Query result model threaded fetcher

plus: independent iterators and rewind
qgis · Jan 13, 2021 · 3b7cc24 · 3b7cc24
1 parent f5ffc56
commit 3b7cc24
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Showing 16 changed files with 229 additions and 109 deletions.
diff --git a/python/core/auto_generated/qgsabstractdatabaseproviderconnection.sip.in b/python/core/auto_generated/qgsabstractdatabaseproviderconnection.sip.in
@@ -84,6 +84,11 @@ Returns ``True`` if there are more rows to fetch
         QList<QVariant> nextRow() const;
 %Docstring
 Returns the next result row or an empty row if there are no rows left
+%End
+
+        void rewind();
+%Docstring
+Resets the iterator counter used by :py:func:`~QgsAbstractDatabaseProviderConnection.hasNextRow` and :py:func:`~QgsAbstractDatabaseProviderConnection.nextRow`
 %End
 
         qlonglong fetchedRowCount( ) const;

diff --git a/python/core/auto_generated/qgsqueryresultmodel.sip.in b/python/core/auto_generated/qgsqueryresultmodel.sip.in
@@ -9,6 +9,12 @@
 
 
 
+
+
+
+
+
+
 class QgsQueryResultModel : QAbstractListModel
 {
 %Docstring
@@ -22,11 +28,13 @@ The QgsQueryResultModel class is a model for QgsAbstractDatabaseProviderConnecti
 %End
   public:
 
-    QgsQueryResultModel( const QgsAbstractDatabaseProviderConnection::QueryResult &queryResult, QObject *parent = 0 );
+    QgsQueryResultModel(const QgsAbstractDatabaseProviderConnection::QueryResult& queryResult, QObject *parent = 0 );
 %Docstring
 Constructs a QgsQueryResultModel from a ``queryResult`` with optional ``parent``
 %End
 
+    ~QgsQueryResultModel();
+
   public:
 
     virtual int rowCount( const QModelIndex &parent ) const;
@@ -35,10 +43,10 @@ Constructs a QgsQueryResultModel from a ``queryResult`` with optional ``parent``
 
     virtual QVariant data( const QModelIndex &index, int role ) const;
 
-    virtual void fetchMore( const QModelIndex &parent );
 
-    virtual bool canFetchMore( const QModelIndex &parent ) const;
+  public slots:
 
+    void newRowsReady(int newRowsCount );
 
 };
 

diff --git a/src/core/providers/ogr/qgsgeopackageproviderconnection.cpp b/src/core/providers/ogr/qgsgeopackageproviderconnection.cpp
@@ -425,14 +425,14 @@ QgsAbstractDatabaseProviderConnection::QueryResult QgsGeoPackageProviderConnecti
   return QgsAbstractDatabaseProviderConnection::QueryResult();
 }
 
-QVariantList QgsGeoPackageProviderResultIterator::nextRow()
+QVariantList QgsGeoPackageProviderResultIterator::nextRowPrivate()
 {
   const QVariantList currentRow { mNextRow };
-  mNextRow = nextRowPrivate();
+  mNextRow = nextRowInternal();
   return currentRow;
 }
 
-QVariantList QgsGeoPackageProviderResultIterator::nextRowPrivate()
+QVariantList QgsGeoPackageProviderResultIterator::nextRowInternal()
 {
   QVariantList row;
   if ( mHDS && mOgrLayer )
@@ -457,11 +457,17 @@ QVariantList QgsGeoPackageProviderResultIterator::nextRowPrivate()
         }
       }
     }
+    else
+    {
+      // Release the resources
+      GDALDatasetReleaseResultSet( mHDS.get(), mOgrLayer );
+      mHDS.release();
+    }
   }
   return row;
 }
 
-bool QgsGeoPackageProviderResultIterator::hasNextRow() const
+bool QgsGeoPackageProviderResultIterator::hasNextRowPrivate() const
 {
   return ! mNextRow.isEmpty();
 }
@@ -488,5 +494,8 @@ QList<QgsVectorDataProvider::NativeType> QgsGeoPackageProviderConnection::native
 
