Add handling of dependent layers to task manager

If a task has dependent layers which are about to be removed,
the task will automatically be cancelled

Author: nyalldawson

python/core/qgstaskmanager.sip

@@ -219,6 +219,22 @@ class QgsTaskManager : QObject
     //! Will return true if the specified task has circular dependencies
     bool hasCircularDependencies( long taskId ) const;
 
+    /** Sets a list of layers on which as task is dependent. The task will automatically
+     * be cancelled if any of these layers are above to be removed.
+     * @param taskId task ID
+     * @param layerIds list of layer IDs
+     * @see dependentLayers()
+     */
+    void setDependentLayers( long taskId, const QStringList& layerIds );
+
+    /** Returns a list of layers on which as task is dependent. The task will automatically
+     * be cancelled if any of these layers are above to be removed.
+     * @param taskId task ID
+     * @returns list of layer IDs
+     * @see setDependentLayers()
+     */
+    QStringList dependentLayers( long taskId ) const;
+
   signals:
 
     //! Will be emitted when a task reports a progress change

src/core/qgstaskmanager.cpp

@@ -16,6 +16,7 @@
  ***************************************************************************/
 
 #include "qgstaskmanager.h"
+#include "qgsmaplayerregistry.h"
 #include <QtConcurrentRun>
 
 
@@ -108,7 +109,10 @@ QgsTaskManager *QgsTaskManager::instance()
 QgsTaskManager::QgsTaskManager( QObject* parent )
     : QObject( parent )
     , mNextTaskId( 0 )
-{}
+{
+  connect( QgsMapLayerRegistry::instance(), SIGNAL( layersWillBeRemoved( QStringList ) ),
+           this, SLOT( layersWillBeRemoved( QStringList ) ) );
+}
 
 QgsTaskManager::~QgsTaskManager()
 {
@@ -276,6 +280,16 @@ bool QgsTaskManager::hasCircularDependencies( long taskId ) const
   return !resolveDependencies( taskId, taskId, d );
 }
 
+void QgsTaskManager::setDependentLayers( long taskId, const QStringList& layerIds )
+{
+  mLayerDependencies.insert( taskId, layerIds );
+}
+
+QStringList QgsTaskManager::dependentLayers( long taskId ) const
+{
+  return mLayerDependencies.value( taskId, QStringList() );
+}
+
 void QgsTaskManager::taskProgressChanged( double progress )
 {
   QgsTask* task = qobject_cast< QgsTask* >( sender() );
@@ -307,6 +321,31 @@ void QgsTaskManager::taskStatusChanged( int status )
   processQueue();
 }
 
+void QgsTaskManager::layersWillBeRemoved( const QStringList& layerIds )
+{
+  // scan through layers to be removed
+  Q_FOREACH ( const QString& layerId, layerIds )
+  {
+    // scan through tasks with layer dependencies
+    for ( QMap< long, QStringList >::const_iterator it = mLayerDependencies.constBegin();
+          it != mLayerDependencies.constEnd(); ++it )
+    {
+      if ( !it.value().contains( layerId ) )
+      {
+        //task not dependent on this layer
+        continue;
+      }
+
+      QgsTask* dependentTask = task( it.key() );
+      if ( dependentTask && ( dependentTask->status() != QgsTask::Complete || dependentTask->status() != QgsTask::Terminated ) )
+      {
+        // incomplete task is dependent on this layer!
+        dependentTask->cancel();
+      }
+    }
+  }
+}
+
 bool QgsTaskManager::cleanupAndDeleteTask( QgsTask *task )
 {
   if ( !task )

src/core/qgstaskmanager.h

@@ -250,6 +250,22 @@ class CORE_EXPORT QgsTaskManager : public QObject
     //! Will return true if the specified task has circular dependencies
     bool hasCircularDependencies( long taskId ) const;
 
