Add flock from k8s.io/kubernetes/pkg/util/flock

pkg/flock/flock_other.go

+// +build !linux,!darwin,!freebsd,!openbsd,!netbsd,!dragonfly
+
+/*
+Copyright 2016 The Kubernetes Authors.
+
+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
+
+// Acquire is not implemented on non-unix systems.
+func Acquire(path string) error {
+	return nil
+}

pkg/flock/flock_unix.go

+// +build linux darwin freebsd openbsd netbsd dragonfly
+
+/*
+Copyright 2016 The Kubernetes Authors.
+
+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 "golang.org/x/sys/unix"
+
+// Acquire acquires a lock on a file for the duration of the process. This method
+// is reentrant.
+func Acquire(path string) error {
+	fd, err := unix.Open(path, unix.O_CREAT|unix.O_RDWR|unix.O_CLOEXEC, 0600)
+	if err != nil {
+		return err
+	}
+
+	// We don't need to close the fd since we should hold
+	// it until the process exits.
+
+	return unix.Flock(fd, unix.LOCK_EX)
+}