Common: Add a 'Flag' class that is used to encapsulate a boolean flag manipulated from several threads

Source/UnitTests/Common/FlagTest.cpp

@@ -0,0 +1,60 @@
+// Copyright 2014 Dolphin Emulator Project
+// Licensed under GPLv2
+// Refer to the license.txt file included.
+
+#include <gtest/gtest.h>
+#include <thread>
+
+#include "Common/Flag.h"
+
+using Common::Flag;
+
+TEST(Flag, Simple)
+{
+	Flag f;
+	EXPECT_FALSE(f.IsSet());
+
+	f.Set();
+	EXPECT_TRUE(f.IsSet());
+
+	f.Clear();
+	EXPECT_FALSE(f.IsSet());
+
+	f.Set(false);
+	EXPECT_FALSE(f.IsSet());
+
+	Flag f2(true);
+	EXPECT_TRUE(f2.IsSet());
+}
+
+TEST(Flag, MultiThreaded)
+{
+	Flag f;
+	int count = 0;
+	const int ITERATIONS_COUNT = 100000;
+
+	auto setter = [&f]() {
+		for (int i = 0; i < ITERATIONS_COUNT; ++i)
+		{
+			while (f.IsSet());
+			f.Set();
+		}
+	};
+
+	auto clearer = [&f, &count]() {
+		for (int i = 0; i < ITERATIONS_COUNT; ++i)
+		{
+			while (!f.IsSet());
+			count++;
+			f.Clear();
+		}
+	};
+
+	std::thread setter_thread(setter);
+	std::thread clearer_thread(clearer);
+
+	setter_thread.join();
+	clearer_thread.join();
+
+	EXPECT_EQ(ITERATIONS_COUNT, count);
+}