From ced5910bc8da3a18e037b382ca43c61a88adc10c Mon Sep 17 00:00:00 2001
From: Nyall Dawson <nyall.dawson@gmail.com>
Date: Fri, 2 Jul 2021 08:43:46 +1000
Subject: [PATCH] Fix race

---
 .../providers/qgsprovidersublayertask.sip.in              | 7 +++++--
 src/core/providers/qgsprovidersublayertask.cpp            | 8 +++++++-
 src/core/providers/qgsprovidersublayertask.h              | 8 +++++++-
 3 files changed, 19 insertions(+), 4 deletions(-)

diff --git a/python/core/auto_generated/providers/qgsprovidersublayertask.sip.in b/python/core/auto_generated/providers/qgsprovidersublayertask.sip.in
index 47e713f7935..cfaafb4db6f 100644
--- a/python/core/auto_generated/providers/qgsprovidersublayertask.sip.in
+++ b/python/core/auto_generated/providers/qgsprovidersublayertask.sip.in
@@ -48,11 +48,14 @@ specified ``uri``.
 Returns the sublayer details as calculated by the task.
 %End
 
-    virtual bool run();
-
     virtual void cancel();
 
 
+  protected:
+
+    virtual bool run();
+
+
 };
 
 /************************************************************************
diff --git a/src/core/providers/qgsprovidersublayertask.cpp b/src/core/providers/qgsprovidersublayertask.cpp
index 2f5410dab75..e15c0721ed8 100644
--- a/src/core/providers/qgsprovidersublayertask.cpp
+++ b/src/core/providers/qgsprovidersublayertask.cpp
@@ -19,6 +19,7 @@
 #include "qgsfeedback.h"
 #include "qgsproviderregistry.h"
 #include "qgsprovidersublayerdetails.h"
+#include "qgsreadwritelocker.h"
 
 QgsProviderSublayerTask::QgsProviderSublayerTask( const QString &uri )
   : QgsTask( tr( "Retrieving layers" ), QgsTask::CanCancel | QgsTask::CancelWithoutPrompt )
@@ -28,6 +29,7 @@ QgsProviderSublayerTask::QgsProviderSublayerTask( const QString &uri )
 
 QList<QgsProviderSublayerDetails> QgsProviderSublayerTask::results() const
 {
+  QgsReadWriteLocker locker( mLock, QgsReadWriteLocker::Read );
   return mResults;
 }
 
@@ -37,7 +39,11 @@ bool QgsProviderSublayerTask::run()
 {
   mFeedback = std::make_unique< QgsFeedback >();
 
-  mResults = QgsProviderRegistry::instance()->querySublayers( mUri, Qgis::SublayerQueryFlag::ResolveGeometryType | Qgis::SublayerQueryFlag::CountFeatures, mFeedback.get() );
+  const QList<QgsProviderSublayerDetails> res = QgsProviderRegistry::instance()->querySublayers( mUri, Qgis::SublayerQueryFlag::ResolveGeometryType | Qgis::SublayerQueryFlag::CountFeatures, mFeedback.get() );
+
+  QgsReadWriteLocker locker( mLock, QgsReadWriteLocker::Write );
+  mResults = res;
+
   return true;
 }
 
diff --git a/src/core/providers/qgsprovidersublayertask.h b/src/core/providers/qgsprovidersublayertask.h
index 6eef48dbc11..4fa3082eb69 100644
--- a/src/core/providers/qgsprovidersublayertask.h
+++ b/src/core/providers/qgsprovidersublayertask.h
@@ -19,6 +19,7 @@
 #define QGSPROVIDERSUBLAYERTASKTASK_H
 
 #include "qgstaskmanager.h"
+#include <QReadWriteLock>
 #include <memory>
 
 class QgsFeedback;
@@ -61,9 +62,12 @@ class CORE_EXPORT QgsProviderSublayerTask : public QgsTask
      */
     QList<QgsProviderSublayerDetails> results() const;
 
-    bool run() override;
     void cancel() override;
 
+  protected:
+
+    bool run() override;
+
   private:
 
     QString mUri;
@@ -72,6 +76,8 @@ class CORE_EXPORT QgsProviderSublayerTask : public QgsTask
 
     QList<QgsProviderSublayerDetails> mResults;
 
+    mutable QReadWriteLock mLock;
+
 };
 
 #endif // QGSPROVIDERSUBLAYERTASKTASK_H