apache · hansva · Aug 31, 2026 · Aug 31, 2026
diff --git a/docs/hop-dev-manual/modules/ROOT/pages/hopweb/hopweb-antipatterns.adoc b/docs/hop-dev-manual/modules/ROOT/pages/hopweb/hopweb-antipatterns.adoc
@@ -171,9 +171,12 @@ Hop Web creates one RAP `UISession` (and one SWT `Display`) per browser session.
 * **Perspectives:** `getInstance()` must prefer `HopGui.findSessionPerspective(...)`. A static `instance` field is only a fallback for tests and disabled perspectives.
 * **Caches of SWT `Image`s:** key by `Device`/`Display` and dispose on *that* device. Never one process-wide dispose hook.
 * **Engine-thread maps (drill-down):** stamp `hopGui.getId()` on the engine in the GUI thread; do not call `HopGui.getInstance()` from pipeline worker threads (no RAP `UISession`).
+* **Background threads started by a dialog:** start them with `BackgroundThreadFacade.start(runnable)` instead of `new Thread(runnable).start()`. A dialog that looks up its input fields in the background reads session state while doing so (`ConstUi.sortFieldNames` asks `PropsUi`), and a plain thread has no `UISession` to read it from.
 
 Do not store `Control`, `Shell`, `SashForm`, `Image`, `Color`, `Font` or `GC` in `static` fields. When session A ends RAP disposes those objects; session B then hits `Invalid thread access` or `Widget is disposed`.
 
+A thread that carries a session is still not the UI thread: widgets stay off limits to it, and it reaches them the same way as before, through `Display.asyncExec`.
+
 == Avoid use of unimplemented SWT APIs
 
 === Example: drawing on an Image

diff --git a/...in/java/org/apache/hop/pipeline/transforms/cratedbbulkloader/CrateDBBulkLoaderDialog.java b/...in/java/org/apache/hop/pipeline/transforms/cratedbbulkloader/CrateDBBulkLoaderDialog.java
@@ -55,6 +55,7 @@
 import org.apache.hop.ui.core.widget.PasswordTextVar;
 import org.apache.hop.ui.core.widget.TableView;
 import org.apache.hop.ui.core.widget.TextVar;
+import org.apache.hop.ui.hopgui.BackgroundThreadFacade;
 import org.apache.hop.ui.pipeline.transform.BaseTransformDialog;
 import org.eclipse.swt.SWT;
 import org.eclipse.swt.custom.CTabFolder;
@@ -382,7 +383,7 @@ public void run() {
             }
           }
         };
-    new Thread(runnable).start();
+    BackgroundThreadFacade.start(runnable);
   }
 
   private void addAwsAuthenticationTab(

diff --git a/...c/main/java/org/apache/hop/pipeline/transforms/dorisbulkloader/DorisBulkLoaderDialog.java b/...c/main/java/org/apache/hop/pipeline/transforms/dorisbulkloader/DorisBulkLoaderDialog.java
@@ -43,6 +43,7 @@
 import org.apache.hop.ui.core.widget.PasswordTextVar;
 import org.apache.hop.ui.core.widget.TableView;
 import org.apache.hop.ui.core.widget.TextVar;
+import org.apache.hop.ui.hopgui.BackgroundThreadFacade;
 import org.apache.hop.ui.pipeline.transform.BaseTransformDialog;
 import org.eclipse.swt.SWT;
 import org.eclipse.swt.custom.CTabFolder;
@@ -570,7 +571,7 @@ public void run() {
             }
           }
         };
-    new Thread(runnable).start();
+    BackgroundThreadFacade.start(runnable);
 
     getData();
     focusTransformName();

