VOL-1243: Added logic for thread safety

- Thread safety was added at the proxy level
- Refactored the test init in a base_test structure
- Fixed issue with writing to kv
- Added profiling for locking period

Amendments:

- Comment out a cleanup statement causing KV corruption (as per VOL-1293)
- Added missing license

Change-Id: Id6658270dbb8b738abeef9e9e1d349dce36501bc
diff --git a/db/model/proxy_access_control.go b/db/model/proxy_access_control.go
new file mode 100644
index 0000000..7f4fad5
--- /dev/null
+++ b/db/model/proxy_access_control.go
@@ -0,0 +1,118 @@
+/*
+ * Copyright 2018-present Open Networking Foundation
+
+ * 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 model
+
+import (
+	"github.com/opencord/voltha-go/common/log"
+	"runtime/debug"
+	"sync"
+	"time"
+)
+
+type _singletonProxyAccessControl struct {
+	Cache sync.Map
+}
+
+var _instanceProxyAccessControl *_singletonProxyAccessControl
+var _onceProxyAccessControl sync.Once
+
+func GetProxyAccessControl() *_singletonProxyAccessControl {
+	_onceProxyAccessControl.Do(func() {
+		_instanceProxyAccessControl = &_singletonProxyAccessControl{}
+	})
+	return _instanceProxyAccessControl
+}
+
+type ProxyAccessControl interface {
+	Get(path string, depth int, deep bool, txid string, control bool) interface{}
+	Update(path string, data interface{}, strict bool, txid string, control bool) interface{}
+	Add(path string, data interface{}, txid string, control bool) interface{}
+	Remove(path string, txid string, control bool) interface{}
+}
+
+type proxyAccessControl struct {
+	//sync.Mutex
+	Proxy    *Proxy
+	PathLock chan struct{}
+	Path     string
+
+	start time.Time
+	stop  time.Time
+}
+
+func NewProxyAccessControl(proxy *Proxy, path string) ProxyAccessControl {
+	return &proxyAccessControl{
+		Proxy:    proxy,
+		Path:     path,
+		PathLock: make(chan struct{}, 1),
+	}
+}
+
+func (pac *proxyAccessControl) lock() {
+	log.CleanUp()
+	log.Debugf("Before lock ... pac: %+v, stack = %s", pac, string(debug.Stack()))
+	pac.PathLock <- struct{}{}
+	pac.start = time.Now()
+	log.Debugf("Got lock ... pac: %+v, stack = %s", pac, string(debug.Stack()))
+	//time.Sleep(1 * time.Second)
+	log.Debugf("<<<<< %s >>>>>> locked, stack=%s", pac.Path, string(debug.Stack()))
+}
+func (pac *proxyAccessControl) unlock() {
+	log.CleanUp()
+	log.Debugf("Before unlock ... pac: %+v, stack = %s", pac, string(debug.Stack()))
+	<-pac.PathLock
+	pac.stop = time.Now()
+	GetProfiling().AddToInMemoryLockTime(pac.stop.Sub(pac.start).Seconds())
+	log.Debugf("Got unlock ... pac: %+v, stack = %s", pac, string(debug.Stack()))
+	log.Debugf("<<<<< %s >>>>>> unlocked, stack=%s", pac.Path, string(debug.Stack()))
+}
+
+func (pac *proxyAccessControl) Get(path string, depth int, deep bool, txid string, control bool) interface{} {
+	if control {
+		pac.lock()
+		defer pac.unlock()
+		log.Debugf("controlling get, stack = %s", string(debug.Stack()))
+	}
+	pac.Proxy.Root.Proxy = pac.Proxy
+	return pac.Proxy.Root.Get(path, "", depth, deep, txid)
+}
+func (pac *proxyAccessControl) Update(path string, data interface{}, strict bool, txid string, control bool) interface{} {
+	if control {
+		pac.lock()
+		defer pac.unlock()
+		log.Debugf("controlling update, stack = %s", string(debug.Stack()))
+	}
+	pac.Proxy.Root.Proxy = pac.Proxy
+	return pac.Proxy.Root.Update(path, data, strict, txid, nil)
+}
+func (pac *proxyAccessControl) Add(path string, data interface{}, txid string, control bool) interface{} {
+	if control {
+		pac.lock()
+		defer pac.unlock()
+		log.Debugf("controlling add, stack = %s", string(debug.Stack()))
+	}
+	pac.Proxy.Root.Proxy = pac.Proxy
+	return pac.Proxy.Root.Add(path, data, txid, nil)
+}
+func (pac *proxyAccessControl) Remove(path string, txid string, control bool) interface{} {
+	if control {
+		pac.lock()
+		defer pac.unlock()
+		log.Debugf("controlling remove, stack = %s", string(debug.Stack()))
+	}
+	pac.Proxy.Root.Proxy = pac.Proxy
+	return pac.Proxy.Root.Remove(path, txid, nil)
+}