store-worker: implement

store-worker is a thread + async queue to throttle requests to a single thread.

lib/mu-store-worker.cc

@@ -0,0 +1,68 @@
+/*
+** Copyright (C) 2024 Dirk-Jan C. Binnema <djcb@djcbsoftware.nl>
+**
+** 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 3, 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; if not, write to the Free Software Foundation,
+** Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+**
+*/
+
+#include "mu-store-worker.hh"
+#include "mu-store.hh"
+#include "utils/mu-utils.hh"
+
+#include <type_traits>
+
+using namespace Mu;
+
+// helper constant for the visitor
+template<class> inline constexpr bool always_false_v = false;
+
+void
+StoreWorker::run() {
+
+	running_ = true;
+
+	while (running_) {
+		WorkItem workitem;
+
+		if (!q_.pop(workitem))
+			continue;
+
+		std::visit([&](auto&& item) {
+			using T = std::decay_t<decltype(item)>;
+
+			if constexpr (std::is_same_v<T, SexpCommand>) {
+				if (!sexp_handler_)
+					mu_critical("no handler for sexp '{}'", item);
+				else
+					sexp_handler_(item);
+			} else if constexpr (std::is_same_v<T, SetDirStamp>) {
+				store_.set_dirstamp(item.path, item.tstamp);
+			} else if constexpr (std::is_same_v<T, SetLastIndex>) {
+				store_.config().set<Mu::Config::Id::LastIndex>(item.tstamp);
+			} else if constexpr (std::is_same_v<T, StartTransaction>) {
+				store_.xapian_db().request_transaction();
+			} else if constexpr (std::is_same_v<T, EndTransaction>) {
+				store_.xapian_db().request_commit(true);
+			} else if constexpr (std::is_same_v<T, RemoveMessages>) {
+				store_.remove_messages(item);
+			} else if constexpr (std::is_same_v<T, AddMessage>) {
+				store_.consume_message(std::move(item.msg), true/*new*/);
+			} else if constexpr (std::is_same_v<T, UpdateMessage>) {
+				store_.consume_message(std::move(item.msg), false/*maybe not new*/);
+			} else
+				static_assert(always_false_v<T>, "non-exhaustive visitor");
+		}, workitem);
+	}
+}