client/BackgroundCommand: infrastructure for commands running in background

src/client/ThreadBackgroundCommand.cxx

@@ -0,0 +1,76 @@
+/*
+ * Copyright 2003-2019 The Music Player Daemon Project
+ * http://www.musicpd.org
+ *
+ * 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; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#include "ThreadBackgroundCommand.hxx"
+#include "Client.hxx"
+#include "Response.hxx"
+#include "command/CommandError.hxx"
+#include "protocol/Result.hxx"
+
+ThreadBackgroundCommand::ThreadBackgroundCommand(Client &_client) noexcept
+	:thread(BIND_THIS_METHOD(_Run)),
+	 defer_finish(_client.GetEventLoop(), BIND_THIS_METHOD(DeferredFinish)),
+	 client(_client)
+{
+}
+
+void
+ThreadBackgroundCommand::_Run() noexcept
+{
+	assert(!error);
+
+	try {
+		Run();
+	} catch (...) {
+		error = std::current_exception();
+	}
+
+	defer_finish.Schedule();
+}
+
+void
+ThreadBackgroundCommand::DeferredFinish() noexcept
+{
+	/* free the Thread */
+	thread.Join();
+
+	/* send the response */
+	Response response(client, 0);
+
+	if (!error) {
+		PrintError(response, std::move(error));
+	} else {
+		SendResponse(response);
+		command_success(client);
+	}
+
+	/* delete this object */
+	client.OnBackgroundCommandFinished();
+}
+
+void
+ThreadBackgroundCommand::Cancel() noexcept
+{
+	CancelThread();
+	thread.Join();
+
+	/* cancel the DeferEvent, just in case the Thread has
+	   meanwhile finished execution */
+	defer_finish.Cancel();
+}