Codechange: introduce a framework for all our timers

IntervalTimer and TimeoutTimer use RAII, and can be used to replace
all the time-based timeouts, lag-detection, "execute every N" we
have.
As it uses RAII, you can safely use it as static variable, class
member, temporary variable, etc. As soon as it goes out-of-scope,
it will be safely removed.
This allows for much easier to read code when it comes to intervals.

src/timer/timer_manager.h

@@ -0,0 +1,86 @@
+/*
+ * This file is part of OpenTTD.
+ * OpenTTD 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, version 2.
+ * OpenTTD 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 OpenTTD. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+/** @file timer_manager.h Definition of the TimerManager */
+/** @note don't include this file; include "timer.h". */
+
+#ifndef TIMER_MANAGER_H
+#define TIMER_MANAGER_H
+
+#include "stdafx.h"
+
+#include <set>
+
+template <typename TTimerType>
+class BaseTimer;
+
+/**
+ * The TimerManager manages a single Timer-type.
+ *
+ * It allows for automatic registration and unregistration of timers like Interval and OneShot.
+ *
+ * Each Timer-type needs to implement the Elapsed() method, and distribute that to the timers if needed.
+ */
+template <typename TTimerType>
+class TimerManager {
+public:
+	using TElapsed = typename TTimerType::TElapsed;
+
+	/* Avoid copying this object; it is a singleton object. */
+	TimerManager(TimerManager const &) = delete;
+	TimerManager &operator=(TimerManager const &) = delete;
+
+	/**
+	 * Register a timer.
+	 *
+	 * @param timer The timer to register.
+	 */
+	static void RegisterTimer(BaseTimer<TTimerType> &timer) {
+		GetTimers().insert(&timer);
+	}
+
+	/**
+	 * Unregister a timer.
+	 *
+	 * @param timer The timer to unregister.
+	 */
+	static void UnregisterTimer(BaseTimer<TTimerType> &timer) {
+		GetTimers().erase(&timer);
+	}
+
+	/**
+	 * Called when time for this timer elapsed.
+	 *
+	 * The implementation per type is different, but they all share a similar goal:
+	 *   Call the Elapsed() method of all active timers.
+	 *
+	 * @param value The amount of time that has elapsed.
+	 */
+	static void Elapsed(TElapsed value);
+
+private:
+	/**
+	 * Sorter for timers.
+	 *
+	 * It will sort based on the period, smaller first. If the period is the
+	 * same, it will sort based on the pointer value.
+	 */
+	struct base_timer_sorter {
+		bool operator() (BaseTimer<TTimerType> *a, BaseTimer<TTimerType> *b) const {
+			if (a->period == b->period) return a < b;
+			return a->period < b->period;
+		}
+	};
+
+	/** Singleton list, to store all the active timers. */
+	static std::set<BaseTimer<TTimerType> *, base_timer_sorter> &GetTimers() {
+		static std::set<BaseTimer<TTimerType> *, base_timer_sorter> timers;
+		return timers;
+	}
+};
+
+#endif /* TIMER_MANAGER_H */