Add RAII class QgsReadWriteLocker

python/core/auto_generated/qgsreadwritelocker.sip.in

@@ -0,0 +1,68 @@
+/************************************************************************
+ * This file has been generated automatically from                      *
+ *                                                                      *
+ * src/core/qgsreadwritelocker.h                                        *
+ *                                                                      *
+ * Do not edit manually ! Edit header and run scripts/sipify.pl again   *
+ ************************************************************************/
+
+
+
+
+
+class QgsReadWriteLocker
+{
+%Docstring
+The QgsReadWriteLocker class is a convenience class that simplifies locking and unlocking QReadWriteLocks.
+
+Locking and unlocking a QReadWriteLocks in complex functions and statements or in exception handling code
+is error-prone and difficult to debug.
+QgsReadWriteLocker can be used in such situations to ensure that the state of the lock is always well-defined.
+
+QgsReadWriteLocker should be created within a function where a QReadWriteLock needs to be locked.
+The lock may be locked when QgsReadWriteLocker is created or when changeMode is called.
+You can unlock and relock the lock with unlock() and changeMode().
+If locked, the mutex will be unlocked when the QgsReadWriteLocker is destroyed.
+
+.. versionadded:: 3.4
+%End
+
+%TypeHeaderCode
+#include "qgsreadwritelocker.h"
+%End
+  public:
+    enum Mode
+    {
+      Read,
+      Write,
+      Unlocked
+    };
+
+    QgsReadWriteLocker( QReadWriteLock &lock, Mode mode );
+%Docstring
+Create a new QgsReadWriteLocker for ``lock`` and initialize in ``mode``.
+%End
+
+    void changeMode( Mode mode );
+%Docstring
+Change the mode of the lock to ``mode``.
+The lock will be unlocked and relocked as required.
+%End
+
+    void unlock();
+%Docstring
+Unlocks the lock.
+Equivalent to doing ``changeMode( QgsReadWriteLocker.Unlock );``
+%End
+
+    ~QgsReadWriteLocker();
+
+};
+
+/************************************************************************
+ * This file has been generated automatically from                      *
+ *                                                                      *
+ * src/core/qgsreadwritelocker.h                                        *
+ *                                                                      *
+ * Do not edit manually ! Edit header and run scripts/sipify.pl again   *
+ ************************************************************************/

python/core/core_auto.sip

@@ -106,6 +106,7 @@
 %Include auto_generated/qgspythonrunner.sip
 %Include auto_generated/qgsrange.sip
 %Include auto_generated/qgsreadwritecontext.sip
+%Include auto_generated/qgsreadwritelocker.sip
 %Include auto_generated/qgsrenderchecker.sip
 %Include auto_generated/qgsrendercontext.sip
 %Include auto_generated/qgsrulebasedlabeling.sip

src/core/CMakeLists.txt

@@ -280,6 +280,7 @@ SET(QGIS_CORE_SRCS
   qgsproxyprogresstask.cpp
   qgspythonrunner.cpp
   qgsreadwritecontext.cpp
+  qgsreadwritelocker.cpp
   qgsrelation.cpp
   qgsrelationmanager.cpp
   qgsrenderchecker.cpp
@@ -919,6 +920,7 @@ SET(QGIS_CORE_HDRS
   qgspythonrunner.h
   qgsrange.h
   qgsreadwritecontext.h
+  qgsreadwritelocker.h
   qgsrenderchecker.h
   qgsrendercontext.h
   qgsrulebasedlabeling.h

src/core/qgsreadwritelocker.cpp

@@ -0,0 +1,54 @@
+/***************************************************************************
+                         qgsreadwritelocker.cpp
+                         -------------------------
+    begin                : September 2018
+    copyright            : (C) 2018 by Matthias Kuhn
+    email                : matthias@opengis.ch
+ ***************************************************************************/
+
+/***************************************************************************
+ *                                                                         *
+ *   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 "qgsreadwritelocker.h"
+
+QgsReadWriteLocker::QgsReadWriteLocker( QReadWriteLock &lock, QgsReadWriteLocker::Mode mode )
+  : mLock( lock )
+  , mMode( mode )
+{
+  if ( mode == Read )
+    mLock.lockForRead();
+  else if ( mode == Write )
+    mLock.lockForWrite();
+}
+
+void QgsReadWriteLocker::changeMode( QgsReadWriteLocker::Mode mode )
+{
+  if ( mode == mMode )
+    return;
+
+  unlock();
+
+  if ( mMode == Read )
+    mLock.lockForRead();
+  else if ( mMode == Write )
+    mLock.lockForWrite();
+}
+
+void QgsReadWriteLocker::unlock()
+{
+  if ( mMode != Unlocked )
+    mLock.unlock();
+
+  mMode = Unlocked;
+}
+
+QgsReadWriteLocker::~QgsReadWriteLocker()
+{
+  unlock();
+}

src/core/qgsreadwritelocker.h

@@ -0,0 +1,74 @@
+/***************************************************************************
+                         qgsreadwritelocker.cpp
+                         -------------------------
+    begin                : September 2018
+    copyright            : (C) 2018 by Matthias Kuhn
+    email                : matthias@opengis.ch
+ ***************************************************************************/
+
+/***************************************************************************
+ *                                                                         *
+ *   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 QGSREADWRITELOCKER_H
+#define QGSREADWRITELOCKER_H
+
+#include "qgis_core.h"
+
+#include <QReadWriteLock>
+
+/**
+ * \ingroup core
+ * The QgsReadWriteLocker class is a convenience class that simplifies locking and unlocking QReadWriteLocks.
+ *
+ * Locking and unlocking a QReadWriteLocks in complex functions and statements or in exception handling code
+ * is error-prone and difficult to debug.
+ * QgsReadWriteLocker can be used in such situations to ensure that the state of the lock is always well-defined.
+ *
+ * QgsReadWriteLocker should be created within a function where a QReadWriteLock needs to be locked.
+ * The lock may be locked when QgsReadWriteLocker is created or when changeMode is called.
+ * You can unlock and relock the lock with unlock() and changeMode().
+ * If locked, the mutex will be unlocked when the QgsReadWriteLocker is destroyed.
+ *
+ * \since QGIS 3.4
+ */
+class CORE_EXPORT QgsReadWriteLocker
+{
+  public:
+    enum Mode
+    {
+      Read, //!< Lock for read
+      Write, //!< Lock for write
+      Unlocked //!< Unlocked
+    };
+
+    /**
+     * Create a new QgsReadWriteLocker for \a lock and initialize in \a mode.
+     */
+    QgsReadWriteLocker( QReadWriteLock &lock, Mode mode );
+
+    /**
+     * Change the mode of the lock to \a mode.
+     * The lock will be unlocked and relocked as required.
+     */
+    void changeMode( Mode mode );
+
+    /**
+     * Unlocks the lock.
+     * Equivalent to doing ``changeMode( QgsReadWriteLocker::Unlock );``
+     */
+    void unlock();
+
+    ~QgsReadWriteLocker();
+
+  private:
+    QReadWriteLock &mLock;
+    Mode mMode = Unlocked;
+};
+
+#endif // QGSREADWRITELOCKER_H