migrate from boost::asio to the MPD EventLoop

Two years ago, ncmpc 0.32 (commit 74cc24b) made the switch from
GLib's GMainLoop to boost::asio, because that appeared to be a decent
non-blocking I/O event loop for C++, but it turned out that the API
was complicated to use, broke all the time and the generated code was
heavily bloated.

Even though importing more than 7000 lines of code from MPD sounds
like replacing one kind of bloat with another, this reduces ncmpc's
executable size from 380 kB to 240 kB (37% smaller).  The "mini" build
is reduced from 149 kB to 79 kB (47% smaller).

Closes #73

NEWS

@@ -1,4 +1,5 @@
 ncmpc 0.41 - not yet released
+* new main loop (copying code from MPD, replacing boost::asio)
 * lyrics: remove the "lyricwiki" plugin because the site is gone
 
 ncmpc 0.40 - (2020-10-07)

meson.build

@@ -326,7 +326,6 @@ ncmpc = executable('ncmpc',
   'src/Command.cxx',
   'src/Bindings.cxx',
   'src/GlobalBindings.cxx',
-  'src/UserInput.cxx',
   'src/AsyncUserInput.cxx',
   'src/KeyName.cxx',
   'src/Match.cxx',

src/AsyncUserInput.cxx

@@ -40,18 +40,11 @@ translate_key(int key)
 }
 
 void
-AsyncUserInput::OnReadable(const boost::system::error_code &error)
+AsyncUserInput::OnSocketReady(unsigned) noexcept
 {
-	if (error) {
-		get_io_context().stop();
-		return;
-	}
-
 	int key = wgetch(&w);
-	if (ignore_key(key)) {
-		AsyncWait();
+	if (ignore_key(key))
 		return;
-	}
 
 #ifdef HAVE_GETMOUSE
 	if (key == KEY_MOUSE) {
@@ -68,39 +61,38 @@ AsyncUserInput::OnReadable(const boost::system::error_code &error)
 		do_mouse_event({event.x, event.y}, event.bstate);
 		end_input_event();
 
-		AsyncWait();
 		return;
 	}
 #endif
 
 	Command cmd = translate_key(key);
-	if (cmd == Command::NONE) {
-		AsyncWait();
+	if (cmd == Command::NONE)
 		return;
-	}
 
 	begin_input_event();
 
-	if (!do_input_event(get_io_context(), cmd))
+	if (!do_input_event(socket_event.GetEventLoop(), cmd))
 		return;
 
 	end_input_event();
-	AsyncWait();
+	return;
 }
 
-AsyncUserInput::AsyncUserInput(boost::asio::io_service &io_service, WINDOW &_w)
-	:UserInput(io_service), w(_w)
+AsyncUserInput::AsyncUserInput(EventLoop &event_loop, WINDOW &_w) noexcept
+	:socket_event(event_loop, BIND_THIS_METHOD(OnSocketReady),
+		      SocketDescriptor(STDIN_FILENO)),
+	 w(_w)
 {
-	AsyncWait();
+	socket_event.ScheduleRead();
 }
 
 void
-keyboard_unread(boost::asio::io_service &io_service, int key)
+keyboard_unread(EventLoop &event_loop, int key)
 {
 	if (ignore_key(key))
 		return;
 
 	Command cmd = translate_key(key);
 	if (cmd != Command::NONE)
-		do_input_event(io_service, cmd);
+		do_input_event(event_loop, cmd);
 }

src/AsyncUserInput.hxx

@@ -20,26 +20,23 @@
 #ifndef ASYNC_USER_INPUT_HXX
 #define ASYNC_USER_INPUT_HXX
 
-#include "UserInput.hxx"
+#include "event/SocketEvent.hxx"
 
 #include <curses.h>
 
-class AsyncUserInput : public UserInput {
+class AsyncUserInput {
+	SocketEvent socket_event;
+
 	WINDOW &w;
 
 public:
-	AsyncUserInput(boost::asio::io_service &io_service, WINDOW &_w);
+	AsyncUserInput(EventLoop &event_loop, WINDOW &_w) noexcept;
 
 private:
-	void AsyncWait() {
-		UserInput::AsyncWait(std::bind(&AsyncUserInput::OnReadable, this,
-					       std::placeholders::_1));
-	}
-
-	void OnReadable(const boost::system::error_code &error);
+	void OnSocketReady(unsigned flags) noexcept;
 };
 
 void
-keyboard_unread(boost::asio::io_service &io_service, int key);
+keyboard_unread(EventLoop &event_loop, int key);
 
