rewrite checkpoint

vendor/github.com/theckman/go-flock/flock.go

@@ -0,0 +1,61 @@
+// 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.
+package flock
+
+import (
+	"os"
+	"sync"
+)
+
+// 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
+}
+
+// NewFlock is a function to return a new instance of *Flock. The only parameter
+// it takes is the path to the desired lockfile.
+func NewFlock(path string) *Flock {
+	return &Flock{path: path}
+}
+
+// Path is a function to return the path as provided in NewFlock().
+func (f *Flock) Path() string {
+	return f.path
+}
+
+// Locked is a function to return the current lock state (locked: true, unlocked: false).
+func (f *Flock) Locked() bool {
+	f.m.RLock()
+	defer f.m.RUnlock()
+	return f.l
+}
+
+func (f *Flock) String() string {
+	return f.path
+}
+
+func (f *Flock) setFh() error {
+	// open a new os.File instance
+	// create it if it doesn't exist, truncate it if it does exist, open the file read-write
+	fh, err := os.OpenFile(f.path, os.O_CREATE|os.O_TRUNC|os.O_RDWR, os.FileMode(0600))
+
+	if err != nil {
+		return err
+	}
+
+	// set the filehandle on the struct
+	f.fh = fh
+	return nil
+}