internal: add missing Mutex.h header

thermion_dart/native/include/filament/utils/linux/Mutex.h

@@ -0,0 +1,66 @@
+/*
+ * Copyright (C) 2016 The Android Open Source Project
+ *
+ * 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.
+ */
+
+#ifndef TNT_UTILS_LINUX_MUTEX_H
+#define TNT_UTILS_LINUX_MUTEX_H
+
+#include <utils/compiler.h>
+
+#include <atomic>
+
+#include <stdint.h>
+
+namespace utils {
+
+/*
+ * A very simple mutex class that can be used as an (almost) drop-in replacement
+ * for std::mutex.
+ * It is very low overhead as most of it is inlined.
+ */
+
+class Mutex {
+public:
+    constexpr Mutex() noexcept = default;
+    Mutex(const Mutex&) = delete;
+    Mutex& operator=(const Mutex&) = delete;
+
+    void lock() noexcept {
+        uint32_t old_state = UNLOCKED;
+        if (UTILS_UNLIKELY(!mState.compare_exchange_strong(old_state,
+                LOCKED, std::memory_order_acquire, std::memory_order_relaxed))) {
+            wait();
+        }
+    }
+
+    void unlock() noexcept {
+        if (UTILS_UNLIKELY(mState.exchange(UNLOCKED, std::memory_order_release) == LOCKED_CONTENDED)) {
+            wake();
+        }
+    }
+
+private:
+    enum {
+        UNLOCKED = 0, LOCKED = 1, LOCKED_CONTENDED = 2
+    };
+    std::atomic<uint32_t> mState = { UNLOCKED };
+
+    void wait() noexcept;
+    void wake() noexcept;
+};
+
+} // namespace utils
+
+#endif // TNT_UTILS_LINUX_MUTEX_H