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// Copyright (c) 2018-2021, Sylabs Inc. All rights reserved.
// This software is licensed under a 3-clause BSD license. Please consult the
// LICENSE file distributed with the sources of this project regarding your
// rights to use or distribute this software.
package lock
import (
"errors"
"io"
"os"
"golang.org/x/sys/unix"
)
// Exclusive applies an exclusive lock on path
func Exclusive(path string) (fd int, err error) {
fd, err = unix.Open(path, os.O_RDONLY, 0)
if err != nil {
return fd, err
}
err = unix.Flock(fd, unix.LOCK_EX)
if err != nil {
unix.Close(fd)
return fd, err
}
return fd, nil
}
// Release removes a lock on path referenced by fd
func Release(fd int) error {
defer unix.Close(fd)
return unix.Flock(fd, unix.LOCK_UN)
}
// ErrByteRangeAcquired corresponds to the error returned
// when a file byte-range is already acquired.
var ErrByteRangeAcquired = errors.New("file byte-range lock is already acquired")
// ErrLockNotSupported corresponds to the error returned
// when file locking is not supported.
var ErrLockNotSupported = errors.New("file lock is not supported")
// ByteRange defines a file byte-range lock.
type ByteRange struct {
fd int
start int64
len int64
}
// NewByteRange returns a file byte-range lock.
func NewByteRange(fd int, start, len int64) *ByteRange {
return &ByteRange{fd, start, len}
}
// flock places a byte-range lock.
func (r *ByteRange) flock(lockType int16) error {
lk := &unix.Flock_t{
Type: lockType,
Whence: io.SeekStart,
Start: r.start,
Len: r.len,
}
err := unix.FcntlFlock(uintptr(r.fd), setLk, lk)
if err == unix.EAGAIN || err == unix.EACCES {
return ErrByteRangeAcquired
} else if err == unix.ENOLCK {
return ErrLockNotSupported
}
return err
}
// Lock places a write lock for the corresponding byte-range.
func (r *ByteRange) Lock() error {
return r.flock(unix.F_WRLCK)
}
// RLock places a read lock for the corresponding byte-range.
func (r *ByteRange) RLock() error {
return r.flock(unix.F_RDLCK)
}
// Unlock removes the lock for the corresponding byte-range.
func (r *ByteRange) Unlock() error {
return r.flock(unix.F_UNLCK)
}
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