// 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. package flock import ( "syscall" ) // ErrorLockViolation is the error code returned from the Windows syscall when a // lock would block and you ask to fail immediately. const ErrorLockViolation syscall.Errno = 0x21 // 33 // 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 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, winLockfileExclusiveLock) } // RLock is a blocking call to try and take a shared 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 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, winLockfileSharedLock) } func (f *Flock) lock(locked *bool, flag uint32) error { f.m.Lock() defer f.m.Unlock() if *locked { return nil } if f.fh == nil { if err := f.setFh(); err != nil { return err } defer f.ensureFhState() } if _, errNo := lockFileEx(syscall.Handle(f.fh.Fd()), flag, 0, 1, 0, &syscall.Overlapped{}); errNo > 0 { return errNo } *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 // UnlockFileEx() 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 _, errNo := unlockFileEx(syscall.Handle(f.fh.Fd()), 0, 1, 0, &syscall.Overlapped{}); errNo > 0 { return errNo } 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 does take a 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, winLockfileExclusiveLock) } // TryRLock is the preferred function for taking a shared file lock. This // function does take a 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 shared-locked. func (f *Flock) TryRLock() (bool, error) { return f.try(&f.r, winLockfileSharedLock) } func (f *Flock) try(locked *bool, flag uint32) (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 } defer f.ensureFhState() } _, errNo := lockFileEx(syscall.Handle(f.fh.Fd()), flag|winLockfileFailImmediately, 0, 1, 0, &syscall.Overlapped{}) if errNo > 0 { if errNo == ErrorLockViolation || errNo == syscall.ERROR_IO_PENDING { return false, nil } return false, errNo } *locked = true return true, nil }