WIP, first working genetic algorithm to train the neural network

src/database/SessionPool.cpp

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+/*
+ * Copyright (C) 2019 Emeric Poupon
+ *
+ * This file is part of LMS.
+ *
+ * LMS 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 3 of the License, or
+ * (at your option) any later version.
+ *
+ * LMS 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 LMS.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "SessionPool.hpp"
+
+#include "utils/Exception.hpp"
+#include "utils/Logger.hpp"
+
+#include "Session.hpp"
+
+namespace Database {
+
+SessionPool::SessionPool(Db& database, std::size_t maxSessionCount)
+: _db {database},
+_maxSessionCount {maxSessionCount}
+{
+}
+
+Session&
+SessionPool::acquireSession()
+{
+	std::scoped_lock lock {_mutex};
+
+	if (_freeSessions.empty())
+	{
+		if (_acquiredSessions.size() == _maxSessionCount)
+			throw LmsException {"Too many database sessions!"};
+
+		_freeSessions.emplace_back(std::make_unique<Session>(_db));
+	}
+
+	std::unique_ptr<Session> session {std::move(_freeSessions.back())};
+	_freeSessions.pop_back();
+	_acquiredSessions.push_back(std::move(session));
+
+	return *_acquiredSessions.back().get();
+}
+
+void
+SessionPool::releaseSession(Session& sessionToRelease)
+{
+	std::scoped_lock lock {_mutex};
+
+	auto it {std::find_if(std::begin(_acquiredSessions), std::end(_acquiredSessions), [&](const std::unique_ptr<Session>& session) { return session.get() == &sessionToRelease; })};
+	if (it == std::end(_acquiredSessions))
+		throw LmsException {"Unknown released Session!"};
+
+	std::unique_ptr<Session> session {std::move(*it)};
+	_acquiredSessions.erase(it);
+	_freeSessions.push_back(std::move(session));
+}
+
+} // namespace Database