 QgsGeoPackageProviderResultIterator::~QgsGeoPackageProviderResultIterator()
 {
-  GDALDatasetReleaseResultSet( mHDS.get(), mOgrLayer );
+  if ( mHDS )
+  {
+    GDALDatasetReleaseResultSet( mHDS.get(), mOgrLayer );
+  }
 }
diff --git a/src/core/providers/ogr/qgsgeopackageproviderconnection.h b/src/core/providers/ogr/qgsgeopackageproviderconnection.h
@@ -34,9 +34,6 @@ struct QgsGeoPackageProviderResultIterator: public QgsAbstractDatabaseProviderCo
 
     ~QgsGeoPackageProviderResultIterator();
 
-    QVariantList nextRow() override;
-    bool hasNextRow() const override;
-
     void setFields( const QgsFields &fields );
 
   private:
@@ -46,7 +43,9 @@ struct QgsGeoPackageProviderResultIterator: public QgsAbstractDatabaseProviderCo
     QgsFields mFields;
     QVariantList mNextRow;
 
-    QVariantList nextRowPrivate();
+    QVariantList nextRowPrivate() override;
+    QVariantList nextRowInternal();
+    bool hasNextRowPrivate() const override;
 
 };
 

diff --git a/src/core/qgsabstractdatabaseproviderconnection.cpp b/src/core/qgsabstractdatabaseproviderconnection.cpp
@@ -446,70 +446,69 @@ QStringList QgsAbstractDatabaseProviderConnection::QueryResult::columns() const
 
 QList<QList<QVariant> > QgsAbstractDatabaseProviderConnection::QueryResult::rows( QgsFeedback* feedback) const
 {
+  if ( ! mResultIterator )
+  {
+    return QList<QList<QVariant> >();
+  }
+
   // mRowCount might be -1 (unknown)
   while ( mResultIterator &&
-          ( mRowCount < 0 || mRows.count() < mRowCount ) &&
-          hasNextRow() && ( ! feedback || ! feedback->isCanceled() ) )
+          mResultIterator->hasNextRow() &&
+          ( ! feedback || ! feedback->isCanceled() ) )
   {
     const QVariantList row( mResultIterator->nextRow() );
     if ( row.isEmpty() )
     {
       break;
     }
-    mRows.push_back( row );
   }
-  return mRows;
+  return mResultIterator->rows();
 }
 
 QList<QVariant> QgsAbstractDatabaseProviderConnection::QueryResult::nextRow() const
 {
-  if ( ! mResultIterator || ! hasNextRow() )
+  if ( ! mResultIterator )
   {
     return QList<QVariant>();
   }
+  return at( mIteratorCounter++ );
+}
 
-  const QList<QVariant> row( mResultIterator->nextRow() );
-
-  if ( ! row.isEmpty() )
-  {
-    mRows.push_back( row );
-  }
-
-  return row;
+void QgsAbstractDatabaseProviderConnection::QueryResult::rewind()
+{
+  mIteratorCounter = 0;
 }
 
 qlonglong QgsAbstractDatabaseProviderConnection::QueryResult::fetchedRowCount() const
 {
-  return mRows.count();
+  if ( ! mResultIterator )
+  {
+    return 0;
+  }
+  return mResultIterator->fetchedRowCount();
 }
 
 QList<QVariant> QgsAbstractDatabaseProviderConnection::QueryResult::at( qlonglong index ) const
 {
-  if ( index < 0 )
+  if ( index < 0 || ! mResultIterator )
   {
     return QList<QVariant>();
   }
 
