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flock_unix.go
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flock_unix.go
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// Copyright 2015 Tim Heckman. All rights reserved.
// Use of this source code is governed by the BSD 3-Clause
// license that can be found in the LICENSE file.
// +build !windows
package flock
import (
"syscall"
)
// Lock is a blocking call to try and take an exclusive file lock. It will wait
// until it is able to obtain the exclusive file lock. It's recommended that
// TryLock() be used over this function. This function may block the ability to
// query the current Locked() or RLocked() status due to a RW-mutex lock.
//
// If we are already exclusive-locked, this function short-circuits and returns
// immediately assuming it can take the mutex lock.
func (f *Flock) Lock() error {
return f.lock(&f.l, syscall.LOCK_EX)
}
// RLock is a blocking call to try and take a ahred file lock. It will wait
// until it is able to obtain the shared file lock. It's recommended that
// TryRLock() be used over this function. This function may block the ability to
// query the current Locked() or RLocked() status due to a RW-mutex lock.
//
// If we are already shared-locked, this function short-circuits and returns
// immediately assuming it can take the mutex lock.
func (f *Flock) RLock() error {
return f.lock(&f.r, syscall.LOCK_SH)
}
func (f *Flock) lock(locked *bool, flag int) error {
f.m.Lock()
defer f.m.Unlock()
if *locked {
return nil
}
if f.fh == nil {
if err := f.setFh(); err != nil {
return err
}
}
if err := syscall.Flock(int(f.fh.Fd()), flag); err != nil {
return err
}
*locked = true
return nil
}
// Unlock is a function to unlock the file. This file takes a RW-mutex lock, so
// while it is running the Locked() and RLocked() functions will be blocked.
//
// This function short-circuits if we are unlocked already. If not, it calls
// syscall.LOCK_UN on the file and closes the file descriptor. It does not
// remove the file from disk. It's up to your application to do.
func (f *Flock) Unlock() error {
f.m.Lock()
defer f.m.Unlock()
// if we aren't locked or if the lockfile instance is nil
// just return a nil error because we are unlocked
if (!f.l && !f.r) || f.fh == nil {
return nil
}
// mark the file as unlocked
if err := syscall.Flock(int(f.fh.Fd()), syscall.LOCK_UN); err != nil {
return err
}
f.fh.Close()
f.l = false
f.r = false
f.fh = nil
return nil
}
// TryLock is the preferred function for taking an exclusive file lock. This
// function takes an RW-mutex lock before it tries to lock the file, so there is
// the possibility that this function may block for a short time if another
// goroutine is trying to take any action.
//
// The actual file lock is non-blocking. If we are unable to get the exclusive
// file lock, the function will return false instead of waiting for the lock. If
// we get the lock, we also set the *Flock instance as being exclusive-locked.
func (f *Flock) TryLock() (bool, error) {
return f.try(&f.l, syscall.LOCK_EX)
}
// TryRLock is the preferred function for taking a shared file lock. This
// function takes an RW-mutex lock before it tries to lock the file, so there is
// the possibility that this function may block for a short time if another
// goroutine is trying to take any action.
//
// The actual file lock is non-blocking. If we are unable to get the shared file
// lock, the function will return false instead of waiting for the lock. If we
// get the lock, we also set the *Flock instance as being share-locked.
func (f *Flock) TryRLock() (bool, error) {
return f.try(&f.r, syscall.LOCK_SH)
}
func (f *Flock) try(locked *bool, flag int) (bool, error) {
f.m.Lock()
defer f.m.Unlock()
if *locked {
return true, nil
}
if f.fh == nil {
if err := f.setFh(); err != nil {
return false, err
}
}
err := syscall.Flock(int(f.fh.Fd()), flag|syscall.LOCK_NB)
switch err {
case syscall.EWOULDBLOCK:
return false, nil
case nil:
*locked = true
return true, nil
}
return false, err
}