Roll forward to cl/338482889

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

cpp/platform/impl/shared/posix_mutex.h

@@ -0,0 +1,45 @@
+// 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_SHARED_POSIX_MUTEX_H_
+#define PLATFORM_IMPL_SHARED_POSIX_MUTEX_H_
+
+#include <pthread.h>
+
+#include "platform/api/mutex.h"
+
+namespace location {
+namespace nearby {
+namespace posix {
+
+class ABSL_LOCKABLE Mutex : public api::Mutex {
+ public:
+  Mutex();
+  ~Mutex() override;
+
+  void Lock() ABSL_EXCLUSIVE_LOCK_FUNCTION() override;
+  void Unlock() ABSL_UNLOCK_FUNCTION() override;
+
+ private:
+  friend class ConditionVariable;
+
+  pthread_mutexattr_t attr_;
+  pthread_mutex_t mutex_;
+};
+
+}  // namespace posix
+}  // namespace nearby
+}  // namespace location
+
+#endif  // PLATFORM_IMPL_SHARED_POSIX_MUTEX_H_