Forward to app blocking/unblocking of attr table updates

Fixes #20094 - Extracting z-coordinates takes ages and makes the system unresponsive

python/core/auto_generated/qgsapplication.sip.in

@@ -824,6 +824,21 @@ Emits the signal to collect all the strings of .qgs to be included in ts file
 .. versionadded:: 3.4
 %End
 
+    void blockAttributeTableUpdates( const QgsVectorLayer *layer );
+%Docstring
+Emits the signal to block updates for attribute tables connected a particular ``layer``
+
+.. versionadded:: 3.4
+%End
+
+    void unblockAttributeTableUpdates( const QgsVectorLayer *layer );
+%Docstring
+Emits the signal to unblock updates for attribute tables connected a particular ``layer``
+
+.. versionadded:: 3.4
+%End
+
+
 %If (ANDROID)
     //dummy method to workaround sip generation issue
     bool x11EventFilter( XEvent *event );
@@ -852,6 +867,21 @@ In order to register translatable strings, connect to this signal and register t
 .. versionadded:: 3.4
 %End
 
+    void attributeTableUpdateBlocked( const QgsVectorLayer *layer );
+%Docstring
+Emitted when attribute table updates for a particular ``layer`` must be blocked
+
+.. versionadded:: 3.4
+%End
+
+    void attributeTableUpdateUnblocked( const QgsVectorLayer *layer );
+%Docstring
+Emitted when all attribute table updates for a particular ``layer`` must be unblocked
+
+.. versionadded:: 3.4
+%End
+
+
 };
 
 

src/app/qgisapp.cpp

@@ -7090,13 +7090,14 @@ void QgisApp::fieldCalculator()
 
 void QgisApp::attributeTable( QgsAttributeTableFilterModel::FilterMode filter )
 {
-  QgsVectorLayer *myLayer = qobject_cast<QgsVectorLayer *>( activeLayer() );
-  if ( !myLayer )
+  QgsVectorLayer *vectorLayer = qobject_cast<QgsVectorLayer *>( activeLayer() );
+  if ( !vectorLayer )
   {
     return;
   }
 
-  QgsAttributeTableDialog *mDialog = new QgsAttributeTableDialog( myLayer, filter );
+  QgsAttributeTableDialog *mDialog = new QgsAttributeTableDialog( vectorLayer, filter );
+
   mDialog->show();
   // the dialog will be deleted by itself on close
 }

src/app/qgsattributetabledialog.cpp

@@ -111,6 +111,18 @@ QgsAttributeTableDialog::QgsAttributeTableDialog( QgsVectorLayer *layer, QgsAttr
   connect( mActionExpressionSelect, &QAction::triggered, this, &QgsAttributeTableDialog::mActionExpressionSelect_triggered );
   connect( mMainView, &QgsDualView::showContextMenuExternally, this, &QgsAttributeTableDialog::showContextMenu );
 
+  // Block/unblock table updates (feature cache signals)
+  connect( QgsApplication::instance(), &QgsApplication::attributeTableUpdateBlocked, [ = ]( const QgsVectorLayer * layer )
+  {
+    if ( layer == mLayer )
+      this->blockCacheUpdateSignals( true );
+  } );
+  connect( QgsApplication::instance(), &QgsApplication::attributeTableUpdateUnblocked, [ = ]( const QgsVectorLayer * layer )
+  {
+    if ( layer == mLayer )
+      this->blockCacheUpdateSignals( false );
+  } );
+
   const QgsFields fields = mLayer->fields();
   for ( const QgsField &field : fields )
   {
@@ -715,20 +727,14 @@ void QgsAttributeTableDialog::mActionOpenFieldCalculator_triggered()
   QgsAttributeTableModel *masterModel = mMainView->masterModel();
 
   QgsFieldCalculator calc( mLayer, this );
-  masterModel->layerCache()->blockSignals( true );
   if ( calc.exec() == QDialog::Accepted )
   {
-    masterModel->layerCache()->blockSignals( false );
     int col = masterModel->fieldCol( calc.changedAttributeId() );
     if ( col >= 0 )
     {
       masterModel->reload( masterModel->index( 0, col ), masterModel->index( masterModel->rowCount() - 1, col ) );
     }
   }
-  else
-  {
-    masterModel->layerCache()->blockSignals( false );
-  }
 }
 
 void QgsAttributeTableDialog::mActionSaveEdits_triggered()
@@ -1135,6 +1141,15 @@ void QgsAttributeTableDialog::setFilterExpression( const QString &filterString,
   mMainView->setFilterMode( QgsAttributeTableFilterModel::ShowFilteredList );
 }
 
