pkg/fileutil: clean up interface, comments

pkg/fileutil/lock.go

@@ -0,0 +1,29 @@
+// Copyright 2016 CoreOS, Inc.
+//
+// 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 fileutil
+
+type Lock interface {
+	// Name returns the name of the file.
+	Name() string
+	// TryLock acquires exclusivity on the lock without blocking.
+	TryLock() error
+	// Lock acquires exclusivity on the lock.
+	Lock() error
+	// Unlock unlocks the lock.
+	Unlock() error
+	// Destroy should be called after Unlock to clean up
+	// the resources.
+	Destroy() error
+}