m.position:], data[written:written+m.remaining()])
written += m.remaining()
// advance mmap buffer
err = m.advance()
if err != nil {
return written, err
}
}
}
return written, nil
}
func (m *mmapWriter) Close() error {
if m.safe {
m.safe = false
// unmap mmap
err := m.m.Unmap()
if err != nil {
return err
}
}
// removes bytes from file which were never written to
m.file.Truncate(m.fileOffset - int64(m.remaining()))
return m.file.Close()
}