internal: add a watchdog

a watchdog will abort processing a signal if a timeout specified via debug:watchdog_timeout is reached.

src/helpers/Watchdog.hpp

@@ -0,0 +1,30 @@
+#pragma once
+
+#include <memory>
+#include <chrono>
+#include <thread>
+#include <condition_variable>
+
+class CWatchdog {
+  public:
+    // must be called from the main thread
+    CWatchdog();
+
+    void startWatching();
+    void endWatching();
+
+  private:
+    std::chrono::high_resolution_clock::time_point m_tTriggered;
+
+    pthread_t                                      m_iMainThreadPID = 0;
+
+    bool                                           m_bWatching  = false;
+    bool                                           m_bWillWatch = false;
+
+    std::unique_ptr<std::thread>                   m_pWatchdog;
+    std::mutex                                     m_mWatchdogMutex;
+    bool                                           m_bNotified = false;
+    std::condition_variable                        m_cvWatchdogCondition;
+};
+
+inline std::unique_ptr<CWatchdog> g_pWatchdog;