CoreApplication::processEvents: fix infinite loop

We don't want to end up in an infinite loop if the processing of an events ends up in the posting of another event. Change-Id: I13ba00f41f5204881f6c2da41404b1e0eee9d7a5 Reviewed-on: https://codereview.kdab.com/c/kdab/kdutils/+/136259 Reviewed-by: Sean Harmer <[email protected]> Tested-by: Continuous Integration <[email protected]>
KDAB · Jan 11, 2024 · e9d69ca · e9d69ca
1 parent 72364fc
commit e9d69ca
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Showing 2 changed files with 63 additions and 1 deletion.
diff --git a/src/KDFoundation/core_application.cpp b/src/KDFoundation/core_application.cpp
@@ -94,7 +94,10 @@ void CoreApplication::sendEvent(EventReceiver *target, Event *event)
 void CoreApplication::processEvents(int timeout)
 {
     // Deliver any events that have already been posted
-    while (auto postedEvent = m_eventQueue.tryPop()) {
+    for (size_t eventIndex = 0, eventCount = m_eventQueue.size(); eventIndex < eventCount; ++eventIndex) {
+        auto postedEvent = m_eventQueue.tryPop();
+        if (!postedEvent)
+            break;
         const auto target = postedEvent->target();
         const auto ev = postedEvent->wrappedEvent();
 

diff --git a/tests/auto/foundation/core_application/tst_core_application.cpp b/tests/auto/foundation/core_application/tst_core_application.cpp
@@ -12,6 +12,7 @@
 #include <KDFoundation/config.h>
 #include <KDFoundation/core_application.h>
 #include <KDFoundation/timer.h>
+#include <KDFoundation/event.h>
 #include <KDUtils/logging.h>
 
 #include <condition_variable>
@@ -74,6 +75,37 @@ class EventObject : public Object
     bool m_userEventDelivered = false;
 };
 
+class RecursiveEventPosterObject : public Object
+{
+public:
+    RecursiveEventPosterObject()
+        : Object()
+    {
+    }
+
+    size_t eventsProcessed() const { return m_eventsProcessed; }
+
+    void requestUpdate()
+    {
+        CoreApplication::instance()->postEvent(this, std::make_unique<UpdateEvent>());
+    }
+
+protected:
+    void event(EventReceiver *target, Event *ev) override
+    {
+        if (target == this && ev->type() == Event::Type::Update) {
+            ++m_eventsProcessed;
+            ev->setAccepted(true);
+            requestUpdate();
+        }
+
+        Object::event(target, ev);
+    }
+
+private:
+    size_t m_eventsProcessed{ 0 };
+};
+
 TEST_CASE("Creation")
 {
     SUBCASE("default construction")
@@ -127,6 +159,33 @@ TEST_CASE("Event handling")
 
         app.processEvents();
     }
+
+    SUBCASE("don't end up in infinite loop")
+    {
+        // GIVEN
+        CoreApplication app;
+        auto obj = std::make_unique<RecursiveEventPosterObject>();
+
+        // WHEN
+        obj->requestUpdate();
+        app.processEvents();
+
+        // THEN
+        CHECK(obj->eventsProcessed() == 1);
+
+        // WHEN
+        app.processEvents();
+
+        // THEN
+        CHECK(obj->eventsProcessed() == 2);
+
+        // WHEN
+        for (size_t i = 0; i < 10; ++i)
+            app.processEvents();
+
+        // THEN
+        CHECK(obj->eventsProcessed() == 12);
+    }
 }
 
 #ifndef KD_PLATFORM_MACOS