+    /** Sets a list of layers on which as task is dependent. The task will automatically
+     * be cancelled if any of these layers are above to be removed.
+     * @param taskId task ID
+     * @param layerIds list of layer IDs
+     * @see dependentLayers()
+     */
+    void setDependentLayers( long taskId, const QStringList& layerIds );
+
+    /** Returns a list of layers on which as task is dependent. The task will automatically
+     * be cancelled if any of these layers are above to be removed.
+     * @param taskId task ID
+     * @returns list of layer IDs
+     * @see setDependentLayers()
+     */
+    QStringList dependentLayers( long taskId ) const;
+
   signals:
 
     //! Will be emitted when a task reports a progress change
@@ -274,6 +290,7 @@ class CORE_EXPORT QgsTaskManager : public QObject
 
     void taskProgressChanged( double progress );
     void taskStatusChanged( int status );
+    void layersWillBeRemoved( const QStringList& layerIds );
 
   private:
 
@@ -290,6 +307,7 @@ class CORE_EXPORT QgsTaskManager : public QObject
 
     QMap< long, TaskInfo > mTasks;
     QMap< long, QgsTaskList > mTaskDependencies;
+    QMap< long, QStringList > mLayerDependencies;
 
     //! Tracks the next unique task ID
     long mNextTaskId;

tests/src/core/testqgstaskmanager.cpp

@@ -16,6 +16,9 @@
  ***************************************************************************/
 
 #include "qgstaskmanager.h"
+#include "qgsmaplayerregistry.h"
+#include "qgsvectorlayer.h"
+#include "qgsapplication.h"
 #include <QObject>
 #include <QSharedPointer>
 #include <QtTest/QtTest>
@@ -86,19 +89,21 @@ class TestQgsTaskManager : public QObject
     void statusChanged();
     void holdTask();
     void dependancies();
+    void layerDependencies();
 
   private:
 
 };
 
 void TestQgsTaskManager::initTestCase()
 {
-
+  QgsApplication::init();
+  QgsApplication::initQgis();
 }
 
 void TestQgsTaskManager::cleanupTestCase()
 {
-
+  QgsApplication::exitQgis();
 }
 
 void TestQgsTaskManager::init()
@@ -440,6 +445,36 @@ void TestQgsTaskManager::dependancies()
   QCOMPARE( grandChildTask->status(), QgsTask::Terminated );
 }
 
+void TestQgsTaskManager::layerDependencies()
+{
+  //make some layers
+  QgsVectorLayer* layer1 = new QgsVectorLayer( "Point?field=col1:string&field=col2:string&field=col3:string", "layer1", "memory" );
+  QVERIFY( layer1->isValid() );
+  QgsVectorLayer* layer2 = new QgsVectorLayer( "Point?field=col1:string&field=col2:string&field=col3:string", "layer2", "memory" );
+  QVERIFY( layer2->isValid() );
+  QgsVectorLayer* layer3 = new QgsVectorLayer( "Point?field=col1:string&field=col2:string&field=col3:string", "layer3", "memory" );
+  QVERIFY( layer3->isValid() );
+  QgsMapLayerRegistry::instance()->addMapLayers( QList< QgsMapLayer* >() << layer1 << layer2 << layer3 );
+
+  QgsTaskManager manager;
+
+  //test that remove layers cancels all tasks which are dependant on them
+  TestTask* task = new TestTask();
+  task->hold();
+  long taskId = manager.addTask( task );
+  manager.setDependentLayers( taskId, QStringList() << layer2->id() << layer3->id() );
+
+  QCOMPARE( task->status(), QgsTask::OnHold );
+  //removing layer1 should have no effect
+  QgsMapLayerRegistry::instance()->removeMapLayers( QList< QgsMapLayer* >() << layer1 );
+  QCOMPARE( task->status(), QgsTask::OnHold );
+  //removing layer3 should cancel task
+  QgsMapLayerRegistry::instance()->removeMapLayers( QList< QgsMapLayer* >() << layer3 );
+  QCOMPARE( task->status(), QgsTask::Terminated );
+
+  QgsMapLayerRegistry::instance()->removeMapLayers( QList< QgsMapLayer* >() << layer2 );
+}
+
 
 QTEST_MAIN( TestQgsTaskManager )
 #include "testqgstaskmanager.moc"