diff --git a/...in/java/org/apache/hop/pipeline/transforms/monetdbbulkloader/MonetDbBulkLoaderDialog.java b/...in/java/org/apache/hop/pipeline/transforms/monetdbbulkloader/MonetDbBulkLoaderDialog.java
@@ -48,6 +48,7 @@
 import org.apache.hop.ui.core.widget.MetaSelectionLine;
 import org.apache.hop.ui.core.widget.TableView;
 import org.apache.hop.ui.core.widget.TextVar;
+import org.apache.hop.ui.hopgui.BackgroundThreadFacade;
 import org.apache.hop.ui.pipeline.transform.BaseTransformDialog;
 import org.apache.hop.ui.pipeline.transform.ITableItemInsertListener;
 import org.eclipse.swt.SWT;
@@ -697,7 +698,7 @@ public void widgetSelected(SelectionEvent arg0) {
             }
           }
         };
-    new Thread(runnable).start();
+    BackgroundThreadFacade.start(runnable);
 
     wbLogFile.addListener(
         SWT.Selection,

diff --git a/.../java/org/apache/hop/pipeline/transforms/mssqlbulkloader/MsSqlServerBulkLoaderDialog.java b/.../java/org/apache/hop/pipeline/transforms/mssqlbulkloader/MsSqlServerBulkLoaderDialog.java
@@ -51,6 +51,7 @@
 import org.apache.hop.ui.core.widget.MetaSelectionLine;
 import org.apache.hop.ui.core.widget.TableView;
 import org.apache.hop.ui.core.widget.TextVar;
+import org.apache.hop.ui.hopgui.BackgroundThreadFacade;
 import org.apache.hop.ui.pipeline.transform.BaseTransformDialog;
 import org.eclipse.swt.SWT;
 import org.eclipse.swt.custom.CTabFolder;
@@ -178,23 +179,22 @@ public void focusLost(FocusEvent event) {
     wSettingsComp.layout();
 
     // Look up the incoming fields in the background, they feed the stream field drop-down.
-    new Thread(
-            () -> {
-              TransformMeta stepMeta = pipelineMeta.findTransform(transformName);
-              if (stepMeta == null) {
-                return;
-              }
-              try {
-                IRowMeta row = pipelineMeta.getPrevTransformFields(variables, stepMeta);
-                for (int i = 0; i < row.size(); i++) {
-                  inputFields.put(row.getValueMeta(i).getName(), i);
-                }
-                setComboBoxes();
-              } catch (HopException e) {
-                logError(BaseMessages.getString(PKG, "System.Dialog.GetFieldsFailed.Message"));
-              }
-            })
-        .start();
+    BackgroundThreadFacade.start(
+        () -> {
+          TransformMeta stepMeta = pipelineMeta.findTransform(transformName);
+          if (stepMeta == null) {
+            return;
+          }
+          try {
+            IRowMeta row = pipelineMeta.getPrevTransformFields(variables, stepMeta);
+            for (int i = 0; i < row.size(); i++) {
+              inputFields.put(row.getValueMeta(i).getName(), i);
+            }
+            setComboBoxes();
+          } catch (HopException e) {
+            logError(BaseMessages.getString(PKG, "System.Dialog.GetFieldsFailed.Message"));
+          }
+        });
 
     wContent.pack();
     Rectangle bounds = wContent.getBounds();

diff --git a/...c/main/java/org/apache/hop/pipeline/transforms/mysqlbulkloader/MySqlBulkLoaderDialog.java b/...c/main/java/org/apache/hop/pipeline/transforms/mysqlbulkloader/MySqlBulkLoaderDialog.java
@@ -52,6 +52,7 @@
 import org.apache.hop.ui.core.widget.MetaSelectionLine;
 import org.apache.hop.ui.core.widget.TableView;
 import org.apache.hop.ui.core.widget.TextVar;
+import org.apache.hop.ui.hopgui.BackgroundThreadFacade;
 import org.apache.hop.ui.pipeline.transform.BaseTransformDialog;
 import org.apache.hop.ui.pipeline.transform.ITableItemInsertListener;
 import org.eclipse.swt.SWT;
@@ -568,7 +569,7 @@ public void widgetSelected(SelectionEvent arg0) {
             }
           }
         };
-    new Thread(runnable).start();
+    BackgroundThreadFacade.start(runnable);
 
