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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.
-
- 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
- }
|