event/Loop: manage all SocketEvents in a linked list

src/event/Loop.cxx

@@ -67,6 +67,8 @@ EventLoop::~EventLoop() noexcept
 {
 	assert(idle.empty());
 	assert(timers.empty());
+	assert(sockets.empty());
+	assert(ready_sockets.empty());
 }
 
 #ifdef HAVE_URING
@@ -117,7 +119,11 @@ EventLoop::AddFD(int fd, unsigned events, SocketEvent &event) noexcept
 	assert(!IsAlive() || IsInside());
 #endif
 
-	return poll_group.Add(fd, events, &event);
+	if (!poll_group.Add(fd, events, &event))
+		return false;
+
+	sockets.push_back(event);
+	return true;
 }
 
 bool
@@ -131,12 +137,13 @@ EventLoop::ModifyFD(int fd, unsigned events, SocketEvent &event) noexcept
 }
 
 bool
-EventLoop::RemoveFD(int fd) noexcept
+EventLoop::RemoveFD(int fd, SocketEvent &event) noexcept
 {
 #ifdef HAVE_THREADED_EVENT_LOOP
 	assert(!IsAlive() || IsInside());
 #endif
 
+	event.unlink();
 	return poll_group.Remove(fd);
 }
 
@@ -213,11 +220,13 @@ EventLoop::Wait(Event::Duration timeout) noexcept
 	const auto poll_result =
 		poll_group.ReadEvents(ExportTimeoutMS(timeout));
 
-	ready_sockets.clear();
 	for (size_t i = 0; i < poll_result.GetSize(); ++i) {
-		auto &s = *(SocketEvent *)poll_result.GetObject(i);
-		s.SetReadyFlags(poll_result.GetEvents(i));
-		ready_sockets.push_back(s);
+		auto &socket_event = *(SocketEvent *)poll_result.GetObject(i);
+		socket_event.SetReadyFlags(poll_result.GetEvents(i));
+
+		/* move from "sockets" to "ready_sockets" */
+		socket_event.unlink();
+		ready_sockets.push_back(socket_event);
 	}
 
 	return poll_result.GetSize() > 0;
@@ -309,10 +318,13 @@ EventLoop::Run() noexcept
 
 		/* invoke sockets */
 		while (!ready_sockets.empty() && !quit) {
-			auto &sm = ready_sockets.front();
-			ready_sockets.pop_front();
+			auto &socket_event = ready_sockets.front();
+
+			/* move from "ready_sockets" back to "sockets" */
+			socket_event.unlink();
+			sockets.push_back(socket_event);
 
-			sm.Dispatch();
+			socket_event.Dispatch();
 		}
 	} while (!quit);
 

src/event/Loop.hxx

@@ -91,18 +91,22 @@ class EventLoop final
 	DeferredList deferred;
 #endif
 
-	using ReadySocketList =
+	using SocketList =
 		boost::intrusive::list<SocketEvent,
-				       boost::intrusive::member_hook<SocketEvent,
-								     SocketEvent::ReadyListHook,
-								     &SocketEvent::ready_siblings>,
+				       boost::intrusive::base_hook<boost::intrusive::list_base_hook<boost::intrusive::link_mode<boost::intrusive::auto_unlink>>>,
 				       boost::intrusive::constant_time_size<false>>;
 
 	/**
+	 * A list of scheduled #SocketEvent instances, without those
+	 * which are ready (these are in #ready_sockets).
+	 */
+	SocketList sockets;
+
+	/**
 	 * A linked list of #SocketEvent instances which have a
 	 * non-zero "ready_flags" field, and need to be dispatched.
 	 */
-	ReadySocketList ready_sockets;
+	SocketList ready_sockets;
 
 #ifdef HAVE_URING
 	std::unique_ptr<Uring::Manager> uring;
@@ -188,7 +192,7 @@ public:
 
 	bool AddFD(int fd, unsigned events, SocketEvent &event) noexcept;
 	bool ModifyFD(int fd, unsigned events, SocketEvent &event) noexcept;
-	bool RemoveFD(int fd) noexcept;
+	bool RemoveFD(int fd, SocketEvent &event) noexcept;
 
 	/**
 	 * Remove the given #SocketEvent after the file descriptor

src/event/SocketEvent.cxx

@@ -69,7 +69,7 @@ SocketEvent::Schedule(unsigned flags) noexcept
 	if (scheduled_flags == 0)
 		success = loop.AddFD(fd.Get(), flags, *this);
 	else if (flags == 0)
-		success = loop.RemoveFD(fd.Get());
+		success = loop.RemoveFD(fd.Get(), *this);
 	else
 		success = loop.ModifyFD(fd.Get(), flags, *this);
 

src/event/SocketEvent.hxx

@@ -45,14 +45,11 @@ class EventLoop;
  * thread that runs the #EventLoop, except where explicitly documented
  * as thread-safe.
  */
-class SocketEvent {
+class SocketEvent final : public boost::intrusive::list_base_hook<boost::intrusive::link_mode<boost::intrusive::auto_unlink>> {
 	friend class EventLoop;
 
 	EventLoop &loop;
 
-	using ReadyListHook = boost::intrusive::list_member_hook<boost::intrusive::link_mode<boost::intrusive::auto_unlink>>;
-	ReadyListHook ready_siblings;
-
 	using Callback = BoundMethod<void(unsigned events) noexcept>;
 	const Callback callback;