Move most of the QLibraryPrivate initialization to its constructor

This commit moves the setting of the loadHints to inside the constructor
or to QLibraryStore::findOrCreate (which is under a mutex). This avoids
data race conditions with two threads asking for the same plugin at the
same time, with different load hints.

This also opportunistically moves the setting of the error message for
empty file names.

Task-number: QTBUG-39642
Change-Id: I497a41781d10e407d6420116a0b05fdfe2b548de
Reviewed-by: David Faure <david.faure@kdab.com>

src/corelib/plugin/qlibrary.cpp

@@ -359,7 +359,7 @@ class QLibraryStore
 {
 public:
     inline ~QLibraryStore();
-    static inline QLibraryPrivate *findOrCreate(const QString &fileName, const QString &version);
+    static inline QLibraryPrivate *findOrCreate(const QString &fileName, const QString &version, QLibrary::LoadHints loadHints);
     static inline void releaseLibrary(QLibraryPrivate *lib);
 
     static inline void cleanup();
@@ -438,17 +438,21 @@ QLibraryStore *QLibraryStore::instance()
     return qt_library_data;
 }
 
-inline QLibraryPrivate *QLibraryStore::findOrCreate(const QString &fileName, const QString &version)
+inline QLibraryPrivate *QLibraryStore::findOrCreate(const QString &fileName, const QString &version,
+                                                    QLibrary::LoadHints loadHints)
 {
     QMutexLocker locker(&qt_library_mutex);
     QLibraryStore *data = instance();
 
     // check if this library is already loaded
     QLibraryPrivate *lib = 0;
-    if (Q_LIKELY(data))
+    if (Q_LIKELY(data)) {
         lib = data->libraryMap.value(fileName);
+        if (lib)
+            lib->mergeLoadHints(loadHints);
+    }
     if (!lib)
-        lib = new QLibraryPrivate(fileName, version);
+        lib = new QLibraryPrivate(fileName, version, loadHints);
 
     // track this library
     if (Q_LIKELY(data))
@@ -479,21 +483,34 @@ inline void QLibraryStore::releaseLibrary(QLibraryPrivate *lib)
     delete lib;
 }
 
-QLibraryPrivate::QLibraryPrivate(const QString &canonicalFileName, const QString &version)
+QLibraryPrivate::QLibraryPrivate(const QString &canonicalFileName, const QString &version, QLibrary::LoadHints loadHints)
     : pHnd(0), fileName(canonicalFileName), fullVersion(version), instance(0),
-      loadHints(0),
+      loadHints(loadHints),
       libraryRefCount(0), libraryUnloadCount(0), pluginState(MightBeAPlugin)
-{ }
-
-QLibraryPrivate *QLibraryPrivate::findOrCreate(const QString &fileName, const QString &version)
 {
-    return QLibraryStore::findOrCreate(fileName, version);
+    if (canonicalFileName.isEmpty())
+        errorString = QLibrary::tr("The shared library was not found.");
+}
+
+QLibraryPrivate *QLibraryPrivate::findOrCreate(const QString &fileName, const QString &version,
+                                               QLibrary::LoadHints loadHints)
+{
+    return QLibraryStore::findOrCreate(fileName, version, loadHints);
 }
 
 QLibraryPrivate::~QLibraryPrivate()
 {
 }
 
+void QLibraryPrivate::mergeLoadHints(QLibrary::LoadHints lh)
+{
+    // if the library is already loaded, we can't change the load hints
+    if (pHnd)
+        return;
+
+    loadHints = lh;
+}
+
 QFunctionPointer QLibraryPrivate::resolve(const char *symbol)
 {
     if (!pHnd)

src/corelib/plugin/qlibrary_p.h

@@ -94,7 +94,8 @@ public:
     void release();
     QFunctionPointer resolve(const char *);
 
-    static QLibraryPrivate *findOrCreate(const QString &fileName, const QString &version = QString());
+    static QLibraryPrivate *findOrCreate(const QString &fileName, const QString &version = QString(),
+                                         QLibrary::LoadHints loadHints = 0);
     static QStringList suffixes_sys(const QString &fullVersion);
     static QStringList prefixes_sys();
 
@@ -117,8 +118,9 @@ public:
     }
 
 private:
-    explicit QLibraryPrivate(const QString &canonicalFileName, const QString &version);
+    explicit QLibraryPrivate(const QString &canonicalFileName, const QString &version, QLibrary::LoadHints loadHints);
     ~QLibraryPrivate();
+    void mergeLoadHints(QLibrary::LoadHints loadHints);
 
     bool load_sys();
     bool unload_sys();

src/corelib/plugin/qpluginloader.cpp

@@ -352,11 +352,8 @@ void QPluginLoader::setFileName(const QString &fileName)
     else
         fn = locatePlugin(fileName);
 
-    d = QLibraryPrivate::findOrCreate(fn);
-    d->loadHints = lh;
-    if (fn.isEmpty())
-        d->errorString = QLibrary::tr("The shared library was not found.");
-    else
+    d = QLibraryPrivate::findOrCreate(fn, QString(), lh);
+    if (!fn.isEmpty())
         d->updatePluginState();
 
 #else