[fix] move keyboard capturer to a background thread and use poll-based X11 event handling to avoid main-thread blocking

src/device_controller/keyboard/linux/keyboard_capturer.cpp

@@ -1,5 +1,8 @@
 #include "keyboard_capturer.h"
 
+#include <errno.h>
+#include <poll.h>
+
 #include "keyboard_converter.h"
 #include "rd_log.h"
 
@@ -10,7 +13,7 @@ static void* g_user_ptr = nullptr;
 
 static int KeyboardEventHandler(Display* display, XEvent* event) {
   if (event->xkey.type == KeyPress || event->xkey.type == KeyRelease) {
-    KeySym keySym = XKeycodeToKeysym(display, event->xkey.keycode, 0);
+    KeySym keySym = XLookupKeysym(&event->xkey, 0);
     int key_code = XKeysymToKeycode(display, keySym);
     bool is_key_down = (event->xkey.type == KeyPress);
 
@@ -21,7 +24,9 @@ static int KeyboardEventHandler(Display* display, XEvent* event) {
   return 0;
 }
 
-KeyboardCapturer::KeyboardCapturer() : display_(nullptr), running_(true) {
+KeyboardCapturer::KeyboardCapturer()
+    : display_(nullptr), root_(0), running_(false) {
+  XInitThreads();
   display_ = XOpenDisplay(nullptr);
   if (!display_) {
     LOG_ERROR("Failed to open X display.");
@@ -29,35 +34,87 @@ KeyboardCapturer::KeyboardCapturer() : display_(nullptr), running_(true) {
 }
 
 KeyboardCapturer::~KeyboardCapturer() {
+  Unhook();
+
   if (display_) {
     XCloseDisplay(display_);
+    display_ = nullptr;
   }
 }
 
 int KeyboardCapturer::Hook(OnKeyAction on_key_action, void* user_ptr) {
+  if (!display_) {
+    LOG_ERROR("Display not initialized.");
+    return -1;
+  }
+
   g_on_key_action = on_key_action;
   g_user_ptr = user_ptr;
 
-  XSelectInput(display_, DefaultRootWindow(display_),
-               KeyPressMask | KeyReleaseMask);
+  if (running_) {
+    return 0;
+  }
 
+  root_ = DefaultRootWindow(display_);
+  XSelectInput(display_, root_, KeyPressMask | KeyReleaseMask);
+  XFlush(display_);
+
+  running_ = true;
+  const int x11_fd = ConnectionNumber(display_);
+  event_thread_ = std::thread([this, x11_fd]() {
     while (running_) {
+      while (running_ && XPending(display_) > 0) {
         XEvent event;
         XNextEvent(display_, &event);
         KeyboardEventHandler(display_, &event);
       }
 
+      if (!running_) {
+        break;
+      }
+
+      struct pollfd pfd = {x11_fd, POLLIN, 0};
+      int poll_ret = poll(&pfd, 1, 50);
+      if (poll_ret < 0) {
+        if (errno == EINTR) {
+          continue;
+        }
+        LOG_ERROR("poll for X11 events failed.");
+        running_ = false;
+        break;
+      }
+
+      if (poll_ret == 0) {
+        continue;
+      }
+
+      if ((pfd.revents & (POLLERR | POLLHUP | POLLNVAL)) != 0) {
+        LOG_ERROR("poll got invalid X11 event fd state.");
+        running_ = false;
+        break;
+      }
+
+      if ((pfd.revents & POLLIN) == 0) {
+        continue;
+      }
+    }
+  });
+
   return 0;
 }
 
 int KeyboardCapturer::Unhook() {
+  running_ = false;
+
+  if (event_thread_.joinable()) {
+    event_thread_.join();
+  }
+
   g_on_key_action = nullptr;
   g_user_ptr = nullptr;
 
-  running_ = false;
-
-  if (display_) {
-    XSelectInput(display_, DefaultRootWindow(display_), 0);
+  if (display_ && root_ != 0) {
+    XSelectInput(display_, root_, 0);
     XFlush(display_);
   }
 

src/device_controller/keyboard/linux/keyboard_capturer.h

@@ -11,6 +11,9 @@
 #include <X11/extensions/XTest.h>
 #include <X11/keysym.h>
 
+#include <atomic>
+#include <thread>
+
 #include "device_controller.h"
 
 namespace crossdesk {
@@ -28,7 +31,8 @@ class KeyboardCapturer : public DeviceController {
  private:
   Display* display_;
   Window root_;
-  bool running_;
+  std::atomic<bool> running_;
+  std::thread event_thread_;
 };
 }  // namespace crossdesk
 #endif