Add a QgsTask subclass for proxying progress reports from a

blocking operation via task manager

Allows use of the task manager progress reporting system from
operations which are blocking (and cannot be made background
tasks!), e.g. layout exporting, project loading.

python/core/auto_generated/qgsproxyprogresstask.sip.in

@@ -0,0 +1,61 @@
+/************************************************************************
+ * This file has been generated automatically from                      *
+ *                                                                      *
+ * src/core/qgsproxyprogresstask.h                                      *
+ *                                                                      *
+ * Do not edit manually ! Edit header and run scripts/sipify.pl again   *
+ ************************************************************************/
+
+
+
+
+class QgsProxyProgressTask : QgsTask
+{
+%Docstring
+
+A QgsTask shell which proxies progress reports.
+
+Simple task shell which runs until finalized and reports progress only.
+This is usually used to expose a blocking operation's progress via
+task manager.
+
+.. versionadded:: 3.4
+%End
+
+%TypeHeaderCode
+#include "qgsproxyprogresstask.h"
+%End
+  public:
+
+    QgsProxyProgressTask( const QString &description );
+%Docstring
+Constructor for QgsProxyProgressTask, with the specified ``description``.
+%End
+
+    void finalize( bool result );
+%Docstring
+Finalizes the task, with the specified ``result``.
+
+This should be called when the operation being proxied has completed,
+to remove this proxy task from the task manager.
+%End
+
+    virtual bool run();
+
+
+    void setProxyProgress( double progress );
+%Docstring
+Sets the ``progress`` (from 0 to 100) for the proxied operation.
+
+This method is safe to call from the main thread.
+%End
+
+};
+
+/************************************************************************
+ * This file has been generated automatically from                      *
+ *                                                                      *
+ * src/core/qgsproxyprogresstask.h                                      *
+ *                                                                      *
+ * Do not edit manually ! Edit header and run scripts/sipify.pl again   *
+ ************************************************************************/

python/core/core_auto.sip

@@ -348,6 +348,7 @@
 %Include auto_generated/qgspluginlayer.sip
 %Include auto_generated/qgspointxy.sip
 %Include auto_generated/qgsproject.sip
+%Include auto_generated/qgsproxyprogresstask.sip
 %Include auto_generated/qgsrelationmanager.sip
 %Include auto_generated/qgsrelation.sip
 %Include auto_generated/qgsrunprocess.sip

src/core/CMakeLists.txt

@@ -276,6 +276,7 @@ SET(QGIS_CORE_SRCS
   qgspropertytransformer.cpp
   qgsprovidermetadata.cpp
   qgsproviderregistry.cpp
+  qgsproxyprogresstask.cpp
   qgspythonrunner.cpp
   qgsreadwritecontext.cpp
   qgsrelation.cpp
@@ -627,6 +628,7 @@ SET(QGIS_CORE_MOC_HDRS
   qgspointxy.h
   qgspointlocator.h
   qgsproject.h
+  qgsproxyprogresstask.h
   qgsrelationmanager.h
   qgsrelation.h
   qgsrunprocess.h

src/core/qgsproxyprogresstask.cpp

@@ -0,0 +1,43 @@
+/***************************************************************************
+                             qgsproxyprogresstask.cpp
+                             ------------------------
+    begin                : August 2018
+    copyright            : (C) 2018 by Nyall Dawson
+    email                : nyall dot dawson at gmail dot com
+ ***************************************************************************/
+
+/***************************************************************************
+ *                                                                         *
+ *   This program is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU General Public License as published by  *
+ *   the Free Software Foundation; either version 2 of the License, or     *
+ *   (at your option) any later version.                                   *
+ *                                                                         *
+ ***************************************************************************/
+
+#include "qgsproxyprogresstask.h"
+
+QgsProxyProgressTask::QgsProxyProgressTask( const QString &description )
+  : QgsTask( description, QgsTask::Flags() )
+{
+}
+
+void QgsProxyProgressTask::finalize( bool result )
+{
+  mResult = result;
+  mNotFinishedWaitCondition.wakeAll();
+}
+
+bool QgsProxyProgressTask::run()
+{
+  mNotFinishedMutex.lock();
+  mNotFinishedWaitCondition.wait( &mNotFinishedMutex );
+  mNotFinishedMutex.unlock();
+
+  return mResult;
+}
+
+void QgsProxyProgressTask::setProxyProgress( double progress )
+{
+  QMetaObject::invokeMethod( this, "setProgress", Qt::AutoConnection, Q_ARG( double, progress ) );
+}

src/core/qgsproxyprogresstask.h

@@ -0,0 +1,72 @@
+/***************************************************************************
+                             qgsproxyprogresstask.h
+                             ----------------------
+    begin                : August 2018
+    copyright            : (C) 2018 by Nyall Dawson
+    email                : nyall dot dawson at gmail dot com
+ ***************************************************************************/
+
+/***************************************************************************
+ *                                                                         *
+ *   This program is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU General Public License as published by  *
+ *   the Free Software Foundation; either version 2 of the License, or     *
+ *   (at your option) any later version.                                   *
+ *                                                                         *
+ ***************************************************************************/
+
+#ifndef QGSPROXYPROGRESSTASK_H
+#define QGSPROXYPROGRESSTASK_H
+
+#include "qgsvectorlayer.h"
+#include "qgsvirtuallayerdefinition.h"
+#include "qgstaskmanager.h"
+
+/**
+ * \ingroup core
+ *
+ * A QgsTask shell which proxies progress reports.
+ *
+ * Simple task shell which runs until finalized and reports progress only.
+ * This is usually used to expose a blocking operation's progress via
+ * task manager.
+ *
+ * \since QGIS 3.4
+ */
+class CORE_EXPORT QgsProxyProgressTask : public QgsTask
+{
+    Q_OBJECT
+
+  public:
+
+    /**
+     * Constructor for QgsProxyProgressTask, with the specified \a description.
+     */
+    QgsProxyProgressTask( const QString &description );
+
+    /**
+     * Finalizes the task, with the specified \a result.
+     *
+     * This should be called when the operation being proxied has completed,
+     * to remove this proxy task from the task manager.
+     */
+    void finalize( bool result );
+
+    bool run() override;
+
+    /**
+     * Sets the \a progress (from 0 to 100) for the proxied operation.
+     *
+     * This method is safe to call from the main thread.
+     */
+    void setProxyProgress( double progress );
+
+  private:
+
+    QWaitCondition mNotFinishedWaitCondition;
+    QMutex mNotFinishedMutex;
+    bool mResult = true;
+
+};
+
+#endif // QGSPROXYPROGRESSTASK_H