     wContent.pack();
     Rectangle bounds = wContent.getBounds();

diff --git a/...e/src/main/java/org/apache/hop/pipeline/transforms/orabulkloader/OraBulkLoaderDialog.java b/...e/src/main/java/org/apache/hop/pipeline/transforms/orabulkloader/OraBulkLoaderDialog.java
@@ -51,6 +51,7 @@
 import org.apache.hop.ui.core.widget.MetaSelectionLine;
 import org.apache.hop.ui.core.widget.TableView;
 import org.apache.hop.ui.core.widget.TextVar;
+import org.apache.hop.ui.hopgui.BackgroundThreadFacade;
 import org.apache.hop.ui.pipeline.transform.BaseTransformDialog;
 import org.apache.hop.ui.pipeline.transform.ITableItemInsertListener;
 import org.eclipse.swt.SWT;
@@ -849,7 +850,7 @@ public void widgetSelected(SelectionEvent e) {
             }
           }
         };
-    new Thread(runnable).start();
+    BackgroundThreadFacade.start(runnable);
 
     SelectionListener fileSelectionListener =
         new SelectionAdapter() {

diff --git a/...sql/src/main/java/org/apache/hop/pipeline/transforms/pgbulkloader/PGBulkLoaderDialog.java b/...sql/src/main/java/org/apache/hop/pipeline/transforms/pgbulkloader/PGBulkLoaderDialog.java
@@ -48,6 +48,7 @@
 import org.apache.hop.ui.core.widget.MetaSelectionLine;
 import org.apache.hop.ui.core.widget.TableView;
 import org.apache.hop.ui.core.widget.TextVar;
+import org.apache.hop.ui.hopgui.BackgroundThreadFacade;
 import org.apache.hop.ui.pipeline.transform.BaseTransformDialog;
 import org.apache.hop.ui.pipeline.transform.ITableItemInsertListener;
 import org.eclipse.swt.SWT;
@@ -397,7 +398,7 @@ public void widgetSelected(SelectionEvent e) {
             }
           }
         };
-    new Thread(runnable).start();
+    BackgroundThreadFacade.start(runnable);
 
     // Add listeners
     wGetLU.addListener(SWT.Selection, e -> getUpdate());

diff --git a/...va/org/apache/hop/pipeline/transforms/snowflake/bulkloader/SnowflakeBulkLoaderDialog.java b/...va/org/apache/hop/pipeline/transforms/snowflake/bulkloader/SnowflakeBulkLoaderDialog.java
@@ -54,6 +54,7 @@
 import org.apache.hop.ui.core.widget.MetaSelectionLine;
 import org.apache.hop.ui.core.widget.TableView;
 import org.apache.hop.ui.core.widget.TextVar;
+import org.apache.hop.ui.hopgui.BackgroundThreadFacade;
 import org.apache.hop.ui.pipeline.transform.BaseTransformDialog;
 import org.eclipse.swt.SWT;
 import org.eclipse.swt.custom.CCombo;
@@ -1105,7 +1106,7 @@ public void focusGained(FocusEvent focusEvent) {
             }
           }
         };
-    new Thread(runnable).start();
+    BackgroundThreadFacade.start(runnable);
 
     FormData fdFieldsComp = new FormData();
     fdFieldsComp.left = new FormAttachment(0, 0);

diff --git a/...es/teradata/src/main/java/org/apache/hop/pipeline/transforms/terafast/TeraFastDialog.java b/...es/teradata/src/main/java/org/apache/hop/pipeline/transforms/terafast/TeraFastDialog.java
@@ -43,6 +43,7 @@
 import org.apache.hop.ui.core.widget.PluginWidgetFactory;
 import org.apache.hop.ui.core.widget.TableView;
 import org.apache.hop.ui.core.widget.TextVar;
+import org.apache.hop.ui.hopgui.BackgroundThreadFacade;
 import org.apache.hop.ui.pipeline.transform.BaseTransformDialog;
 import org.apache.hop.ui.pipeline.transform.ITableItemInsertListener;
 import org.eclipse.swt.SWT;
@@ -191,7 +192,7 @@ public String open() {
                 BaseMessages.getString(PKG, "System.Dialog.GetFieldsFailed.Message"));
           }
         };
-    new Thread(runnable).start();
+    BackgroundThreadFacade.start(runnable);
 
