Add Thread Guard for debugging simple threading issues (#4254)

* Add ThreadGuard class

* Use ThreadGuard when accessing a ChannelView's messageSnapshot

src/CMakeLists.txt

@@ -364,6 +364,7 @@ set(SOURCE_FILES
         util/StreamLink.hpp
         util/StreamerMode.cpp
         util/StreamerMode.hpp
+        util/ThreadGuard.hpp
         util/Twitch.cpp
         util/Twitch.hpp
         util/TypeName.hpp

src/util/ThreadGuard.hpp

@@ -0,0 +1,35 @@
+#pragma once
+
+#include <cassert>
+#include <mutex>
+#include <optional>
+#include <thread>
+
+namespace chatterino {
+
+// Debug-class which asserts if guard of the same object has been called from different threads
+struct ThreadGuard {
+#ifndef NDEBUG
+    std::mutex mutex;
+    std::optional<std::thread::id> threadID;
+#endif
+
+    inline void guard()
+    {
+#ifndef NDEBUG
+        std::unique_lock lock(this->mutex);
+
+        auto currentThreadID = std::this_thread::get_id();
+
+        if (!this->threadID.has_value())
+        {
+            this->threadID = currentThreadID;
+            return;
+        }
+
+        assert(this->threadID == currentThreadID);
+#endif
+    }
+};
+
+}  // namespace chatterino

src/widgets/helper/ChannelView.cpp

@@ -628,6 +628,7 @@ const boost::optional<MessageElementFlags> &ChannelView::getOverrideFlags()
 
 LimitedQueueSnapshot<MessageLayoutPtr> &ChannelView::getMessagesSnapshot()
 {
+    this->snapshotGuard_.guard();
     if (!this->paused() /*|| this->scrollBar_->isVisible()*/)
     {
         this->snapshot_ = this->messages_.getSnapshot();

src/widgets/helper/ChannelView.hpp

@@ -6,6 +6,7 @@
 #include "messages/LimitedQueue.hpp"
 #include "messages/LimitedQueueSnapshot.hpp"
 #include "messages/Selection.hpp"
+#include "util/ThreadGuard.hpp"
 #include "widgets/BaseWidget.hpp"
 
 #include <pajlada/signals/signal.hpp>
@@ -270,6 +271,7 @@ private:
     boost::optional<MessageElementFlags> overrideFlags_;
     MessageLayoutPtr lastReadMessage_;
 
+    ThreadGuard snapshotGuard_;
     LimitedQueueSnapshot<MessageLayoutPtr> snapshot_;
 
     ChannelPtr channel_ = nullptr;