vendor: add buildkit

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

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

@@ -0,0 +1,127 @@
+// 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 implements a thread-safe sync.Locker interface for file locking.
+// It also includes a non-blocking TryLock() function to allow locking
+// without blocking execution.
+//
+// Package flock is released under the BSD 3-Clause License. See the LICENSE file
+// for more details.
+//
+// While using this library, remember that the locking behaviors are not
+// guaranteed to be the same on each platform. For example, some UNIX-like
+// operating systems will transparently convert a shared lock to an exclusive
+// lock. If you Unlock() the flock from a location where you believe that you
+// have the shared lock, you may accidently drop the exclusive lock.
+package flock
+
+import (
+	"context"
+	"os"
+	"sync"
+	"time"
+)
+
+// Flock is the struct type to handle file locking. All fields are unexported,
+// with access to some of the fields provided by getter methods (Path() and Locked()).
+type Flock struct {
+	path string
+	m    sync.RWMutex
+	fh   *os.File
+	l    bool
+	r    bool
+}
+
+// New returns a new instance of *Flock. The only parameter
+// it takes is the path to the desired lockfile.
+func New(path string) *Flock {
+	return &Flock{path: path}
+}
+
+// NewFlock returns a new instance of *Flock. The only parameter
+// it takes is the path to the desired lockfile.
+//
+// Deprecated: Use New instead.
+func NewFlock(path string) *Flock {
+	return New(path)
+}
+
+// Close is equivalent to calling Unlock.
+//
+// This will release the lock and close the underlying file descriptor.
+// It will not remove the file from disk, that's up to your application.
+func (f *Flock) Close() error {
+	return f.Unlock()
+}
+
+// Path returns the path as provided in NewFlock().
+func (f *Flock) Path() string {
+	return f.path
+}
+
+// Locked returns the lock state (locked: true, unlocked: false).
+//
+// Warning: by the time you use the returned value, the state may have changed.
+func (f *Flock) Locked() bool {
+	f.m.RLock()
+	defer f.m.RUnlock()
+	return f.l
+}
+
+// RLocked returns the read lock state (locked: true, unlocked: false).
+//
+// Warning: by the time you use the returned value, the state may have changed.
+func (f *Flock) RLocked() bool {
+	f.m.RLock()
+	defer f.m.RUnlock()
+	return f.r
+}
+
+func (f *Flock) String() string {
+	return f.path
+}
+
+// TryLockContext repeatedly tries to take an exclusive lock until one of the
+// conditions is met: TryLock succeeds, TryLock fails with error, or Context
+// Done channel is closed.
+func (f *Flock) TryLockContext(ctx context.Context, retryDelay time.Duration) (bool, error) {
+	return tryCtx(f.TryLock, ctx, retryDelay)
+}
+
+// TryRLockContext repeatedly tries to take a shared lock until one of the
+// conditions is met: TryRLock succeeds, TryRLock fails with error, or Context
+// Done channel is closed.
+func (f *Flock) TryRLockContext(ctx context.Context, retryDelay time.Duration) (bool, error) {
+	return tryCtx(f.TryRLock, ctx, retryDelay)
+}
+
+func tryCtx(fn func() (bool, error), ctx context.Context, retryDelay time.Duration) (bool, error) {
+	if ctx.Err() != nil {
+		return false, ctx.Err()
+	}
+	for {
+		if ok, err := fn(); ok || err != nil {
+			return ok, err
+		}
+		select {
+		case <-ctx.Done():
+			return false, ctx.Err()
+		case <-time.After(retryDelay):
+			// try again
+		}
+	}
+}
+
+func (f *Flock) setFh() error {
+	// open a new os.File instance
+	// create it if it doesn't exist, and open the file read-only.
+	fh, err := os.OpenFile(f.path, os.O_CREATE|os.O_RDONLY, os.FileMode(0600))
+	if err != nil {
+		return err
+	}
+
+	// set the filehandle on the struct
+	f.fh = fh
+	return nil
+}