fix: keep event handlers alive during dispatch

src/lib/base/EventQueue.cpp

@@ -167,12 +167,12 @@ bool EventQueue::getEvent(Event &event, double timeout)
 bool EventQueue::dispatchEvent(const Event &event)
 {
   void *target = event.getTarget();
-  if (const auto *type_handler = getHandler(event.getType(), target); type_handler) {
-    (*type_handler)(event);
+  if (auto typeHandler = getHandler(event.getType(), target); typeHandler.has_value()) {
+    (*typeHandler)(event);
     return true;
   }
-  if (const auto *any_handler = getHandler(EventTypes::Unknown, target); any_handler) {
-    (*any_handler)(event);
+  if (auto anyHandler = getHandler(EventTypes::Unknown, target); anyHandler.has_value()) {
+    (*anyHandler)(event);
     return true;
   }
   return false;
@@ -295,17 +295,17 @@ void EventQueue::removeHandlers(void *target)
   }
 }
 
-const EventQueue::EventHandler *EventQueue::getHandler(EventTypes type, void *target) const
+std::optional<EventQueue::EventHandler> EventQueue::getHandler(EventTypes type, void *target) const
 {
   std::scoped_lock lock{m_mutex};
   if (HandlerTable::const_iterator index = m_handlers.find(target); index != m_handlers.end()) {
     const TypeHandlerTable &typeHandlers = index->second;
     TypeHandlerTable::const_iterator index2 = typeHandlers.find(type);
     if (index2 != typeHandlers.end()) {
-      return &index2->second;
+      return index2->second;
     }
   }
-  return nullptr;
+  return std::nullopt;
 }
 
 uint32_t EventQueue::saveEvent(Event &&event)

src/lib/base/EventQueue.h

@@ -16,6 +16,7 @@
 #include <map>
 #include <memory>
 #include <mutex>
+#include <optional>
 #include <queue>
 #include <set>
 
@@ -50,7 +51,7 @@ public:
   void waitForReady() const override;
 
 private:
-  const EventHandler *getHandler(EventTypes type, void *target) const;
+  std::optional<EventHandler> getHandler(EventTypes type, void *target) const;
   uint32_t saveEvent(Event &&event);
   Event removeEvent(uint32_t eventID);
   bool hasTimerExpired(Event &event);

src/lib/base/IEventQueue.h

@@ -67,8 +67,8 @@ public:
   Looks up the dispatcher for the event's target and invokes it.
   Returns true iff a dispatcher exists for the target.
 
-  The caller must ensure that the target of the event is not removed by removeHandler() or
-  removeHandlers().
+  The handler may unregister itself while running. The event target object must remain alive until
+  the handler starts.
   */
   virtual bool dispatchEvent(const Event &event) = 0;
 

src/unittests/base/CMakeLists.txt

@@ -37,3 +37,10 @@ create_test(
   WORKING_DIRECTORY "${CMAKE_BINARY_DIR}/src/lib/base"
 )
 
+create_test(
+  NAME EventQueueTests
+  DEPENDS base
+  LIBS arch mt
+  SOURCE EventQueueTests.cpp
+  WORKING_DIRECTORY "${CMAKE_BINARY_DIR}/src/lib/base"
+)

src/unittests/base/EventQueueTests.cpp

@@ -0,0 +1,58 @@
+/*
+ * Deskflow -- mouse and keyboard sharing utility
+ * SPDX-FileCopyrightText: (C) 2026 Deskflow Developers
+ * SPDX-License-Identifier: GPL-2.0-only WITH LicenseRef-OpenSSL-Exception
+ */
+
+#include "EventQueueTests.h"
+
+#include "base/EventQueue.h"
+
+#include <QTest>
+
+#include <memory>
+
+void EventQueueTests::initTestCase()
+{
+  m_arch.init();
+}
+
+void EventQueueTests::dispatchEvent_noHandler_returnsFalse()
+{
+  EventQueue events;
+
+  QVERIFY(!events.dispatchEvent(Event(EventTypes::ClientDisconnected, this)));
+}
+
+void EventQueueTests::dispatchEvent_noTypeHandler_dispatchesUnknownHandler()
+{
+  EventQueue events;
+  bool fallbackCalled = false;
+  events.addHandler(EventTypes::Unknown, this, [&fallbackCalled](const Event &) { fallbackCalled = true; });
+
+  QVERIFY(events.dispatchEvent(Event(EventTypes::ClientDisconnected, this)));
+  QVERIFY(fallbackCalled);
+}
+
+void EventQueueTests::dispatchEvent_handlerRemovesItself_keepsHandlerAliveUntilReturn()
+{
+  EventQueue events;
+  auto handlerLifetime = std::make_shared<int>(1);
+  std::weak_ptr<int> handlerLifetimeObserver = handlerLifetime;
+  bool handlerAliveAfterRemoval = false;
+
+  events.addHandler(
+      EventTypes::ClientDisconnected, this,
+      [this, &events, &handlerLifetimeObserver, &handlerAliveAfterRemoval, handlerLifetime](const Event &) {
+        events.removeHandler(EventTypes::ClientDisconnected, this);
+        handlerAliveAfterRemoval = handlerLifetime != nullptr && !handlerLifetimeObserver.expired();
+      }
+  );
+  handlerLifetime.reset();
+
+  QVERIFY(events.dispatchEvent(Event(EventTypes::ClientDisconnected, this)));
+  QVERIFY(handlerAliveAfterRemoval);
+  QVERIFY(handlerLifetimeObserver.expired());
+}
+
+QTEST_MAIN(EventQueueTests)

src/unittests/base/EventQueueTests.h

@@ -0,0 +1,25 @@
+/*
+ * Deskflow -- mouse and keyboard sharing utility
+ * SPDX-FileCopyrightText: (C) 2026 Deskflow Developers
+ * SPDX-License-Identifier: GPL-2.0-only WITH LicenseRef-OpenSSL-Exception
+ */
+
+#pragma once
+
+#include "arch/Arch.h"
+
+#include <QObject>
+
+class EventQueueTests : public QObject
+{
+  Q_OBJECT
+
+private Q_SLOTS:
+  void initTestCase();
+  void dispatchEvent_noHandler_returnsFalse();
+  void dispatchEvent_noTypeHandler_dispatchesUnknownHandler();
+  void dispatchEvent_handlerRemovesItself_keepsHandlerAliveUntilReturn();
+
+private:
+  Arch m_arch;
+};