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memmap.go
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memmap.go
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// Copyright 2016 Stanislav Liberman
//
// 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 memmap
import (
"errors"
"fmt"
"log"
"os"
"sync"
"syscall"
"unsafe"
mapper "github.com/edsrzf/mmap-go"
"github.com/op/go-logging"
)
// File is the wrapper around memory mapped file
type File struct {
mmap unsafe.Pointer
size int
}
var logger = logging.MustGetLogger("memmap")
// We keep this map so that we can get back the original handle from the memory address.
// map[unsafe.Pointer]mapper.MMap
var memories = sync.Map{}
// GetFileSize is a helper function to retrieve file size
func GetFileSize(filename string) int64 {
file, err := os.Open(filename)
if err != nil {
logger.Error(err)
return -1
}
defer file.Close()
fi, err := file.Stat()
if err != nil {
logger.Fatal(err)
return -1
}
return fi.Size()
}
// MapExisting is the factory method used to create memory maps for existing file. This function will fail if
// the file does not exist.
func MapExisting(filename string, offset int64, length int) (*File, error) {
logger.Debugf("Will try to map existing %s, %d, %d", filename, offset, length)
f, err := os.OpenFile(filename, syscall.O_RDWR, 0644)
if err != nil {
return nil, err
}
defer f.Close()
fi, err := f.Stat()
if err != nil {
return nil, err
}
size := fi.Size()
if size == 0 {
return nil, errors.New("zero size for existing file")
}
if size < 0 {
return nil, fmt.Errorf("mmap: stat %q returned %d", filename, size)
}
if size != int64(size) {
return nil, fmt.Errorf("mmap: file %q is too large", filename)
}
var mapSize int
if length != 0 {
mapSize = length
} else {
mapSize = int(size)
}
logger.Debugf("Mapping existing file: fd: %d, size: %d, offset: %d", f.Fd(), size, offset)
mmap, err := doMap(f, offset, mapSize)
logger.Debugf("Mapped existing file @%v for %d", mmap.mmap, mmap.size)
return mmap, err
}
// NewFile is a factory method to create a new memory mapped file with the specified capacity
func NewFile(filename string, offset int64, length int) (*File, error) {
logger.Debugf("Will try to map new %s, %d, %d", filename, offset, length)
f, err := os.Create(filename)
if err != nil {
return nil, err
}
defer f.Close()
_, err = f.Seek(int64(length-1), 0)
if err != nil {
log.Fatal(err)
}
_, err = f.Write([]byte("\000"))
if err != nil {
log.Fatal(err)
}
mmap, err := doMap(f, offset, length)
logger.Debugf("Mapped a new file @%v for %d", mmap.mmap, mmap.size)
return mmap, err
}
// GetMemoryPtr return the pointer to the mapped region of the file
func (mmap *File) GetMemoryPtr() unsafe.Pointer {
return mmap.mmap
}
// GetMemorySize return the size of the mapped region of the file
func (mmap *File) GetMemorySize() int {
return mmap.size
}
// Close attempts to unmap the mapped memory region
func (mmap *File) Close() (err error) {
mm, _ := memories.Load(mmap.mmap)
tomap := mm.(mapper.MMap)
return tomap.Unmap()
}
func doMap(f *os.File, offset int64, length int) (*File, error) {
mm, err := mapper.MapRegion(f, length, mapper.RDWR, 0, offset)
if err != nil {
return nil, err
}
mmap := new(File)
mmap.mmap = unsafe.Pointer(&mm[0])
mmap.size = length
memories.Store(mmap.mmap, mm)
return mmap, err
}