Mutex-protect the time conversion in the URLSynchronization to prevent a rare crash when accessing SpiceManager multithreaded

modules/sync/syncs/urlsynchronization.cpp

@@ -222,8 +222,11 @@ bool UrlSynchronization::isEachFileValid() {
     // Valid to: yyyy-mm-ddThr:mn:sc.xxx
 
     if (ossyncVersion == "1.0") {
+        // We need to mutex-protect the access to the time conversion for now
+        std::lock_guard guard(_mutex);
+
         ghoul::getline(file >> std::ws, line);
-        std::string& fileIsValidToDate = line;
+        const std::string& fileIsValidToDate = line;
         const double fileValidAsJ2000 = Time::convertTime(fileIsValidToDate);
 
         const std::string todaysDate = Time::currentWallTime();

modules/sync/syncs/urlsynchronization.h

@@ -122,6 +122,8 @@ private:
 
     /// Determines how long the file is valid before it should be downloaded again
     double _secondsUntilResync = MaxDateAsJ2000;
+
+    std::mutex _mutex;
 };
 
 } // namespace openspace