Improve UNIX signal handling (#518)

There was a dead lock caused by the reentrancy of the post method.

Co-authored-by: ArthurSonzogni <sonzogniarthur@gmail.com>

include/ftxui/component/screen_interactive.hpp

@@ -52,6 +52,8 @@ class ScreenInteractive : public Screen {
   Closure WithRestoredIO(Closure);
 
  private:
+  void ExitNow();
+
   void Install();
   void Uninstall();
 
@@ -64,8 +66,9 @@ class ScreenInteractive : public Screen {
 
   void HandleTask(Component component, Task& task);
   void Draw(Component component);
+  void ResetCursorPosition();
 
-  void SigStop();
+  void Signal(int signal);
 
   ScreenInteractive* suspended_screen_ = nullptr;
   enum class Dimension {
@@ -106,7 +109,7 @@ class ScreenInteractive : public Screen {
  public:
   class Private {
    public:
-    static void SigStop(ScreenInteractive& s) { return s.SigStop(); }
+    static void Signal(ScreenInteractive& s, int signal) { s.Signal(signal); }
   };
   friend Private;
 };

src/ftxui/component/screen_interactive.cpp

@@ -148,7 +148,8 @@ void ftxui_on_resize(int columns, int rows) {
 }
 }
 
-#else
+#else  // POSIX (Linux & Mac)
+
 #include <sys/time.h>  // for timeval
 
 int CheckStdinReady(int usec_timeout) {
@@ -178,9 +179,74 @@ void EventListener(std::atomic<bool>* quit, Sender<Task> out) {
     }
   }
 }
-
 #endif
 
+std::stack<Closure> on_exit_functions;  // NOLINT
+void OnExit() {
+  while (!on_exit_functions.empty()) {
+    on_exit_functions.top()();
+    on_exit_functions.pop();
+  }
+}
+
+std::atomic<int> g_signal_exit_count = 0;
+#if !defined(_WIN32)
+std::atomic<int> g_signal_stop_count = 0;
+std::atomic<int> g_signal_resize_count = 0;
+#endif
+
+// Async signal safe function
+void RecordSignal(int signal) {
+  switch (signal) {
+    case SIGABRT:
+    case SIGFPE:
+    case SIGILL:
+    case SIGINT:
+    case SIGSEGV:
+    case SIGTERM:
+      g_signal_exit_count++;
+      break;
+
+#if !defined(_WIN32)
+    case SIGTSTP:
+      g_signal_stop_count++;
+      break;
+
+    case SIGWINCH:
+      g_signal_resize_count++;
+      break;
+#endif
+
+    default:
+      break;
+  }
+}
+
+void ExecuteSignalHandlers() {
+  int signal_exit_count = g_signal_exit_count.exchange(0);
+  while (signal_exit_count--) {
+    ScreenInteractive::Private::Signal(*g_active_screen, SIGABRT);
+  }
+
+#if !defined(_WIN32)
+  int signal_stop_count = g_signal_stop_count.exchange(0);
+  while (signal_stop_count--) {
+    ScreenInteractive::Private::Signal(*g_active_screen, SIGTSTP);
+  }
+
+  int signal_resize_count = g_signal_resize_count.exchange(0);
+  while (signal_resize_count--) {
+    ScreenInteractive::Private::Signal(*g_active_screen, SIGWINCH);
+  }
+#endif
+}
+
+void InstallSignalHandler(int sig) {
+  auto old_signal_handler = std::signal(sig, RecordSignal);
+  on_exit_functions.push(
+      [=] { std::ignore = std::signal(sig, old_signal_handler); });
+};
+
 const std::string CSI = "\x1b[";  // NOLINT
 
 // DEC: Digital Equipment Corporation
@@ -230,31 +296,6 @@ std::string DeviceStatusReport(DSRMode ps) {
   return CSI + std::to_string(int(ps)) + "n";
 }
 
