cleanup: move pkg/ to internal/

The internal/ directory in Go has a special meaning, and indicates that
those packages are not meant for external consumption. Ceph-CSI does
provide public APIs for other projects to consume. There is no plan to
keep the API of the internally used packages stable.

Closes: #903
Signed-off-by: Niels de Vos <ndevos@redhat.com>

internal/util/idlocker.go

@@ -0,0 +1,60 @@
+/*
+Copyright 2019 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 util
+
+import (
+	"sync"
+
+	"k8s.io/apimachinery/pkg/util/sets"
+)
+
+const (
+	// VolumeOperationAlreadyExistsFmt string format to return for concurrent operation
+	VolumeOperationAlreadyExistsFmt = "an operation with the given Volume ID %s already exists"
+
+	// SnapshotOperationAlreadyExistsFmt string format to return for concurrent operation
+	SnapshotOperationAlreadyExistsFmt = "an operation with the given Snapshot ID %s already exists"
+)
+
+// VolumeLocks implements a map with atomic operations. It stores a set of all volume IDs
+// with an ongoing operation.
+type VolumeLocks struct {
+	locks sets.String
+	mux   sync.Mutex
+}
+
+// NewVolumeLocks returns new  VolumeLocks
+func NewVolumeLocks() *VolumeLocks {
+	return &VolumeLocks{
+		locks: sets.NewString(),
+	}
+}
+
+// TryAcquire tries to acquire the lock for operating on volumeID and returns true if successful.
+// If another operation is already using volumeID, returns false.
+func (vl *VolumeLocks) TryAcquire(volumeID string) bool {
+	vl.mux.Lock()
+	defer vl.mux.Unlock()
+	if vl.locks.Has(volumeID) {
+		return false
+	}
+	vl.locks.Insert(volumeID)
+	return true
+}
+
+func (vl *VolumeLocks) Release(volumeID string) {
+	vl.mux.Lock()
+	defer vl.mux.Unlock()
+	vl.locks.Delete(volumeID)
+}