Do not select on non-urgent fd when handling only urgent events

This avoids 100% CPU usage when we have pending fifo input while running
a shell process, as we will not end-up busy looping in pselect but not
reading the available data due to being only processing urgent events.

src/buffer_utils.cc

@@ -133,7 +133,7 @@ Buffer* create_fifo_buffer(String name, int fd, Buffer::Flags flags, bool scroll
     struct FifoWatcher : FDWatcher
     {
         FifoWatcher(int fd, Buffer& buffer, bool scroll)
-            : FDWatcher(fd, FdEvents::Read,
+            : FDWatcher(fd, FdEvents::Read, EventMode::Normal,
                         [](FDWatcher& watcher, FdEvents, EventMode mode) {
                             if (mode == EventMode::Normal)
                                 static_cast<FifoWatcher&>(watcher).read_fifo();

src/event_manager.cc

@@ -12,8 +12,8 @@
 namespace Kakoune
 {
 
-FDWatcher::FDWatcher(int fd, FdEvents events, Callback callback)
-    : m_fd{fd}, m_events{events}, m_callback{std::move(callback)}
+FDWatcher::FDWatcher(int fd, FdEvents events, EventMode mode, Callback callback)
+    : m_fd{fd}, m_events{events}, m_mode{mode}, m_callback{std::move(callback)}
 {
     EventManager::instance().m_fd_watchers.push_back(this);
 }
@@ -80,6 +80,9 @@ bool EventManager::handle_next_events(EventMode mode, sigset_t* sigmask, bool bl
     FD_ZERO(&rfds); FD_ZERO(&wfds); FD_ZERO(&efds);
     for (auto& watcher : m_fd_watchers)
     {
+        if (watcher->mode() == EventMode::Normal and mode == EventMode::Urgent)
+            continue;
+
         const int fd = watcher->fd();
         if (fd != -1)
         {

src/event_manager.hh

@@ -34,7 +34,7 @@ class FDWatcher
 {
 public:
     using Callback = std::function<void (FDWatcher& watcher, FdEvents events, EventMode mode)>;
-    FDWatcher(int fd, FdEvents events, Callback callback);
+    FDWatcher(int fd, FdEvents events, EventMode mode, Callback callback);
     FDWatcher(const FDWatcher&) = delete;
     FDWatcher& operator=(const FDWatcher&) = delete;
     ~FDWatcher();
@@ -42,6 +42,7 @@ public:
     int fd() const { return m_fd; }
     FdEvents events() const { return m_events; }
     FdEvents& events() { return m_events; }
+    EventMode mode() const { return m_mode; }
 
     void run(FdEvents events, EventMode mode);
 
@@ -51,6 +52,7 @@ public:
 private:
     int      m_fd;
     FdEvents m_events;
+    EventMode m_mode;
     Callback m_callback;
 };
 

src/json_ui.cc

@@ -133,7 +133,7 @@ void rpc_call(StringView method, Args&&... args)
 }
 
 JsonUI::JsonUI()
-    : m_stdin_watcher{0, FdEvents::Read,
+    : m_stdin_watcher{0, FdEvents::Read, EventMode::Urgent,
                       [this](FDWatcher&, FdEvents, EventMode mode) {
         parse_requests(mode);
       }}, m_dimensions{24, 80}

src/ncurses_ui.cc

@@ -327,7 +327,7 @@ static void signal_handler(int)
 
 NCursesUI::NCursesUI()
     : m_cursor{CursorMode::Buffer, {}},
-      m_stdin_watcher{STDIN_FILENO, FdEvents::Read,
+      m_stdin_watcher{STDIN_FILENO, FdEvents::Read, EventMode::Urgent,
                       [this](FDWatcher&, FdEvents, EventMode) {
         if (not m_on_key)
             return;

src/remote.cc

@@ -461,7 +461,7 @@ static bool send_data(int fd, RemoteBuffer& buffer, Optional<int> ancillary_fd =
 }
 
 RemoteUI::RemoteUI(int socket, DisplayCoord dimensions)
-    : m_socket_watcher(socket,  FdEvents::Read | FdEvents::Write,
+    : m_socket_watcher(socket,  FdEvents::Read | FdEvents::Write, EventMode::Urgent,
                        [this](FDWatcher& watcher, FdEvents events, EventMode) {
           const int sock = watcher.fd();
           try
@@ -663,7 +663,7 @@ RemoteClient::RemoteClient(StringView session, StringView name, std::unique_ptr<
         m_socket_watcher->events() |= FdEvents::Write;
      });
 
-    m_socket_watcher.reset(new FDWatcher{sock, FdEvents::Read | FdEvents::Write,
+    m_socket_watcher.reset(new FDWatcher{sock, FdEvents::Read | FdEvents::Write, EventMode::Urgent,
                            [this, reader = MsgReader{}](FDWatcher& watcher, FdEvents events, EventMode) mutable {
         const int sock = watcher.fd();
         if (events & FdEvents::Write and send_data(sock, m_send_buffer))
@@ -777,7 +777,7 @@ class Server::Accepter
 {
 public:
     Accepter(int socket)
-        : m_socket_watcher(socket, FdEvents::Read,
+        : m_socket_watcher(socket, FdEvents::Read, EventMode::Urgent,
                            [this](FDWatcher&, FdEvents, EventMode mode) {
                                handle_available_input(mode);
                            })
@@ -888,7 +888,7 @@ Server::Server(String session_name, bool is_daemon)
 
         m_accepters.emplace_back(new Accepter{sock});
     };
-    m_listener.reset(new FDWatcher{listen_sock, FdEvents::Read, accepter});
+    m_listener.reset(new FDWatcher{listen_sock, FdEvents::Read, EventMode::Urgent, accepter});
 }
 
 bool Server::rename_session(StringView name)

src/shell_manager.cc

@@ -167,7 +167,7 @@ Vector<String> generate_env(StringView cmdline, const Context& context, const Sh
 
 FDWatcher make_pipe_reader(Pipe& pipe, String& contents)
 {
-    return {pipe.read_fd(), FdEvents::Read,
+    return {pipe.read_fd(), FdEvents::Read, EventMode::Urgent,
             [&contents, &pipe](FDWatcher& watcher, FdEvents, EventMode) {
         char buffer[1024];
         while (fd_readable(pipe.read_fd()))
@@ -188,7 +188,7 @@ FDWatcher make_pipe_writer(Pipe& pipe, StringView contents)
 {
     int flags = fcntl(pipe.write_fd(), F_GETFL, 0);
     fcntl(pipe.write_fd(), F_SETFL, flags | O_NONBLOCK);
-    return {pipe.write_fd(), FdEvents::Write,
+    return {pipe.write_fd(), FdEvents::Write, EventMode::Urgent,
             [contents, &pipe](FDWatcher& watcher, FdEvents, EventMode) mutable {
         while (fd_writable(pipe.write_fd()))
         {