   // Fetch rows until the index
-  if ( index >= mRows.count( ) )
+  while ( index >= mResultIterator->fetchedRowCount() &&
+          ( mRowCount < 0 || mResultIterator->fetchedRowCount() < mRowCount ) &&
+          mResultIterator->hasNextRow() )
   {
-    while ( mResultIterator && ( mRowCount < 0 || mRows.count() < mRowCount ) && index >= mRows.count() && hasNextRow() )
-    {
-      const QVariantList row { mResultIterator->nextRow() };
-      if ( row.isEmpty() )
-      {
-        break;
-      }
-      mRows.push_back( row );
-    }
+    mResultIterator->nextRow();
   }
 
-  if ( index >= mRows.count( ) )
+  if ( index >= mResultIterator->fetchedRowCount() )
   {
     return QList<QVariant>();
   }
 
-  return mRows.at( index );
+  return mResultIterator->rows().at( index );
 }
 
 
@@ -524,15 +523,9 @@ bool QgsAbstractDatabaseProviderConnection::QueryResult::hasNextRow() const
   {
     return false;
   }
-  const bool results { mResultIterator->hasNextRow() };
-  if ( ! results )
-  {
-    mResultIterator.reset();
-  }
-  return results;
+  return ! at( mIteratorCounter ).isEmpty();
 }
 
-
 void QgsAbstractDatabaseProviderConnection::QueryResult::appendColumn( const QString &columnName )
 {
   mColumns.push_back( columnName );
@@ -548,4 +541,34 @@ QgsAbstractDatabaseProviderConnection::QueryResult::QueryResult( std::shared_ptr
 {}
 
 
+QVariantList QgsAbstractDatabaseProviderConnection::QueryResult::QueryResultIterator::nextRow()
+{
+  QMutexLocker lock(&mMutex);
+  const QVariantList row { nextRowPrivate() };
+  if ( ! row.isEmpty() )
+  {
+    mRows.push_back( row );
+  }
+  return row;
+}
+
+bool QgsAbstractDatabaseProviderConnection::QueryResult::QueryResultIterator::hasNextRow() const
+{
+  QMutexLocker lock(&mMutex);
+  return hasNextRowPrivate();
+}
+
+qlonglong QgsAbstractDatabaseProviderConnection::QueryResult::QueryResultIterator::fetchedRowCount()
+{
+  QMutexLocker lock(&mMutex);
+  return mRows.count();
+}
+
+QList<QList<QVariant> > QgsAbstractDatabaseProviderConnection::QueryResult::QueryResultIterator::rows() const
+{
+  QMutexLocker lock(&mMutex);
+  return mRows;
+}
+
+
 ///@endcond private
diff --git a/src/core/qgsabstractdatabaseproviderconnection.h b/src/core/qgsabstractdatabaseproviderconnection.h
@@ -122,6 +122,11 @@ class CORE_EXPORT QgsAbstractDatabaseProviderConnection : public QgsAbstractProv
          */
         QList<QVariant> nextRow() const;
 
+        /**
+         * Resets the iterator counter used by hasNextRow() and nextRow()
+         */
+        void rewind();
+
         /**
          * Returns the number of fetched rows
          * \see rowCount()
@@ -162,14 +167,26 @@ class CORE_EXPORT QgsAbstractDatabaseProviderConnection : public QgsAbstractProv
 ///@cond private
 
         /**
-         * The QueryResultIterator struct is an abstract interface for provider query results iterators.
+         * The QueryResultIterator struct is an abstract interface for provider query result iterators.
          * Providers must implement their own concrete iterator over query results.
+         *
+         * \note This struct is thread safe.
          */
         struct QueryResultIterator SIP_SKIP
         {
-          virtual QVariantList nextRow() = 0;
-          virtual bool hasNextRow() const = 0;
+          QVariantList nextRow();
+          bool hasNextRow() const;
+          qlonglong fetchedRowCount();
           virtual ~QueryResultIterator() = default;
+          QList<QList<QVariant> > rows() const;
+
+      private:
+
+          virtual QVariantList nextRowPrivate() = 0;
+          virtual bool hasNextRowPrivate() const = 0;
+          mutable QList<QList<QVariant>> mRows;
+          mutable QMutex mMutex;
+
         };
 
