lib/dbus/AsyncRequest: new helper class

src/lib/dbus/AsyncRequest.hxx

@@ -0,0 +1,111 @@
+/*
+ * Copyright (C) 2018 Max Kellermann <max.kellermann@gmail.com>
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *
+ * - Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the
+ * distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE
+ * FOUNDATION OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
+ * OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#ifndef ODBUS_ASYNC_REQUEST_HXX
+#define ODBUS_ASYNC_REQUEST_HXX
+
+#include "PendingCall.hxx"
+
+#include <functional>
+
+#include <assert.h>
+
+namespace ODBus {
+
+class Message;
+
+/**
+ * Helper class which makes sending messages and receiving the
+ * response asynchronously easy.
+ *
+ * Remember to always cancel pending operations before destructing
+ * this class.
+ */
+class AsyncRequest {
+	PendingCall pending_call;
+
+	std::function<void(Message) noexcept> callback;
+
+public:
+	operator bool() const noexcept {
+		return pending_call;
+	}
+
+	/**
+	 * Send a message on the specified connection and invoke the
+	 * given callback upon completion (or error).
+	 *
+	 * The callback should invoke Message::CheckThrowError() to
+	 * check for errors.
+	 *
+	 * This object must be kept around until the operation
+	 * completes.  It can only be reused after completion.
+	 */
+	template<typename F>
+	void Send(DBusConnection &connection,
+		  DBusMessage &message,
+		  int timeout_milliseconds,
+		  F &&_callback) {
+		assert(!pending_call);
+
+		callback = std::forward<F>(_callback);
+		pending_call = PendingCall::SendWithReply(&connection,
+							  &message,
+							  timeout_milliseconds);
+		pending_call.SetNotify(Notify, this);
+	}
+
+	template<typename F>
+	void Send(DBusConnection &connection,
+		  DBusMessage &message,
+		  F &&_callback) {
+		Send(connection, message, -1, std::forward<F>(_callback));
+	}
+
+	void Cancel() {
+		pending_call.Cancel();
+	}
+
+private:
+	void Notify(DBusPendingCall *pending) noexcept {
+		assert(pending_call.Get() == pending);
+		pending_call = {};
+		std::exchange(callback, {})(Message::StealReply(*pending));
+	}
+
+	static void Notify(DBusPendingCall *pending,
+			   void *user_data) noexcept {
+		auto &ar = *(AsyncRequest *)user_data;
+		ar.Notify(pending);
+	}
+};
+
+} /* namespace ODBus */
+
+#endif