system: do not disarm non-repeating timer

code/espurna/main.cpp

@@ -142,11 +142,13 @@ void loop() {
     // One-time callbacks, registered some time during runtime
     // Notice that callback container is LIFO, most recently added
     // callback is called first. Copy to allow container modifications.
-    decltype(internal::once_callbacks) once_callbacks;
-    once_callbacks.swap(internal::once_callbacks);
+    if (!internal::once_callbacks.empty()) {
+        decltype(internal::once_callbacks) once_callbacks;
+        once_callbacks.swap(internal::once_callbacks);
 
-    for (const auto& callback : once_callbacks) {
-        callback();
+        for (const auto& callback : once_callbacks) {
+            callback();
+        }
     }
 
     espurna::time::delay(internal::loop_delay);

code/espurna/system.cpp

@@ -341,9 +341,9 @@ void SystemTimer::start(Duration duration, Callback callback, bool repeat) {
     if (!_timer) {
         _timer.reset(new os_timer_t{});
     }
+    _armed = _timer.get();
 
     _callback = std::move(callback);
-    _armed = _timer.get();
     _repeat = repeat;
 
     os_timer_setfn(_timer.get(),
@@ -372,10 +372,14 @@ void SystemTimer::start(Duration duration, Callback callback, bool repeat) {
 void SystemTimer::stop() {
     if (_armed) {
         os_timer_disarm(_armed);
-        _armed = nullptr;
-        _callback = nullptr;
-        _tick = nullptr;
     }
+    reset();
+}
+
+void SystemTimer::reset() {
+    _armed = nullptr;
+    _callback = Callback();
+    _tick = nullptr;
 }
 
 void SystemTimer::callback() {
@@ -395,7 +399,7 @@ void SystemTimer::callback() {
         return;
     }
 
-    stop();
+    reset();
 }
 
 void SystemTimer::schedule_once(Duration duration, Callback callback) {

code/espurna/system.h

@@ -243,6 +243,7 @@ private:
     // with current implementation we use division by 2 until we reach value less than this one
     static constexpr Duration DurationMax = Duration(6870947);
 
+    void reset();
     void start(Duration, Callback, bool repeat);
     void callback();
 
@@ -251,7 +252,8 @@ private:
         size_t count;
     };
 
-    Callback _callback { nullptr };
+    Callback _callback;
+
     os_timer_t* _armed { nullptr };
     bool _repeat { false };