 #endif

src/DelayedSeek.cxx

@@ -42,25 +42,19 @@ DelayedSeek::Commit() noexcept
 void
 DelayedSeek::Cancel() noexcept
 {
-	commit_timer.cancel();
+	commit_timer.Cancel();
 }
 
 void
-DelayedSeek::OnTimer(const boost::system::error_code &error) noexcept
+DelayedSeek::OnTimer() noexcept
 {
-	if (error)
-		return;
-
 	Commit();
 }
 
 void
 DelayedSeek::ScheduleTimer() noexcept
 {
-	boost::system::error_code error;
-	commit_timer.expires_from_now(std::chrono::milliseconds(500), error);
-	commit_timer.async_wait(std::bind(&DelayedSeek::OnTimer,
-					  this, std::placeholders::_1));
+	commit_timer.Schedule(std::chrono::milliseconds(500));
 }
 
 bool

src/DelayedSeek.hxx

@@ -20,9 +20,7 @@
 #ifndef NCMPC_DELAYED_SEEK_HXX
 #define NCMPC_DELAYED_SEEK_HXX
 
-#include "AsioServiceFwd.hxx"
-
-#include <boost/asio/steady_timer.hpp>
+#include "event/TimerEvent.hxx"
 
 struct mpdclient;
 
@@ -36,12 +34,12 @@ class DelayedSeek {
 	int id = -1;
 	unsigned time;
 
-	boost::asio::steady_timer commit_timer;
+	TimerEvent commit_timer;
 
 public:
-	DelayedSeek(boost::asio::io_service &io_service,
+	DelayedSeek(EventLoop &event_loop,
 		    struct mpdclient &_c) noexcept
-		:c(_c), commit_timer(io_service) {}
+		:c(_c), commit_timer(event_loop, BIND_THIS_METHOD(OnTimer)) {}
 
 	~DelayedSeek() noexcept {
 		Cancel();
@@ -61,7 +59,7 @@ public:
 	void Cancel() noexcept;
 
 private:
-	void OnTimer(const boost::system::error_code &error) noexcept;
+	void OnTimer() noexcept;
 	void ScheduleTimer() noexcept;
 };
 

src/Instance.cxx

@@ -19,6 +19,7 @@
 
 #include "Instance.hxx"
 #include "Options.hxx"
+#include "event/SignalMonitor.hxx"
 
 #include <signal.h>
 
@@ -44,36 +45,32 @@ static constexpr TagMask global_tag_whitelist{
 #endif
 
 Instance::Instance()
-	:io_service(),
-#ifndef _WIN32
-	 sigterm(io_service, SIGTERM, SIGINT, SIGHUP),
-	 sigwinch(io_service, SIGWINCH, SIGCONT),
-#endif
-	 client(io_service,
+	:client(event_loop,
 		options.host.empty() ? nullptr : options.host.c_str(),
 		options.port,
 		options.timeout_ms,
 		options.password.empty() ? nullptr : options.password.c_str()),
-	 seek(io_service, client),
-	 reconnect_timer(io_service),
-	 update_timer(io_service),
+	 seek(event_loop, client),
+	 reconnect_timer(event_loop, BIND_THIS_METHOD(OnReconnectTimer)),
+	 update_timer(event_loop, BIND_THIS_METHOD(OnUpdateTimer)),
 #ifndef NCMPC_MINI
-	 check_key_bindings_timer(io_service),
+	 check_key_bindings_timer(event_loop, BIND_THIS_METHOD(OnCheckKeyBindings)),
 #endif
-	 screen_manager(io_service),
+	 screen_manager(event_loop),
 #ifdef ENABLE_LIRC
-	 lirc_input(io_service),
+	 lirc_input(event_loop),
 #endif
-	 user_input(io_service, *screen_manager.main_window.w)
+	 user_input(event_loop, *screen_manager.main_window.w)
 {
 	screen_manager.Init(&client);
 
-	sigterm.async_wait([this](const auto &, int){
-			this->io_service.stop();
-		});
-
 #ifndef _WIN32
-	AsyncWaitSigwinch();
+	SignalMonitorInit(event_loop);
+	SignalMonitorRegister(SIGTERM, BIND_THIS_METHOD(Quit));
+	SignalMonitorRegister(SIGINT, BIND_THIS_METHOD(Quit));
+	SignalMonitorRegister(SIGHUP, BIND_THIS_METHOD(Quit));
+	SignalMonitorRegister(SIGWINCH, BIND_THIS_METHOD(OnSigwinch));
+	SignalMonitorRegister(SIGCONT, BIND_THIS_METHOD(OnSigwinch));
 #endif
 
 #ifdef HAVE_TAG_WHITELIST
@@ -92,12 +89,13 @@ Instance::Instance()
 Instance::~Instance()
 {
 	screen_manager.Exit();
+	SignalMonitorFinish();
 }
 
 void
 Instance::Run()
 {
 	screen_manager.Update(client, seek);
 
-	io_service.run();
+	event_loop.Run();
 }