Roll forward to cl/338482889

Signed-off-by: Alexey Polyudov <apolyudov@google.com>
Change-Id: Ic2bdb234e89f3c5860d1b483dd4bce689f13d057

cpp/platform/api/mutex.h

@@ -0,0 +1,55 @@
+// Copyright 2020 Google LLC
+//
+// 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
+//
+//     https://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.
+
+#ifndef PLATFORM_API_MUTEX_H_
+#define PLATFORM_API_MUTEX_H_
+
+#include "absl/base/thread_annotations.h"
+
+namespace location {
+namespace nearby {
+namespace api {
+
+// A lock is a tool for controlling access to a shared resource by multiple
+// threads.
+//
+// https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/locks/Lock.html
+class ABSL_LOCKABLE Mutex {
+ public:
+  // Mode to pass to implementation constructor.
+  // kRegular        - produces a regular mutex: disallows multiple locks from
+  //                   the same thread; optionally, detects double locks in
+  //                   debug mode.
+  //                   This is the default option.
+  // kRecursive      - produces recursive mutex: allows multiple locks from the
+  //                   same thread.
+  // kRegularNoCheck - produces a regular mutex: disallows double locks,
+  //                   but does not check for deadlocks.
+  enum class Mode {
+    kRegular = 0,
+    kRecursive = 1,
+    kRegularNoCheck = 2,
+  };
+
+  virtual ~Mutex() {}
+
+  virtual void Lock() ABSL_EXCLUSIVE_LOCK_FUNCTION() = 0;
+  virtual void Unlock()  ABSL_UNLOCK_FUNCTION() = 0;
+};
+
+}  // namespace api
+}  // namespace nearby
+}  // namespace location
+
+#endif  // PLATFORM_API_MUTEX_H_