+void QgsAttributeTableDialog::blockCacheUpdateSignals( const bool block )
+{
+  QgsAttributeTableModel *masterModel = mMainView->masterModel();
+
+  if ( ! masterModel )
+    return;
+
+  masterModel->layerCache()->blockSignals( block );
+}
 
 void QgsAttributeTableDialog::deleteFeature( const QgsFeatureId fid )
 {

src/app/qgsattributetabledialog.h

@@ -242,6 +242,7 @@ class APP_EXPORT QgsAttributeTableDialog : public QDialog, private Ui::QgsAttrib
 
     void updateMultiEditButtonState();
     void deleteFeature( QgsFeatureId fid );
+    void blockCacheUpdateSignals( const bool block );
 
     friend class TestQgsAttributeTable;
 };

src/app/qgsfieldcalculator.cpp

@@ -267,6 +267,10 @@ void QgsFieldCalculator::accept()
       return;
     }
 
+    // Begin feature modifications, block updates for attr tables
+    // connected to this layer
+    QgsApplication::instance()->blockAttributeTableUpdates( mVectorLayer );
+
     //go through all the features and change the new attribute
     QgsFeature feature;
     bool calculationSuccess = true;
@@ -317,6 +321,8 @@ void QgsFieldCalculator::accept()
       rownum++;
     }
 
+    QgsApplication::instance()->unblockAttributeTableUpdates( mVectorLayer );
+
     QApplication::restoreOverrideCursor();
 
     if ( !calculationSuccess )

src/core/qgsapplication.cpp

@@ -1535,6 +1535,16 @@ void QgsApplication::collectTranslatableObjects( QgsTranslationContext *translat
   emit requestForTranslatableObjects( translationContext );
 }
 
+void QgsApplication::unblockAttributeTableUpdates( const QgsVectorLayer *layer )
+{
+  emit attributeTableUpdateUnblocked( layer );
+}
+
+void QgsApplication::blockAttributeTableUpdates( const QgsVectorLayer *layer )
+{
+  emit attributeTableUpdateBlocked( layer );
+}
+
 QString QgsApplication::nullRepresentation()
 {
   ApplicationMembers *appMembers = members();

src/core/qgsapplication.h

@@ -49,6 +49,7 @@ class QgsLayoutItemRegistry;
 class QgsAuthManager;
 class QgsNetworkContentFetcherRegistry;
 class QTranslator;
+class QgsVectorLayer;
 
 /**
  * \ingroup core
@@ -757,6 +758,21 @@ class CORE_EXPORT QgsApplication : public QApplication
      */
     void collectTranslatableObjects( QgsTranslationContext *translationContext );
 
+    /**
+     * Emits the signal to block updates for attribute tables connected a particular \a layer
+     *
+     * \since QGIS 3.4
+     */
+    void blockAttributeTableUpdates( const QgsVectorLayer *layer );
+
+    /**
+     * Emits the signal to unblock updates for attribute tables connected a particular \a layer
+     *
+     * \since QGIS 3.4
+     */
+    void unblockAttributeTableUpdates( const QgsVectorLayer *layer );
+
+
 #ifdef SIP_RUN
     SIP_IF_FEATURE( ANDROID )
     //dummy method to workaround sip generation issue
@@ -788,6 +804,21 @@ class CORE_EXPORT QgsApplication : public QApplication
      */
     void requestForTranslatableObjects( QgsTranslationContext *translationContext );
 
+    /**
+     * Emitted when attribute table updates for a particular \a layer must be blocked
+     *
+     * \since QGIS 3.4
+     */
+    void attributeTableUpdateBlocked( const QgsVectorLayer *layer );
+
+    /**
+     * Emitted when all attribute table updates for a particular \a layer must be unblocked
+     *
+     * \since QGIS 3.4
+     */
+    void attributeTableUpdateUnblocked( const QgsVectorLayer *layer );
+
+
   private:
 
     static void copyPath( const QString &src, const QString &dst );