-using SignalHandler = void(int);
-std::stack<Closure> on_exit_functions;  // NOLINT
-void OnExit(int signal) {
-  (void)signal;
-  while (!on_exit_functions.empty()) {
-    on_exit_functions.top()();
-    on_exit_functions.pop();
-  }
-}
-
-const auto install_signal_handler = [](int sig, SignalHandler handler) {
-  auto old_signal_handler = std::signal(sig, handler);
-  on_exit_functions.push(
-      [=] { std::ignore = std::signal(sig, old_signal_handler); });
-};
-
-Closure g_on_resize = [] {};  // NOLINT
-void OnResize(int /* signal */) {
-  g_on_resize();
-}
-
-void OnSigStop(int /*signal*/) {
-  ScreenInteractive::Private::SigStop(*g_active_screen);
-}
-
 class CapturedMouseImpl : public CapturedMouseInterface {
  public:
   explicit CapturedMouseImpl(std::function<void(void)> callback)
@@ -378,10 +419,13 @@ void ScreenInteractive::PreMain() {
   // Suspend previously active screen:
   if (g_active_screen) {
     std::swap(suspended_screen_, g_active_screen);
-    std::cout << suspended_screen_->reset_cursor_position
-              << suspended_screen_->ResetPosition(/*clear=*/true);
+    // Reset cursor position to the top of the screen and clear the screen.
+    suspended_screen_->ResetCursorPosition();
+    std::cout << suspended_screen_->ResetPosition(/*clear=*/true);
     suspended_screen_->dimx_ = 0;
     suspended_screen_->dimy_ = 0;
+
+    // Reset dimensions to force drawing the screen again next time:
     suspended_screen_->Uninstall();
   }
 
@@ -393,20 +437,22 @@ void ScreenInteractive::PreMain() {
 }
 
 void ScreenInteractive::PostMain() {
-  g_active_screen->Uninstall();
-  g_active_screen = nullptr;
-
   // Put cursor position at the end of the drawing.
-  std::cout << reset_cursor_position;
+  ResetCursorPosition();
+
+  g_active_screen = nullptr;
 
   // Restore suspended screen.
   if (suspended_screen_) {
+    // Clear screen, and put the cursor at the beginning of the drawing.
     std::cout << ResetPosition(/*clear=*/true);
     dimx_ = 0;
     dimy_ = 0;
+    Uninstall();
     std::swap(g_active_screen, suspended_screen_);
     g_active_screen->Install();
   } else {
+    Uninstall();
     // On final exit, keep the current drawing and reset cursor position one
     // line after it.
     std::cout << std::endl;
@@ -430,6 +476,8 @@ ScreenInteractive* ScreenInteractive::Active() {
 }
 
 void ScreenInteractive::Install() {
+  frame_valid_ = false;
+
   // After uninstalling the new configuration, flush it to the terminal to
   // ensure it is fully applied:
   on_exit_functions.push([] { Flush(); });
@@ -439,7 +487,7 @@ void ScreenInteractive::Install() {
   // Install signal handlers to restore the terminal state on exit. The default
   // signal handlers are restored on exit.
   for (int signal : {SIGTERM, SIGSEGV, SIGINT, SIGILL, SIGABRT, SIGFPE}) {
-    install_signal_handler(signal, OnExit);
+    InstallSignalHandler(signal);
   }
 
 // Save the old terminal configuration and restore it on exit.
@@ -474,6 +522,10 @@ void ScreenInteractive::Install() {
   SetConsoleMode(stdin_handle, in_mode);
   SetConsoleMode(stdout_handle, out_mode);
 #else
+  for (int signal : {SIGWINCH, SIGTSTP}) {
+    InstallSignalHandler(signal);
+  }
+
   struct termios terminal;  // NOLINT
   tcgetattr(STDIN_FILENO, &terminal);
   on_exit_functions.push([=] { tcsetattr(STDIN_FILENO, TCSANOW, &terminal); });
@@ -488,12 +540,6 @@ void ScreenInteractive::Install() {
 
   tcsetattr(STDIN_FILENO, TCSANOW, &terminal);
 
