Fix potential softlock that could happen if the thread was canceled but is not (marked as) terminated

src/BackgroundThread.hpp

@@ -23,6 +23,12 @@ public:
             DCFlushRange(&instance, 4);
         }
     }
+    static void destroyInstance(bool forceKill) {
+        if (instance != nullptr) {
+            instance->skipJoin = true;
+        }
+        destroyInstance();
+    }
 
     BackgroundThread();
 

src/main.cpp

@@ -56,7 +56,9 @@ ON_APPLICATION_START() {
     initLogging();
 
     //Make sure the server instance is destroyed.
-    BackgroundThread::destroyInstance();
+    // Skipping joining the thread as it's not even running at this point but still may be allocated.
+    BackgroundThread::destroyInstance(true);
+    thread = nullptr;
     if (gFTPServerEnabled) {
         startServer();
     }

src/utils/CThread.h

@@ -101,6 +101,9 @@ public:
 
     //! Shutdown thread
     virtual void shutdownThread() {
+        if (skipJoin) {
+            DEBUG_FUNCTION_LINE_WARN("Skip joining the thread \"%s\", it's not running.", pThreadName.c_str());
+        } else {
             //! wait for thread to finish
             if (pThread && !(iAttributes & eAttributeDetach)) {
                 if (!isThreadTerminated()) {
@@ -113,6 +116,7 @@ public:
                     DEBUG_FUNCTION_LINE_WARN("Thread \"%s\" has already been terminated!!!", pThreadName.c_str());
                 }
             }
+        }
         //! free the thread stack buffer
         if (pThreadStack) {
             free(pThreadStack);
@@ -135,6 +139,8 @@ public:
         eAttributePinnedAff = 0x10
     };
 
+    bool skipJoin = false;
+
 private:
     static int threadCallback(int argc, const char **argv) {
         //! After call to start() continue with the internal function