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Fix ReadAt + WriteAt concurrency #448

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Fix ReadAt + WriteAt concurrency #448

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41 changes: 18 additions & 23 deletions mem/file.go
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Original file line number Diff line number Diff line change
Expand Up @@ -201,33 +201,30 @@ func (f *File) ReadDir(n int) ([]fs.DirEntry, error) {
return di, nil
}

func (f *File) Read(b []byte) (n int, err error) {
func (f *File) ReadAt(b []byte, off int64) (n int, err error) {
f.fileData.Lock()
defer f.fileData.Unlock()
if f.closed {
return 0, ErrFileClosed
}
if len(b) > 0 && int(f.at) == len(f.fileData.data) {
if len(b) > 0 && int(off) == len(f.fileData.data) {
return 0, io.EOF
}
if int(f.at) > len(f.fileData.data) {
if int(off) > len(f.fileData.data) {
return 0, io.ErrUnexpectedEOF
}
if len(f.fileData.data)-int(f.at) >= len(b) {
if len(f.fileData.data)-int(off) >= len(b) {
n = len(b)
} else {
n = len(f.fileData.data) - int(f.at)
n = len(f.fileData.data) - int(off)
}
copy(b, f.fileData.data[f.at:f.at+int64(n)])
atomic.AddInt64(&f.at, int64(n))
copy(b, f.fileData.data[off:off+int64(n)])
return
}

func (f *File) ReadAt(b []byte, off int64) (n int, err error) {
prev := atomic.LoadInt64(&f.at)
atomic.StoreInt64(&f.at, off)
n, err = f.Read(b)
atomic.StoreInt64(&f.at, prev)
func (f *File) Read(b []byte) (n int, err error) {
n, err = f.ReadAt(b, atomic.LoadInt64(&f.at))
atomic.AddInt64(&f.at, int64(n))
return
}

Expand Down Expand Up @@ -268,38 +265,36 @@ func (f *File) Seek(offset int64, whence int) (int64, error) {
return f.at, nil
}

func (f *File) Write(b []byte) (n int, err error) {
func (f *File) WriteAt(b []byte, off int64) (n int, err error) {
if f.closed {
return 0, ErrFileClosed
}
if f.readOnly {
return 0, &os.PathError{Op: "write", Path: f.fileData.name, Err: errors.New("file handle is read only")}
}
n = len(b)
cur := atomic.LoadInt64(&f.at)
f.fileData.Lock()
defer f.fileData.Unlock()
diff := cur - int64(len(f.fileData.data))
diff := off - int64(len(f.fileData.data))
var tail []byte
if n+int(cur) < len(f.fileData.data) {
tail = f.fileData.data[n+int(cur):]
if n+int(off) < len(f.fileData.data) {
tail = f.fileData.data[n+int(off):]
}
if diff > 0 {
f.fileData.data = append(f.fileData.data, append(bytes.Repeat([]byte{0o0}, int(diff)), b...)...)
f.fileData.data = append(f.fileData.data, tail...)
} else {
f.fileData.data = append(f.fileData.data[:cur], b...)
f.fileData.data = append(f.fileData.data[:off], b...)
f.fileData.data = append(f.fileData.data, tail...)
}
setModTime(f.fileData, time.Now())

atomic.AddInt64(&f.at, int64(n))
return
}

func (f *File) WriteAt(b []byte, off int64) (n int, err error) {
atomic.StoreInt64(&f.at, off)
return f.Write(b)
func (f *File) Write(b []byte) (n int, err error) {
n, err = f.WriteAt(b, atomic.LoadInt64(&f.at))
atomic.AddInt64(&f.at, int64(n))
return
}

func (f *File) WriteString(s string) (ret int, err error) {
Expand Down