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  1. Qt
  2. QTBUG-84463

Q_PLUGIN_INSTANCE macro is not threadsafe

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    Details

    • Type: Bug
    • Status: In Progress
    • Priority: P2: Important
    • Resolution: Unresolved
    • Affects Version/s: 5.12.2, 5.15.0 RC2
    • Fix Version/s: None
    • Component/s: Core: Plugins
    • Labels:
      None
    • Platform/s:
      All

      Description

      The Q_PLUGIN_INSTANCE is not thread safe - while the static block ensures that instance_ is set to null once, it is possible that multiple threads could perform the check that if (!_instance) and then create more than one actual object. (While this is unlikely in practice, our thread sanitizer picked this up)

      By throwing the whole initialization check into a lambda and calling it we don't have this problem

      --- a/src/corelib/plugin/qplugin.h
      +++ b/src/corelib/plugin/qplugin.h
      @@ -129,11 +129,10 @@
       
       #define Q_PLUGIN_INSTANCE(IMPLEMENTATION) \
               { \
      -            static QT_PREPEND_NAMESPACE(QPointer)<QT_PREPEND_NAMESPACE(QObject)> _instance; \
      -            if (!_instance) {    \
      +            static QT_PREPEND_NAMESPACE(QPointer)<QT_PREPEND_NAMESPACE(QObject)> _instance = [] { \
                       QT_PLUGIN_RESOURCE_INIT \
      -                _instance = new IMPLEMENTATION; \
      -            } \
      +                return new IMPLEMENTATION; \
      +            }(); \
                   return _instance; \
               }
       
      

       

        Attachments

        For Gerrit Dashboard: QTBUG-84463
        # Subject Branch Project Status CR V

          Activity

            People

            Assignee:
            thiago Thiago Macieira
            Reporter:
            cwgthornton Chris Thornton
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              Dates

              Created:
              Updated:

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