simple static queue for indexing

src/providers/pdal/qgspdalprovider.cpp

@@ -35,6 +35,8 @@
 #define PROVIDER_KEY QStringLiteral( "pdal" )
 #define PROVIDER_DESCRIPTION QStringLiteral( "PDAL point cloud data provider" )
 
+QQueue<QgsPdalProvider *> QgsPdalProvider::mIndexingQueue;
+
 QgsPdalProvider::QgsPdalProvider(
   const QString &uri,
   const QgsDataProvider::ProviderOptions &options,
@@ -93,6 +95,7 @@ void QgsPdalProvider::generateIndex()
   if ( anyIndexingTaskExists() )
   {
     QgsMessageLog::logMessage( tr( "EPT generation task is already running" ), QObject::tr( "Point clouds" ), Qgis::Info );
+    mIndexingQueue.push_back( this );
     return;
   }
 
@@ -146,6 +149,8 @@ void QgsPdalProvider::onGenerateIndexFinished()
     mRunningIndexingTask = nullptr;
     emit indexGenerationStateChanged( PointCloudIndexGenerationState::Indexed );
   }
+  if ( !mIndexingQueue.empty() )
+    mIndexingQueue.takeFirst()->generateIndex();
 }
 
 void QgsPdalProvider::onGenerateIndexFailed()
@@ -157,6 +162,8 @@ void QgsPdalProvider::onGenerateIndexFailed()
     mRunningIndexingTask = nullptr;
     emit indexGenerationStateChanged( PointCloudIndexGenerationState::NotIndexed );
   }
+  if ( !mIndexingQueue.empty() )
+    mIndexingQueue.takeFirst()->generateIndex();
 }
 
 bool QgsPdalProvider::anyIndexingTaskExists()

src/providers/pdal/qgspdalprovider.h

@@ -66,6 +66,7 @@ class QgsPdalProvider: public QgsPointCloudDataProvider
     QVariantMap mOriginalMetadata;
     std::unique_ptr<QgsEptPointCloudIndex> mIndex;
     QgsPdalEptGenerationTask *mRunningIndexingTask = nullptr;
+    static QQueue<QgsPdalProvider *> mIndexingQueue;
 };
 
 class QgsPdalProviderMetadata : public QgsProviderMetadata