     getData();
     this.meta.setChanged(this.changed);

diff --git a/...n/java/org/apache/hop/pipeline/transforms/vertica/bulkloader/VerticaBulkLoaderDialog.java b/...n/java/org/apache/hop/pipeline/transforms/vertica/bulkloader/VerticaBulkLoaderDialog.java
@@ -53,6 +53,7 @@
 import org.apache.hop.ui.core.widget.MetaSelectionLine;
 import org.apache.hop.ui.core.widget.TableView;
 import org.apache.hop.ui.core.widget.TextVar;
+import org.apache.hop.ui.hopgui.BackgroundThreadFacade;
 import org.apache.hop.ui.pipeline.transform.BaseTransformDialog;
 import org.eclipse.swt.SWT;
 import org.eclipse.swt.custom.CTabFolder;
@@ -600,7 +601,7 @@ public void run() {
             }
           }
         };
-    new Thread(runnable).start();
+    BackgroundThreadFacade.start(runnable);
 
     fdTabFolder = new FormData();
     fdTabFolder.left = new FormAttachment(0, 0);

diff --git a/...s/tech/avro/src/main/java/org/apache/hop/avro/transforms/avrooutput/AvroOutputDialog.java b/...s/tech/avro/src/main/java/org/apache/hop/avro/transforms/avrooutput/AvroOutputDialog.java
@@ -41,6 +41,7 @@
 import org.apache.hop.ui.core.widget.ColumnInfo;
 import org.apache.hop.ui.core.widget.TableView;
 import org.apache.hop.ui.core.widget.TextVar;
+import org.apache.hop.ui.hopgui.BackgroundThreadFacade;
 import org.apache.hop.ui.pipeline.transform.BaseTransformDialog;
 import org.apache.hop.ui.pipeline.transform.ITableItemInsertListener;
 import org.eclipse.swt.SWT;
@@ -759,7 +760,7 @@ public void widgetSelected(SelectionEvent arg0) {
             }
           }
         };
-    new Thread(runnable).start();
+    BackgroundThreadFacade.start(runnable);
 
     FormData fdFieldsComp = new FormData();
     fdFieldsComp.left = new FormAttachment(0, 0);

diff --git a/...ns/tech/aws/src/main/java/org/apache/hop/pipeline/transforms/aws/sns/SnsNotifyDialog.java b/...ns/tech/aws/src/main/java/org/apache/hop/pipeline/transforms/aws/sns/SnsNotifyDialog.java
@@ -31,6 +31,7 @@
 import org.apache.hop.ui.core.widget.PasswordTextVar;
 import org.apache.hop.ui.core.widget.TableView;
 import org.apache.hop.ui.core.widget.TextVar;
+import org.apache.hop.ui.hopgui.BackgroundThreadFacade;
 import org.apache.hop.ui.pipeline.transform.BaseTransformDialog;
 import org.eclipse.swt.SWT;
 import org.eclipse.swt.custom.CTabFolder;
@@ -497,7 +498,7 @@ private void setComboValues() {
           Arrays.sort(prevTransformFieldNames);
           fieldColumn.setComboValues(prevTransformFieldNames);
         };
-    new Thread(fieldLoader).start();
+    BackgroundThreadFacade.start(fieldLoader);
   }
 
