Correct crash when read from ogr file in thread (QgsProcessing for instance)

fixes #20581

(cherry picked from commit e948120)

Author: troopa81

src/providers/ogr/qgsogrconnpool.h

@@ -156,7 +156,7 @@ class QgsOgrConnPool : public QgsConnectionPool<QgsOgrConn *, QgsOgrConnPoolGrou
 
       if ( it.value()->unref() )
       {
-        delete it.value();
+        it.value()->deleteLater();
         mGroups.erase( it );
       }
       mMutex.unlock();

tests/src/providers/CMakeLists.txt

@@ -70,6 +70,7 @@ TARGET_LINK_LIBRARIES(qgis_arcgisrestutilstest arcgisfeatureserverprovider_a)
 
 ADD_QGIS_TEST(gdalprovidertest testqgsgdalprovider.cpp)
 
+SET(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -pthread")
 ADD_QGIS_TEST(ogrprovidertest testqgsogrprovider.cpp)
 
 ADD_QGIS_TEST(wmscapabilitiestest

tests/src/providers/testqgsogrprovider.cpp

@@ -45,6 +45,7 @@ class TestQgsOgrProvider : public QObject
     void cleanup() {}// will be called after every testfunction.
 
     void setupProxy();
+    void testThread();
 
   private:
     QString mTestDataDir;
@@ -119,6 +120,87 @@ void TestQgsOgrProvider::setupProxy()
 
 }
 
+class ReadVectorLayer : public QThread
+{
+
+  public :
+    ReadVectorLayer( const QString &filePath, QMutex &mutex, QWaitCondition &waitForVlCreation, QWaitCondition &waitForProcessEvents )
+      : _filePath( filePath ), _mutex( mutex ), _waitForVlCreation( waitForVlCreation ), _waitForProcessEvents( waitForProcessEvents ) {}
+
+    void run() override
+    {
+
+      QgsVectorLayer *vl2 = new QgsVectorLayer( _filePath, QStringLiteral( "thread_test" ), QLatin1Literal( "ogr" ) );
+
+      QgsFeature f;
+      QVERIFY( vl2->getFeatures().nextFeature( f ) );
+
+      _mutex.lock();
+      _waitForVlCreation.wakeAll();
+      _mutex.unlock();
+
+      _mutex.lock();
+      _waitForProcessEvents.wait( &_mutex );
+      _mutex.unlock();
+
+      delete vl2;
+    }
+
+  private:
+    QString _filePath;
+    QMutex &_mutex;
+    QWaitCondition &_waitForVlCreation;
+    QWaitCondition &_waitForProcessEvents;
+
+};
+
+void failOnWarning( QtMsgType type, const QMessageLogContext &context, const QString &msg )
+{
+  Q_UNUSED( context );
+
+  switch ( type )
+  {
+    case QtWarningMsg:
+      QFAIL( QString( "No Qt warning message expect : %1" ).arg( msg ).toUtf8() );
+    default:;
+  }
+}
+
+void TestQgsOgrProvider::testThread()
+{
+  // After reading a QgsVectorLayer (getFeatures) from another thread the QgsOgrConnPoolGroup starts
+  // an expiration timer. The timer belongs to the main thread in order to listening the event
+  // loop and is parented to its QgsOgrConnPoolGroup. So when we delete the QgsVectorLayer, the
+  // QgsConnPoolGroup and the timer are subsequently deleted from another thread. This leads to
+  // segfault later when the expiration time reaches its timeout.
+
+  QMutex mutex;
+  QWaitCondition waitForVlCreation;
+  QWaitCondition waitForProcessEvents;
+
+  QString filePath = mTestDataDir + '/' + QStringLiteral( "lines.shp" );
+  QThread *thread = new ReadVectorLayer( filePath, mutex, waitForVlCreation, waitForProcessEvents );
+
+  thread->start();
+
+  mutex.lock();
+  waitForVlCreation.wait( &mutex );
+  mutex.unlock();
+
+  // make sure timer as been started
+  QCoreApplication::processEvents();
+
+  qInstallMessageHandler( failOnWarning );
+
+  mutex.lock();
+  waitForProcessEvents.wakeAll();
+  mutex.unlock();
+
+  thread->wait();
+  qInstallMessageHandler( 0 );
+
+}
+
 
 QGSTEST_MAIN( TestQgsOgrProvider )
 #include "testqgsogrprovider.moc"