         /**
@@ -202,8 +219,8 @@ class CORE_EXPORT QgsAbstractDatabaseProviderConnection : public QgsAbstractProv
 
         mutable std::shared_ptr<QueryResultIterator> mResultIterator;
         QStringList mColumns;
-        mutable QList<QList<QVariant>> mRows;
         qlonglong mRowCount = 0;
+        mutable qlonglong mIteratorCounter = 0;
 
     };
 

diff --git a/src/core/qgsqueryresultmodel.cpp b/src/core/qgsqueryresultmodel.cpp
@@ -25,12 +25,12 @@ QgsQueryResultModel::QgsQueryResultModel(const QgsAbstractDatabaseProviderConnec
 {
   if ( mQueryResult.hasNextRow() )
   {
-    ResultWorker *worker = new ResultWorker( &mQueryResult );
-    worker->moveToThread(&mWorkerThread);
-    //connect(&mWorkerThread, &QThread::finished, worker, &ResultWorker::stopFetching );
-    connect(&mWorkerThread, &QThread::finished, worker, &QObject::deleteLater);
-    connect(&mWorkerThread, &QThread::started, worker, &ResultWorker::fetchRows);
-    connect(worker, &ResultWorker::rowsReady, this, &QgsQueryResultModel::newRowsReady );
+    mWorker = new ResultWorker( &mQueryResult );
+    mWorker->moveToThread(&mWorkerThread);
+    connect(&mWorkerThread, &QThread::finished, mWorker, &ResultWorker::stopFetching );
+    connect(&mWorkerThread, &QThread::finished, mWorker, &QObject::deleteLater);
+    connect(&mWorkerThread, &QThread::started, mWorker, &ResultWorker::fetchRows);
+    connect(mWorker, &ResultWorker::rowsReady, this, &QgsQueryResultModel::newRowsReady );
     mWorkerThread.start();
   }
 }
@@ -44,8 +44,12 @@ void QgsQueryResultModel::newRowsReady( int newRowCount )
 
 QgsQueryResultModel::~QgsQueryResultModel()
 {
-  mWorkerThread.quit();
-  mWorkerThread.wait();
+  if ( mWorker )
+  {
+    mWorker->stopFetching();
+    mWorkerThread.quit();
+    mWorkerThread.wait();
+  }
 }
 
 int QgsQueryResultModel::rowCount( const QModelIndex &parent ) const
@@ -81,26 +85,27 @@ QVariant QgsQueryResultModel::data( const QModelIndex &index, int role ) const
 
 void ResultWorker::fetchRows()
 {
-  int rowCount = 0;
-  while ( mQueryResult->hasNextRow() && mStopFetching == 0 )
+  qlonglong rowCount { 0 };
+  while ( mStopFetching == 0 )
   {
-     mQueryResult->nextRow();
-     ++rowCount;
-     if ( rowCount == ROWS_TO_FETCH && mStopFetching == 0 )
-     {
-       emit rowsReady( rowCount );
-       rowCount = 0;
-     }
+    if ( mQueryResult->at( rowCount ).isEmpty() )
+    {
+      break;
+    }
+    ++rowCount;
+    if ( rowCount % ROWS_TO_FETCH == 0 && mStopFetching == 0 )
+    {
+       emit rowsReady( ROWS_TO_FETCH );
+    }
   }
 
-  if ( rowCount  > 0 && mStopFetching == 0 )
+  if ( rowCount % ROWS_TO_FETCH && mStopFetching == 0 )
   {
-    emit rowsReady( rowCount );
+    emit rowsReady( rowCount % ROWS_TO_FETCH );
   }
 }
 
 void ResultWorker::stopFetching()
 {
-  qDebug() << "Stop fetching" << mQueryResult->fetchedRowCount();
   mStopFetching = 1;
 }