vendor: add buildkit

Signed-off-by: Tonis Tiigi <tonistiigi@gmail.com>

vendor/github.com/gofrs/flock/flock_windows.go

@@ -0,0 +1,140 @@
+// 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
+		}
+	}
+
+	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
+		}
+	}
+
+	_, 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
+}