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// Copyright 2015 The etcd Authors
//
// 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.
// +build windows
package fileutil
import (
"errors"
"fmt"
"os"
"syscall"
"unsafe"
)
var (
modkernel32 = syscall.NewLazyDLL("kernel32.dll")
procLockFileEx = modkernel32.NewProc("LockFileEx")
errLocked = errors.New("The process cannot access the file because another process has locked a portion of the file.")
)
const (
// https://msdn.microsoft.com/en-us/library/windows/desktop/aa365203(v=vs.85).aspx
LOCKFILE_EXCLUSIVE_LOCK = 2
LOCKFILE_FAIL_IMMEDIATELY = 1
// see https://msdn.microsoft.com/en-us/library/windows/desktop/ms681382(v=vs.85).aspx
errLockViolation syscall.Errno = 0x21
)
func TryLockFile(path string, flag int, perm os.FileMode) (*LockedFile, error) {
f, err := open(path, flag, perm)
if err != nil {
return nil, err
}
if err := lockFile(syscall.Handle(f.Fd()), LOCKFILE_FAIL_IMMEDIATELY); err != nil {
f.Close()
return nil, err
}
return &LockedFile{f}, nil
}
func LockFile(path string, flag int, perm os.FileMode) (*LockedFile, error) {
f, err := open(path, flag, perm)
if err != nil {
return nil, err
}
if err := lockFile(syscall.Handle(f.Fd()), 0); err != nil {
f.Close()
return nil, err
}
return &LockedFile{f}, nil
}
func open(path string, flag int, perm os.FileMode) (*os.File, error) {
if path == "" {
return nil, fmt.Errorf("cannot open empty filename")
}
var access uint32
switch flag {
case syscall.O_RDONLY:
access = syscall.GENERIC_READ
case syscall.O_WRONLY:
access = syscall.GENERIC_WRITE
case syscall.O_RDWR:
access = syscall.GENERIC_READ | syscall.GENERIC_WRITE
case syscall.O_WRONLY | syscall.O_CREAT:
access = syscall.GENERIC_ALL
default:
panic(fmt.Errorf("flag %v is not supported", flag))
}
fd, err := syscall.CreateFile(&(syscall.StringToUTF16(path)[0]),
access,
syscall.FILE_SHARE_READ|syscall.FILE_SHARE_WRITE|syscall.FILE_SHARE_DELETE,
nil,
syscall.OPEN_ALWAYS,
syscall.FILE_ATTRIBUTE_NORMAL,
0)
if err != nil {
return nil, err
}
return os.NewFile(uintptr(fd), path), nil
}
func lockFile(fd syscall.Handle, flags uint32) error {
var flag uint32 = LOCKFILE_EXCLUSIVE_LOCK
flag |= flags
if fd == syscall.InvalidHandle {
return nil
}
err := lockFileEx(fd, flag, 1, 0, &syscall.Overlapped{})
if err == nil {
return nil
} else if err.Error() == errLocked.Error() {
return ErrLocked
} else if err != errLockViolation {
return err
}
return nil
}
func lockFileEx(h syscall.Handle, flags, locklow, lockhigh uint32, ol *syscall.Overlapped) (err error) {
var reserved uint32 = 0
r1, _, e1 := syscall.Syscall6(procLockFileEx.Addr(), 6, uintptr(h), uintptr(flags), uintptr(reserved), uintptr(locklow), uintptr(lockhigh), uintptr(unsafe.Pointer(ol)))
if r1 == 0 {
if e1 != 0 {
err = error(e1)
} else {
err = syscall.EINVAL
}
}
return err
}