Fix race condition in generator.cpp

The check whether to allocate a new QMutex was unprotected.
Two threads may check and allocate concurrently, but only one pointer gets
remembered, the other one will leak. In worst case the returned
mutex is different for two threads, so that two threads try to
synchronize by using two different mutexes.

core/generator.cpp

@@ -41,7 +41,7 @@ using namespace Okular;
 GeneratorPrivate::GeneratorPrivate()
     : m_document( nullptr ),
       mPixmapGenerationThread( nullptr ), mTextPageGenerationThread( nullptr ),
-      m_mutex( nullptr ), m_threadsMutex( nullptr ), mPixmapReady( true ), mTextPageReady( true ),
+      mPixmapReady( true ), mTextPageReady( true ),
       m_closing( false ), m_closingLoop( nullptr ),
       m_dpi(72.0, 72.0)
 {
@@ -59,9 +59,6 @@ GeneratorPrivate::~GeneratorPrivate()
         mTextPageGenerationThread->wait();
 
     delete mTextPageGenerationThread;
-
-    delete m_mutex;
-    delete m_threadsMutex;
 }
 
 PixmapGenerationThread* GeneratorPrivate::pixmapGenerationThread()
@@ -163,9 +160,7 @@ void GeneratorPrivate::textpageGenerationFinished()
 
 QMutex* GeneratorPrivate::threadsLock()
 {
-    if ( !m_threadsMutex )
-        m_threadsMutex = new QMutex();
-    return m_threadsMutex;
+    return &m_threadsMutex;
 }
 
 QVariant GeneratorPrivate::metaData( const QString &, const QVariant & ) const
@@ -508,11 +503,7 @@ QVariant Generator::documentMetaData( const DocumentMetaDataKey key, const QVari
 QMutex* Generator::userMutex() const
 {
     Q_D( const Generator );
-    if ( !d->m_mutex )
-    {
-        d->m_mutex = new QMutex();
-    }
-    return d->m_mutex;
+    return &d->m_mutex;
 }
 
 void Generator::updatePageBoundingBox( int page, const NormalizedRect & boundingBox )

core/generator_p.h

@@ -15,12 +15,12 @@
 
 #include "area.h"
 
+#include <QMutex>
 #include <QSet>
 #include <QThread>
 #include <QImage>
 
 class QEventLoop;
-class QMutex;
 
 #include "generator.h"
 #include "page.h"
@@ -65,8 +65,8 @@ class GeneratorPrivate
         QSet< int > m_features;
         PixmapGenerationThread *mPixmapGenerationThread;
         TextPageGenerationThread *mTextPageGenerationThread;
-        mutable QMutex *m_mutex;
-        QMutex *m_threadsMutex;
+        mutable QMutex m_mutex;
+        QMutex m_threadsMutex;
         bool mPixmapReady : 1;
         bool mTextPageReady : 1;
         bool m_closing : 1;