From 486007e013629a0a55dc2a3b861e1cfb21fd4910 Mon Sep 17 00:00:00 2001
From: Even Rouault <even.rouault@spatialys.com>
Date: Fri, 24 Sep 2021 00:11:17 +0200
Subject: [PATCH] QgisApp::closeProject(): cancel canvas jobs before closing
 the project, to avoid rendering jobs to access deleted objects (fixes #44144)

---
 python/gui/auto_generated/qgsmapcanvas.sip.in |  1 +
 src/app/qgisapp.cpp                           |  1 +
 src/gui/qgsmapcanvas.cpp                      | 29 ++++++++++++-------
 src/gui/qgsmapcanvas.h                        |  6 ++++
 4 files changed, 27 insertions(+), 10 deletions(-)

diff --git a/python/gui/auto_generated/qgsmapcanvas.sip.in b/python/gui/auto_generated/qgsmapcanvas.sip.in
index 0ac4476ca461..a0a7bbbeeded 100644
--- a/python/gui/auto_generated/qgsmapcanvas.sip.in
+++ b/python/gui/auto_generated/qgsmapcanvas.sip.in
@@ -133,6 +133,7 @@ Make sure to remove any rendered images from cache (does nothing if cache is not
 .. versionadded:: 2.4
 %End
 
+
     void waitWhileRendering();
 %Docstring
 Blocks until the rendering job has finished.
diff --git a/src/app/qgisapp.cpp b/src/app/qgisapp.cpp
index 3b77ac47532b..b4f6548ec2d8 100644
--- a/src/app/qgisapp.cpp
+++ b/src/app/qgisapp.cpp
@@ -13387,6 +13387,7 @@ void QgisApp::closeProject()
   // clear out any stuff from project
   mMapCanvas->setLayers( QList<QgsMapLayer *>() );
   mMapCanvas->clearCache();
+  mMapCanvas->cancelJobs();
   mOverviewCanvas->setLayers( QList<QgsMapLayer *>() );
 
   // Avoid unnecessary layer changed handling for each layer removed - instead,
diff --git a/src/gui/qgsmapcanvas.cpp b/src/gui/qgsmapcanvas.cpp
index 2c35cf631dd7..ee5972ae115c 100644
--- a/src/gui/qgsmapcanvas.cpp
+++ b/src/gui/qgsmapcanvas.cpp
@@ -242,12 +242,30 @@ QgsMapCanvas::~QgsMapCanvas()
   }
   mLastNonZoomMapTool = nullptr;
 
+  cancelJobs();
+
+  // delete canvas items prior to deleting the canvas
+  // because they might try to update canvas when it's
+  // already being destructed, ends with segfault
+  qDeleteAll( mScene->items() );
+
+  mScene->deleteLater();  // crashes in python tests on windows
+
+  delete mCache;
+  delete mLabelingResults;
+}
+
+
+void QgsMapCanvas::cancelJobs()
+{
+
   // rendering job may still end up writing into canvas map item
   // so kill it before deleting canvas items
   if ( mJob )
   {
     whileBlocking( mJob )->cancel();
     delete mJob;
+    mJob = nullptr;
   }
 
   QList< QgsMapRendererQImageJob * >::const_iterator previewJob = mPreviewJobs.constBegin();
@@ -259,18 +277,9 @@ QgsMapCanvas::~QgsMapCanvas()
       delete *previewJob;
     }
   }
-
-  // delete canvas items prior to deleting the canvas
-  // because they might try to update canvas when it's
-  // already being destructed, ends with segfault
-  qDeleteAll( mScene->items() );
-
-  mScene->deleteLater();  // crashes in python tests on windows
-
-  delete mCache;
-  delete mLabelingResults;
 }
 
+
 void QgsMapCanvas::setMagnificationFactor( double factor, const QgsPointXY *center )
 {
   // do not go higher or lower than min max magnification ratio
diff --git a/src/gui/qgsmapcanvas.h b/src/gui/qgsmapcanvas.h
index 6bb56a8b8cb2..e45c7582cd76 100644
--- a/src/gui/qgsmapcanvas.h
+++ b/src/gui/qgsmapcanvas.h
@@ -183,6 +183,12 @@ class GUI_EXPORT QgsMapCanvas : public QGraphicsView, public QgsExpressionContex
      */
     void clearCache();
 
+    /**
+     * Cancel any rendering job, in a blocking way. Used for application closing.
+     * \note not available in Python bindings
+     */
+    void cancelJobs() SIP_SKIP;
+
     /**
      * Blocks until the rendering job has finished.
      *