   /** This method fills the ComboVar with common AWS region IDs (SNS-supported). */

diff --git a/...java/org/apache/hop/pipeline/transforms/redshift/bulkloader/RedshiftBulkLoaderDialog.java b/...java/org/apache/hop/pipeline/transforms/redshift/bulkloader/RedshiftBulkLoaderDialog.java
@@ -55,6 +55,7 @@
 import org.apache.hop.ui.core.widget.MetaSelectionLine;
 import org.apache.hop.ui.core.widget.TableView;
 import org.apache.hop.ui.core.widget.TextVar;
+import org.apache.hop.ui.hopgui.BackgroundThreadFacade;
 import org.apache.hop.ui.pipeline.transform.BaseTransformDialog;
 import org.eclipse.swt.SWT;
 import org.eclipse.swt.custom.CTabFolder;
@@ -738,7 +739,7 @@ public void run() {
             }
           }
         };
-    new Thread(runnable).start();
+    BackgroundThreadFacade.start(runnable);
   }
 
   /**

diff --git a/...b/src/main/java/org/apache/hop/pipeline/transforms/mongodbdelete/MongoDbDeleteDialog.java b/...b/src/main/java/org/apache/hop/pipeline/transforms/mongodbdelete/MongoDbDeleteDialog.java
@@ -50,6 +50,7 @@
 import org.apache.hop.ui.core.widget.TableView;
 import org.apache.hop.ui.core.widget.TextComposite;
 import org.apache.hop.ui.core.widget.TextVar;
+import org.apache.hop.ui.hopgui.BackgroundThreadFacade;
 import org.apache.hop.ui.pipeline.transform.BaseTransformDialog;
 import org.bson.Document;
 import org.eclipse.swt.SWT;
@@ -341,7 +342,7 @@ public void run() {
             }
           }
         };
-    new Thread(runnable).start();
+    BackgroundThreadFacade.start(runnable);
 
     // get fields but
     wbGetFields = new Button(wFieldsComp, SWT.PUSH | SWT.CENTER);

diff --git a/...main/java/org/apache/hop/pipeline/transforms/salesforceinsert/SalesforceInsertDialog.java b/...main/java/org/apache/hop/pipeline/transforms/salesforceinsert/SalesforceInsertDialog.java
@@ -54,6 +54,7 @@
 import org.apache.hop.ui.core.widget.MetaSelectionLine;
 import org.apache.hop.ui.core.widget.TableView;
 import org.apache.hop.ui.core.widget.TextVar;
+import org.apache.hop.ui.hopgui.BackgroundThreadFacade;
 import org.apache.hop.ui.hopgui.HopGui;
 import org.apache.hop.ui.pipeline.transform.BaseTransformDialog;
 import org.apache.hop.ui.pipeline.transform.ComponentSelectionListener;
@@ -566,7 +567,7 @@ public void focusGained(org.eclipse.swt.events.FocusEvent e) {
             }
           }
         };
-    new Thread(runnable).start();
+    BackgroundThreadFacade.start(runnable);
 
     FormData fdGeneralComp = new FormData();
     fdGeneralComp.left = new FormAttachment(0, 0);

diff --git a/...main/java/org/apache/hop/pipeline/transforms/salesforceupdate/SalesforceUpdateDialog.java b/...main/java/org/apache/hop/pipeline/transforms/salesforceupdate/SalesforceUpdateDialog.java
@@ -50,6 +50,7 @@
 import org.apache.hop.ui.core.widget.MetaSelectionLine;
 import org.apache.hop.ui.core.widget.TableView;
 import org.apache.hop.ui.core.widget.TextVar;
+import org.apache.hop.ui.hopgui.BackgroundThreadFacade;
 import org.apache.hop.ui.hopgui.HopGui;
 import org.apache.hop.ui.pipeline.transform.BaseTransformDialog;
 import org.apache.hop.ui.pipeline.transform.ComponentSelectionListener;
@@ -513,7 +514,7 @@ public void focusGained(org.eclipse.swt.events.FocusEvent e) {
             }
           }
         };
-    new Thread(runnable).start();
+    BackgroundThreadFacade.start(runnable);
 
