Add PerfLog (#3974)

Add `PerfTime` class representing a point in CPU time and `PerfLogTimer`, used for measuring and logging a time period. Used in `ProjectRenderer::run()

include/PerfLog.h

@@ -0,0 +1,73 @@
+/*
+ * PerfLog.h - Small performance logger
+ *
+ * Copyright (c) 2017-2018 LMMS Developers
+ *
+ * This file is part of LMMS - https://lmms.io
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public
+ * License along with this program (see COPYING); if not, write to the
+ * Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
+ * Boston, MA 02110-1301 USA.
+ *
+ */
+
+#ifndef PERFLOG_H
+#define PERFLOG_H
+
+#include <ctime>
+#include <QtCore/QString>
+
+/// \brief CPU time point
+///
+/// Represents a point in CPU time (not wall-clock time) intended for measuring
+/// performance.
+class PerfTime
+{
+public:
+	PerfTime();
+	bool valid() const;
+
+	clock_t real() const;
+	clock_t user() const;
+	clock_t system() const;
+
+	static PerfTime now();
+	static clock_t ticksPerSecond();
+
+	friend PerfTime operator-(const PerfTime& lhs, const PerfTime& rhs);
+private:
+	clock_t m_real;
+	clock_t m_user;
+	clock_t m_system;
+};
+
+/// \brief The PerfLog class
+///
+/// Measures time between construction and destruction and prints the result to
+/// stderr, along with \p name. Alternatively, call begin() and end() explicitly.
+class PerfLogTimer
+{
+ public:
+	PerfLogTimer(const QString& name);
+	~PerfLogTimer();
+
+	void begin();
+	void end();
+
+ private:
+	QString name;
+	PerfTime begin_time;
+};
+
+#endif