go lockedfile_filelock 源码
golang lockedfile_filelock 代码
文件路径：/src/cmd/go/internal/lockedfile/lockedfile_filelock.go
// Copyright 2018 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
//go:build !plan9
package lockedfile
import (
"io/fs"
"os"
"cmd/go/internal/lockedfile/internal/filelock"
)
func openFile(name string, flag int, perm fs.FileMode) (*os.File, error) {
// On BSD systems, we could add the O_SHLOCK or O_EXLOCK flag to the OpenFile
// call instead of locking separately, but we have to support separate locking
// calls for Linux and Windows anyway, so it's simpler to use that approach
// consistently.
f, err := os.OpenFile(name, flag&^os.O_TRUNC, perm)
if err != nil {
return nil, err
}
switch flag & (os.O_RDONLY | os.O_WRONLY | os.O_RDWR) {
case os.O_WRONLY, os.O_RDWR:
err = filelock.Lock(f)
default:
err = filelock.RLock(f)
}
if err != nil {
f.Close()
return nil, err
}
if flag&os.O_TRUNC == os.O_TRUNC {
if err := f.Truncate(0); err != nil {
// The documentation for os.O_TRUNC says “if possible, truncate file when
// opened”, but doesn't define “possible” (golang.org/issue/28699).
// We'll treat regular files (and symlinks to regular files) as “possible”
// and ignore errors for the rest.
if fi, statErr := f.Stat(); statErr != nil || fi.Mode().IsRegular() {
filelock.Unlock(f)
f.Close()
return nil, err
}
}
}
return f, nil
}
func closeFile(f *os.File) error {
// Since locking syscalls operate on file descriptors, we must unlock the file
// while the descriptor is still valid — that is, before the file is closed —
// and avoid unlocking files that are already closed.
err := filelock.Unlock(f)
if closeErr := f.Close(); err == nil {
err = closeErr
}
return err
}
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