     FormData fdGeneralComp = new FormData();
     fdGeneralComp.left = new FormAttachment(0, 0);

diff --git a/...main/java/org/apache/hop/pipeline/transforms/salesforceupsert/SalesforceUpsertDialog.java b/...main/java/org/apache/hop/pipeline/transforms/salesforceupsert/SalesforceUpsertDialog.java
@@ -52,6 +52,7 @@
 import org.apache.hop.ui.core.widget.MetaSelectionLine;
 import org.apache.hop.ui.core.widget.TableView;
 import org.apache.hop.ui.core.widget.TextVar;
+import org.apache.hop.ui.hopgui.BackgroundThreadFacade;
 import org.apache.hop.ui.hopgui.HopGui;
 import org.apache.hop.ui.pipeline.transform.BaseTransformDialog;
 import org.apache.hop.ui.pipeline.transform.ComponentSelectionListener;
@@ -636,7 +637,7 @@ public void focusLost(FocusEvent e) {
             }
           }
         };
-    new Thread(runnable).start();
+    BackgroundThreadFacade.start(runnable);
 
     FormData fdGeneralComp = new FormData();
     fdGeneralComp.left = new FormAttachment(0, 0);

diff --git a/...y/src/main/java/org/apache/hop/pipeline/transforms/analyticquery/AnalyticQueryDialog.java b/...y/src/main/java/org/apache/hop/pipeline/transforms/analyticquery/AnalyticQueryDialog.java
@@ -34,6 +34,7 @@
 import org.apache.hop.ui.core.dialog.MessageDialogWithToggle;
 import org.apache.hop.ui.core.widget.ColumnInfo;
 import org.apache.hop.ui.core.widget.TableView;
+import org.apache.hop.ui.hopgui.BackgroundThreadFacade;
 import org.apache.hop.ui.pipeline.transform.BaseTransformDialog;
 import org.eclipse.swt.SWT;
 import org.eclipse.swt.events.ModifyListener;
@@ -191,7 +192,7 @@ public String open() {
             }
           }
         };
-    new Thread(runnable).start();
+    BackgroundThreadFacade.start(runnable);
 
     FormData fdAgg = new FormData();
     fdAgg.left = new FormAttachment(0, 0);

diff --git a/...culator/src/main/java/org/apache/hop/pipeline/transforms/calculator/CalculatorDialog.java b/...culator/src/main/java/org/apache/hop/pipeline/transforms/calculator/CalculatorDialog.java
@@ -34,6 +34,7 @@
 import org.apache.hop.ui.core.dialog.EnterSelectionDialog;
 import org.apache.hop.ui.core.widget.ColumnInfo;
 import org.apache.hop.ui.core.widget.TableView;
+import org.apache.hop.ui.hopgui.BackgroundThreadFacade;
 import org.apache.hop.ui.pipeline.transform.BaseTransformDialog;
 import org.apache.hop.ui.util.SwtSvgImageUtil;
 import org.eclipse.swt.SWT;
@@ -226,7 +227,7 @@ public void widgetSelected(SelectionEvent e) {
             }
           }
         };
-    new Thread(runnable).start();
+    BackgroundThreadFacade.start(runnable);
 
     wFields.addModifyListener(
         arg0 ->

diff --git a/...ms/checksum/src/main/java/org/apache/hop/pipeline/transforms/checksum/CheckSumDialog.java b/...ms/checksum/src/main/java/org/apache/hop/pipeline/transforms/checksum/CheckSumDialog.java
@@ -34,6 +34,7 @@
 import org.apache.hop.ui.core.widget.ColumnInfo;
 import org.apache.hop.ui.core.widget.TableView;
 import org.apache.hop.ui.core.widget.TextVar;
+import org.apache.hop.ui.hopgui.BackgroundThreadFacade;
 import org.apache.hop.ui.pipeline.transform.BaseTransformDialog;
 import org.apache.hop.ui.pipeline.transform.ITableItemInsertListener;
 import org.eclipse.swt.SWT;
@@ -262,7 +263,7 @@ public void widgetSelected(SelectionEvent e) {
             }
           }
         };
-    new Thread(runnable).start();
+    BackgroundThreadFacade.start(runnable);
 
     getData();
     activeResultType();