event/IdleEvent: make a special case of DeferEvent

src/event/DeferEvent.cxx

@@ -28,3 +28,12 @@ DeferEvent::Schedule() noexcept
 
 	assert(IsPending());
 }
+
+void
+DeferEvent::ScheduleIdle() noexcept
+{
+	if (!IsPending())
+		loop.AddIdle(*this);
+
+	assert(IsPending());
+}

src/event/DeferEvent.hxx

@@ -60,6 +60,12 @@ public:
 
 	void Schedule() noexcept;
 
+	/**
+	 * Schedule this event, but only after the #EventLoop is idle,
+	 * i.e. before going to sleep.
+	 */
+	void ScheduleIdle() noexcept;
+
 	void Cancel() noexcept {
 		if (IsPending())
 			unlink();

src/event/FullyBufferedSocket.cxx

@@ -97,7 +97,7 @@ FullyBufferedSocket::OnSocketReady(unsigned flags) noexcept
 {
 	if (flags & SocketEvent::WRITE) {
 		assert(!output.empty());
-		assert(!idle_event.IsActive());
+		assert(!idle_event.IsPending());
 
 		if (!Flush())
 			return;

src/event/IdleEvent.cxx

@@ -18,26 +18,3 @@
  */
 
 #include "IdleEvent.hxx"
-#include "Loop.hxx"
-
-#include <cassert>
-
-void
-IdleEvent::Schedule() noexcept
-{
-	assert(loop.IsInside());
-
-	if (IsActive())
-		/* already scheduled */
-		return;
-
-	loop.AddIdle(*this);
-}
-
-void
-IdleEvent::Run() noexcept
-{
-	assert(loop.IsInside());
-
-	callback();
-}

src/event/IdleEvent.hxx

@@ -20,8 +20,7 @@
 #ifndef MPD_SOCKET_IDLE_EVENT_HXX
 #define MPD_SOCKET_IDLE_EVENT_HXX
 
-#include "util/BindMethod.hxx"
-#include "util/IntrusiveList.hxx"
+#include "DeferEvent.hxx"
 
 class EventLoop;
 
@@ -33,39 +32,30 @@ class EventLoop;
  * thread that runs the #EventLoop, except where explicitly documented
  * as thread-safe.
  */
-class IdleEvent final : public AutoUnlinkIntrusiveListHook {
-	friend class EventLoop;
-	friend class IntrusiveList<IdleEvent>;
-
-	EventLoop &loop;
+class IdleEvent final {
+	DeferEvent event;
 
 	using Callback = BoundMethod<void() noexcept>;
-	const Callback callback;
 
 public:
 	IdleEvent(EventLoop &_loop, Callback _callback) noexcept
-		:loop(_loop), callback(_callback) {}
-
-	IdleEvent(const IdleEvent &) = delete;
-	IdleEvent &operator=(const IdleEvent &) = delete;
+		:event(_loop, _callback) {}
 
 	auto &GetEventLoop() const noexcept {
-		return loop;
+		return event.GetEventLoop();
 	}
 
-	bool IsActive() const noexcept {
-		return is_linked();
+	bool IsPending() const noexcept {
+		return event.IsPending();
 	}
 
-	void Schedule() noexcept;
+	void Schedule() noexcept {
+		event.ScheduleIdle();
+	}
 
 	void Cancel() noexcept {
-		if (IsActive())
-			unlink();
+		event.Cancel();
 	}
-
-private:
-	void Run() noexcept;
 };
 
 #endif

src/event/Loop.cxx

@@ -154,15 +154,6 @@ EventLoop::RemoveFD(int fd, SocketEvent &event) noexcept
 }
 
 void
-EventLoop::AddIdle(IdleEvent &i) noexcept
-{
-	assert(IsInside());
-
-	idle.push_back(i);
-	again = true;
-}
-
-void
 EventLoop::AddTimer(TimerEvent &t, Event::Duration d) noexcept
 {
 	assert(IsInside());
@@ -203,6 +194,13 @@ EventLoop::AddDeferred(DeferEvent &d) noexcept
 }
 
 void
+EventLoop::AddIdle(DeferEvent &e) noexcept
+{
+	idle.push_front(e);
+	again = true;
+}
+
+void
 EventLoop::RunDeferred() noexcept
 {
 	while (!defer.empty() && !quit) {
@@ -212,6 +210,19 @@ EventLoop::RunDeferred() noexcept
 	}
 }
 
+bool
+EventLoop::RunOneIdle() noexcept
+{
+	if (idle.empty())
+		return false;
+
+	idle.pop_front_and_dispose([](DeferEvent *e){
+		e->Run();
+	});
+
+	return true;
+}
+
 template<class ToDuration, class Rep, class Period>
 static constexpr ToDuration
 duration_cast_round_up(std::chrono::duration<Rep, Period> d) noexcept
@@ -301,16 +312,12 @@ EventLoop::Run() noexcept
 
 		RunDeferred();
 
-		/* invoke idle */
-
-		while (!idle.empty()) {
-			IdleEvent &m = idle.front();
-			idle.pop_front();
-			m.Run();
-
-			if (quit)
-				return;
-		}
+		if (RunOneIdle())
+			/* check for other new events after each
+			   "idle" invocation to ensure that the other
+			   "idle" events are really invoked at the
+			   very end */
+			continue;
 
 #ifdef HAVE_THREADED_EVENT_LOOP
 		/* try to handle DeferEvents without WakeFD

src/event/Loop.hxx

@@ -47,7 +47,6 @@ namespace Uring { class Queue; class Manager; }
 #endif
 
 class TimerEvent;
-class IdleEvent;
 class DeferEvent;
 class InjectEvent;
 
@@ -58,7 +57,7 @@ class InjectEvent;
  * thread that runs it, except where explicitly documented as
  * thread-safe.
  *
- * @see SocketEvent, MultiSocketMonitor, TimerEvent, IdleEvent
+ * @see SocketEvent, MultiSocketMonitor, TimerEvent, DeferEvent, InjectEvent
  */
 class EventLoop final
 {
@@ -83,8 +82,10 @@ class EventLoop final
 
 	DeferList defer;
 
-	using IdleList = IntrusiveList<IdleEvent>;
-	IdleList idle;
+	/**
+	 * This is like #defer, but gets invoked when the loop is idle.
+	 */
+	DeferList idle;
 
 #ifdef HAVE_THREADED_EVENT_LOOP
 	Mutex mutex;
@@ -203,14 +204,13 @@ public:
 	 */
 	bool AbandonFD(SocketEvent &event) noexcept;
 
-	void AddIdle(IdleEvent &i) noexcept;
-
 	void AddTimer(TimerEvent &t, Event::Duration d) noexcept;
 
 	/**
 	 * Schedule a call to DeferEvent::RunDeferred().
 	 */
 	void AddDeferred(DeferEvent &d) noexcept;
+	void AddIdle(DeferEvent &e) noexcept;
 
 #ifdef HAVE_THREADED_EVENT_LOOP
 	/**
@@ -238,6 +238,13 @@ public:
 private:
 	void RunDeferred() noexcept;
 
+	/**
+	 * Invoke one "idle" #DeferEvent.
+	 *
+	 * @return false if there was no such event
+	 */
+	bool RunOneIdle() noexcept;
+
 #ifdef HAVE_THREADED_EVENT_LOOP
 	/**
 	 * Invoke all pending InjectEvents.