Roll forward to cl/314747126

Signed-off-by: Alexey Polyudov <apolyudov@google.com>
Change-Id: Ie19e006429b138b3768e97dae971a43fdc5ef8bf

cpp/platform/impl/g3/atomic_reference_impl.h

@@ -0,0 +1,52 @@
+// 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_IMPL_G3_ATOMIC_REFERENCE_IMPL_H_
+#define PLATFORM_IMPL_G3_ATOMIC_REFERENCE_IMPL_H_
+
+#include "platform/api/atomic_reference.h"
+#include "platform/ptr.h"
+#include "absl/synchronization/mutex.h"
+#include "absl/types/any.h"
+
+namespace location {
+namespace nearby {
+namespace platform {
+
+// Provide implementation for absl::any.
+class AtomicReferenceImpl : public AtomicReference<absl::any> {
+ public:
+  explicit AtomicReferenceImpl(absl::any initial_value)
+      : value_(std::move(initial_value)) {}
+  ~AtomicReferenceImpl() override = default;
+
+  absl::any get() override {
+    absl::MutexLock lock(&mutex_);
+    return value_;
+  }
+  void set(absl::any value) override {
+    absl::MutexLock lock(&mutex_);
+    value_ = std::move(value);
+  }
+
+ private:
+  absl::Mutex mutex_;
+  absl::any value_;
+};
+
+}  // namespace platform
+}  // namespace nearby
+}  // namespace location
+
+#endif  // PLATFORM_IMPL_G3_ATOMIC_REFERENCE_IMPL_H_