kubelet: add a pidfile

pkg/util/flock/flock_unix.go

@@ -0,0 +1,51 @@
+// +build linux darwin freebsd openbsd netbsd dragonfly
+
+/*
+Copyright 2016 The Kubernetes Authors All rights reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package flock
+
+import (
+	"os"
+	"sync"
+
+	"golang.org/x/sys/unix"
+)
+
+var (
+	// lock guards lockfile. Assignment is not atomic.
+	lock sync.Mutex
+	// os.File has a runtime.Finalizer so the fd will be closed if the struct
+	// is garbage collected. Let's hold onto a reference so that doesn't happen.
+	lockfile *os.File
+)
+
+// Acquire acquires a lock on a file for the duration of the process. This method
+// is reentrant.
+func Acquire(path string) error {
+	lock.Lock()
+	defer lock.Unlock()
+	var err error
+	if lockfile, err = os.OpenFile(path, os.O_RDWR|os.O_CREATE, 0600); err != nil {
+		return err
+	}
+
+	opts := unix.Flock_t{Type: unix.F_WRLCK}
+	if err := unix.FcntlFlock(lockfile.Fd(), unix.F_SETLKW, &opts); err != nil {
+		return err
+	}
+	return nil
+}