Add class PerformanceStopWatch.

src/common/PerformanceStopWatch.h

@@ -0,0 +1,93 @@
+/*
+ *  The contents of this file are subject to the Initial
+ *  Developer's Public License Version 1.0 (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.ibphoenix.com/main.nfs?a=ibphoenix&page=ibp_idpl.
+ *
+ *  Software distributed under the License is distributed AS IS,
+ *  WITHOUT WARRANTY OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing rights
+ *  and limitations under the License.
+ *
+ *  The Original Code was created by Adriano dos Santos Fernandes
+ *  for the Firebird Open Source RDBMS project.
+ *
+ *  Copyright (c) 2023 Adriano dos Santos Fernandes <adrianosf@gmail.com>
+ *  and all contributors signed below.
+ *
+ *  All Rights Reserved.
+ *  Contributor(s): ______________________________________.
+ */
+
+#ifndef COMMON_PERFORMANCE_STOP_WATCH_H
+#define COMMON_PERFORMANCE_STOP_WATCH_H
+
+#include "../common/utils_proto.h"
+
+
+namespace Firebird
+{
+
+// This class is a wrapper to fb_utils::query_performance_counter() with a way to let
+// the caller amortize timings expended in that function calls.
+// This class is not thread-safe.
+class PerformanceStopWatch
+{
+public:
+	PerformanceStopWatch() = default;
+	PerformanceStopWatch(const PerformanceStopWatch&) = delete;
+	PerformanceStopWatch& operator=(const PerformanceStopWatch&) = delete;
+
+public:
+	SINT64 queryTicks()
+	{
+		const auto initialTicks = fb_utils::query_performance_counter();
+
+		if ((initialTicks - lastMeasuredTicks) * 1000 / fb_utils::query_performance_frequency() >
+				OVERHEAD_CALC_FREQUENCY_MS)
+		{
+			const auto currentTicks = lastMeasuredTicks = fb_utils::query_performance_counter();
+			lastOverhead = currentTicks - initialTicks;
+			accumulatedOverhead += lastOverhead + lastOverhead;
+			return currentTicks;
+		}
+		else
+		{
+			accumulatedOverhead += lastOverhead;
+			return initialTicks;
+		}
+	}
+
+	SINT64 getAccumulatedOverhead() const
+	{
+		return accumulatedOverhead;
+	}
+
+	SINT64 getElapsedTicksAndAdjustOverhead(SINT64 currentTicks, SINT64 previousTicks,
+		SINT64 previousAccumulatedOverhead)
+	{
+		const SINT64 overhead = MAX(accumulatedOverhead - previousAccumulatedOverhead, 0);
+		const SINT64 elapsedTicks = currentTicks - previousTicks - overhead;
+
+		if (elapsedTicks >= 0)
+			return elapsedTicks;
+
+		accumulatedOverhead += elapsedTicks;
+
+		return 0;
+	}
+
+public:
+	static constexpr SINT64 OVERHEAD_CALC_FREQUENCY_MS = 30 * 1000;
+
+private:
+	SINT64 lastMeasuredTicks = 0;
+	SINT64 lastOverhead = 0;
+	SINT64 accumulatedOverhead = 0;
+};
+
+}	// namespace Firebird
+
+
+#endif	// COMMON_PERFORMANCE_STOP_WATCH_H