Safer implementation of signal handlers in ncurses.cc

On recent ncurses implementation on cygwin, the old method provoked
freezes. Avoid calling ncurses functions in signal handlers.

We still call an unsafe function (EventManager::force_signal)...

src/ncurses.cc

@@ -140,15 +140,19 @@ static void set_color(WINDOW* window, ColorPair colors)
     }
 }
 
+static sig_atomic_t resize_pending = 0;
+
 void on_term_resize(int)
 {
-    ungetch(KEY_RESIZE);
+    resize_pending = 1;
     EventManager::instance().force_signal(0);
 }
 
+static sig_atomic_t ctrl_c_pending = 0;
+
 void on_sigint(int)
 {
-    ungetch(CTRL('c'));
+    ctrl_c_pending = 1;
     EventManager::instance().force_signal(0);
 }
 
@@ -267,6 +271,8 @@ void NCursesUI::draw(const DisplayBuffer& display_buffer,
                      const DisplayLine& status_line,
                      const DisplayLine& mode_line)
 {
+    check_resize();
+
     LineCount line_index = 0;
     for (const DisplayLine& line : display_buffer.lines())
     {
@@ -315,8 +321,29 @@ void NCursesUI::draw(const DisplayBuffer& display_buffer,
     m_dirty = true;
 }
 
+void NCursesUI::check_resize()
+{
+    if (resize_pending)
+    {
+        int fd = open("/dev/tty", O_RDWR);
+        winsize ws;
+        if (ioctl(fd, TIOCGWINSZ, (void*)&ws) == 0)
+        {
+            close(fd);
+            resizeterm(ws.ws_row, ws.ws_col);
+            update_dimensions();
+        }
+        resize_pending = false;
+    }
+}
+
 bool NCursesUI::is_key_available()
 {
+    check_resize();
+
+    if (ctrl_c_pending)
+        return true;
+
     timeout(0);
     const int c = getch();
     if (c != ERR)
@@ -327,6 +354,14 @@ bool NCursesUI::is_key_available()
 
 Key NCursesUI::get_key()
 {
+    check_resize();
+
+    if (ctrl_c_pending)
+    {
+        ctrl_c_pending = false;
+        return ctrl('c');
+    }
+
     const int c = getch();
     if (c > 0 and c < 27)
     {
@@ -344,18 +379,6 @@ Key NCursesUI::get_key()
         else
             return Key::Escape;
     }
-    else if (c == KEY_RESIZE)
-    {
-        int fd = open("/dev/tty", O_RDWR);
-        winsize ws;
-        if (fd != -1 and ioctl(fd, TIOCGWINSZ, (void*)&ws) == 0)
-        {
-            close(fd);
-            resizeterm(ws.ws_row, ws.ws_col);
-            update_dimensions();
-        }
-        return Key::Invalid;
-    }
     else switch (c)
     {
     case KEY_BACKSPACE: case 127: return Key::Backspace;

src/ncurses.hh

@@ -45,7 +45,7 @@ public:
 
     static void abort();
 private:
-    friend void on_term_resize(int);
+    void check_resize();
     void redraw();
     void draw_line(const DisplayLine& line, CharCount col_index) const;