-  // Handle resize.
-  g_on_resize = [&] { task_sender_->Send(Event::Special({0})); };
-  install_signal_handler(SIGWINCH, OnResize);
-
-  // Handle SIGTSTP/SIGCONT.
-  install_signal_handler(SIGTSTP, OnSigStop);
 #endif
 
   auto enable = [&](const std::vector<DECMode>& parameters) {
@@ -529,8 +575,8 @@ void ScreenInteractive::Install() {
       DECMode::kMouseSgrExtMode,
   });
 
-  // After installing the new configuration, flush it to the terminal to ensure
-  // it is fully applied:
+  // After installing the new configuration, flush it to the terminal to
+  // ensure it is fully applied:
   Flush();
 
   quit_ = false;
@@ -542,28 +588,27 @@ void ScreenInteractive::Install() {
 }
 
 void ScreenInteractive::Uninstall() {
-  ExitLoopClosure()();
+  ExitNow();
   event_listener_.join();
   animation_listener_.join();
-
-  OnExit(0);
+  OnExit();
 }
 
 // NOLINTNEXTLINE
 void ScreenInteractive::RunOnceBlocking(Component component) {
+  ExecuteSignalHandlers();
   Task task;
   if (task_receiver_->Receive(&task)) {
     HandleTask(component, task);
   }
-
   RunOnce(component);
 }
 
-// NOLINTNEXTLINE
 void ScreenInteractive::RunOnce(Component component) {
   Task task;
   while (task_receiver_->ReceiveNonBlocking(&task)) {
     HandleTask(component, task);
+    ExecuteSignalHandlers();
   }
   Draw(std::move(component));
 }
@@ -650,7 +695,8 @@ void ScreenInteractive::Draw(Component component) {
   }
 
   bool resized = (dimx != dimx_) || (dimy != dimy_);
-  std::cout << reset_cursor_position << ResetPosition(/*clear=*/resized);
+  ResetCursorPosition();
+  std::cout << ResetPosition(/*clear=*/resized);
 
   // Resize the screen if needed.
   if (resized) {
@@ -710,7 +756,8 @@ void ScreenInteractive::Draw(Component component) {
       set_cursor_position += "\033[?25l";
     } else {
       set_cursor_position += "\033[?25h";
-      set_cursor_position += "\033[" + std::to_string(int(cursor_.shape)) + " q";
+      set_cursor_position +=
+          "\033[" + std::to_string(int(cursor_.shape)) + " q";
     }
   }
 
@@ -720,32 +767,50 @@ void ScreenInteractive::Draw(Component component) {
   frame_valid_ = true;
 }
 
+void ScreenInteractive::ResetCursorPosition() {
+  std::cout << reset_cursor_position;
+  reset_cursor_position = "";
+}
+
 Closure ScreenInteractive::ExitLoopClosure() {
   return [this] { Exit(); };
 }
 
 void ScreenInteractive::Exit() {
-  Post([this] {
-    quit_ = true;
-    task_sender_.reset();
-  });
+  Post([this] { ExitNow(); });
 }
 
-void ScreenInteractive::SigStop() {
-#if defined(_WIN32)
-  // Windows do no support SIGTSTP.
-#else
+void ScreenInteractive::ExitNow() {
+  quit_ = true;
+  task_sender_.reset();
+}
+
+void ScreenInteractive::Signal(int signal) {
+  if (signal == SIGABRT) {
+    OnExit();
+    return;
+  }
+
+// Windows do no support SIGTSTP / SIGWINCH
+#if !defined(_WIN32)
+  if (signal == SIGTSTP) {
     Post([&] {
+      ResetCursorPosition();
+      std::cout << ResetPosition(/*clear*/ true);  // Cursor to the beginning
       Uninstall();
-    std::cout << reset_cursor_position;
-    reset_cursor_position = "";
-    std::cout << ResetPosition(/*clear=*/true);
       dimx_ = 0;
       dimy_ = 0;
       Flush();
       std::ignore = std::raise(SIGTSTP);
       Install();
     });
+    return;
+  }
+
+  if (signal == SIGWINCH) {
+    Post(Event::Special({0}));
+    return;
+  }
 #endif
 }