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// Copyright 2016 Canonical Ltd.
// Licensed under the LGPLv3, see LICENCE file for details.
// +build darwin dragonfly freebsd linux netbsd openbsd
package fslock
import (
"syscall"
"time"
)
// Lock implements cross-process locks using syscalls.
// This implementation is based on flock syscall.
type Lock struct {
filename string
fd int
}
// New returns a new lock around the given file.
func New(filename string) *Lock {
return &Lock{filename: filename}
}
// Lock locks the lock. This call will block until the lock is available.
func (l *Lock) Lock() error {
if err := l.open(); err != nil {
return err
}
return syscall.Flock(l.fd, syscall.LOCK_EX)
}
// TryLock attempts to lock the lock. This method will return ErrLocked
// immediately if the lock cannot be acquired.
func (l *Lock) TryLock() error {
if err := l.open(); err != nil {
return err
}
err := syscall.Flock(l.fd, syscall.LOCK_EX|syscall.LOCK_NB)
if err != nil {
syscall.Close(l.fd)
}
if err == syscall.EWOULDBLOCK {
return ErrLocked
}
return err
}
func (l *Lock) open() error {
fd, err := syscall.Open(l.filename, syscall.O_CREAT|syscall.O_RDONLY, 0600)
if err != nil {
return err
}
l.fd = fd
return nil
}
// Unlock unlocks the lock.
func (l *Lock) Unlock() error {
return syscall.Close(l.fd)
}
// LockWithTimeout tries to lock the lock until the timeout expires. If the
// timeout expires, this method will return ErrTimeout.
func (l *Lock) LockWithTimeout(timeout time.Duration) error {
if err := l.open(); err != nil {
return err
}
result := make(chan error)
cancel := make(chan struct{})
go func() {
err := syscall.Flock(l.fd, syscall.LOCK_EX)
select {
case <-cancel:
// Timed out, cleanup if necessary.
syscall.Flock(l.fd, syscall.LOCK_UN)
syscall.Close(l.fd)
case result <- err:
}
}()
select {
case err := <-result:
return err
case <-time.After(timeout):
close(cancel)
return ErrTimeout
}
}
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