lib/dbus/AsyncRequest: new helper class

Makefile.am

@@ -285,6 +285,7 @@ if ENABLE_DBUS
 noinst_LIBRARIES += libodbus.a
 libodbus_a_SOURCES = \
 	src/lib/dbus/AppendIter.hxx \
+	src/lib/dbus/AsyncRequest.hxx \
 	src/lib/dbus/Connection.cxx src/lib/dbus/Connection.hxx \
 	src/lib/dbus/Error.cxx src/lib/dbus/Error.hxx \
 	src/lib/dbus/Iter.hxx \

src/lib/dbus/AsyncRequest.hxx

+/*
+ * 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

src/neighbor/plugins/UdisksNeighborPlugin.cxx

@@ -23,7 +23,7 @@
 #include "lib/dbus/Error.hxx"
 #include "lib/dbus/Glue.hxx"
 #include "lib/dbus/Message.hxx"
-#include "lib/dbus/PendingCall.hxx"
+#include "lib/dbus/AsyncRequest.hxx"
 #include "lib/dbus/ReadIter.hxx"
 #include "lib/dbus/ObjectManager.hxx"
 #include "lib/dbus/UDisks2.hxx"
@@ -82,7 +82,7 @@ class UdisksNeighborExplorer final
 
 	Manual<SafeSingleton<ODBus::Glue>> dbus_glue;
 
-	ODBus::PendingCall pending_list_call;
+	ODBus::AsyncRequest list_request;
 
 	/**
 	 * Protects #by_uri, #by_path.
@@ -118,13 +118,7 @@ private:
 	void Insert(UdisksObject &&o) noexcept;
 	void Remove(const std::string &path) noexcept;
 
-	void OnListNotify(DBusPendingCall *pending) noexcept;
-
-	static void OnListNotify(DBusPendingCall *pending,
-				 void *user_data) noexcept {
-		auto &e = *(UdisksNeighborExplorer *)user_data;
-		e.OnListNotify(pending);
-	}
+	void OnListNotify(ODBus::Message reply) noexcept;
 
 	DBusHandlerResult HandleMessage(DBusConnection *dbus_connection,
 					DBusMessage *message) noexcept;
@@ -159,8 +153,9 @@ UdisksNeighborExplorer::DoOpen()
 						  UDISKS2_PATH,
 						  DBUS_OM_INTERFACE,
 						  "GetManagedObjects");
-		pending_list_call = PendingCall::SendWithReply(connection, msg.Get());
-		pending_list_call.SetNotify(OnListNotify, this);
+		list_request.Send(connection, *msg.Get(),
+				  std::bind(&UdisksNeighborExplorer::OnListNotify,
+					    this, std::placeholders::_1));
 	} catch (...) {
 		dbus_glue.Destruct();
 		throw;
@@ -176,8 +171,8 @@ UdisksNeighborExplorer::Open()
 inline void
 UdisksNeighborExplorer::DoClose() noexcept
 {
-	if (pending_list_call) {
-		pending_list_call.Cancel();
+	if (list_request) {
+		list_request.Cancel();
 	}
 
 	// TODO: remove_match
@@ -317,14 +312,9 @@ UdisksNeighborExplorer::Remove(const std::string &path) noexcept
 }
 
 inline void
-UdisksNeighborExplorer::OnListNotify(DBusPendingCall *pending) noexcept
+UdisksNeighborExplorer::OnListNotify(ODBus::Message reply) noexcept
 {
-	assert(pending == pending_list_call.Get());
-
-	pending_list_call = {};
-
 	using namespace ODBus;
-	Message reply = Message::StealReply(*pending);
 
 	try {
 		reply.CheckThrowError();