refs #460 CDataCache for dynamic (downloaded/generated) data with file-based distribution among processes.

src/blackcore/datacache.h

@@ -0,0 +1,110 @@
+/* Copyright (C) 2015
+ * swift project Community / Contributors
+ *
+ * This file is part of swift project. It is subject to the license terms in the LICENSE file found in the top-level
+ * directory of this distribution and at http://www.swift-project.org/license.html. No part of swift project,
+ * including this file, may be copied, modified, propagated, or distributed except according to the terms
+ * contained in the LICENSE file.
+ */
+
+//! \file
+
+#ifndef BLACKCORE_DATACACHE_H
+#define BLACKCORE_DATACACHE_H
+
+#include "blackcore/blackcoreexport.h"
+#include "blackmisc/valuecache.h"
+
+namespace BlackCore
+{
+
+    /*!
+     * Singleton derived class of CValueCache, for core dynamic data.
+     *
+     * File-based distribution between processes is built-in to the class.
+     */
+    class BLACKCORE_EXPORT CDataCache : public BlackMisc::CValueCache
+    {
+    public:
+        //! Return the singleton instance.
+        static CDataCache *instance();
+
+        //! The directory where core data are stored.
+        static const QString &persistentStore();
+
+    private:
+        CDataCache();
+
+        //! Save values to persistent store. Called whenever a value is changed locally.
+        void saveToStore(const BlackMisc::CVariantMap &values);
+
+        //! Load values from persistent store. Called once per second.
+        //! Also called by saveToStore, to ensure that remote changes to unrelated values are not lost.
+        //! \param lock Whether to acquire the revision file lock. Used when called by saveToStore.
+        //! \param defer Whether to defer applying the changes. Used when called by saveToStore.
+        void loadFromStore(bool lock = true, bool defer = false);
+
+        QTimer m_reloadTimer;
+        QUuid m_revision;
+        const QString m_revisionFileName { persistentStore() + "/.rev" };
+        BlackMisc::CVariantMap m_deferredChanges;
+    };
+
+    /*!
+     * Class template for accessing a specific value in the CDataCache.
+     * \tparam Trait A subclass of BlackCore::CDataTrait that identifies the value's key and other metadata.
+     */
+    template <typename Trait>
+    class CData : public BlackMisc::CCached<typename Trait::type>
+    {
+    public:
+        //! \copydoc BlackMisc::CCached::NotifySlot
+        template <typename T>
+        using NotifySlot = typename BlackMisc::CCached<typename Trait::type>::template NotifySlot<T>;
+
+        //! Constructor.
+        //! \param owner Will be the parent of the internal QObject used to access the value.
+        //! \param slot Slot to call when the value is modified by another object.
+        //!             Must be a void, non-const member function of the owner.
+        template <typename T>
+        CData(T *owner, NotifySlot<T> slot = nullptr) :
+            CData::CCached(CDataCache::instance(), Trait::key(), Trait::isValid, Trait::defaultValue(), owner, slot)
+        {}
+
+        //! Reset the data to its default value.
+        void setDefault() { this->set(Trait::defaultValue()); }
+    };
+
+    /*!
+     * Base class for traits to be used as template argument to BlackCore::CData.
+     */
+    template <typename T>
+    struct CDataTrait
+    {
+        //! Data type of the value.
+        using type = T;
+
+        //! Key string of the value. Reimplemented in derived class.
+        static const char *key() { qFatal("Not implemented"); return ""; }
+
+        //! Validator function. Return true if the argument is valid, false otherwise. Default
+        //! implementation just returns true. Reimplemented in derived class to support validation of the value.
+        static bool isValid(const T &) { return true; }
+
+        //! Return the value to use in case the supplied value does not satisfy the validator.
+        //! Default implementation returns a default-constructed value.
+        static const T &defaultValue() { static const T def {}; return def; }
+
+        //! Deleted default constructor.
+        CDataTrait() = delete;
+
+        //! Deleted copy constructor.
+        CDataTrait(const CDataTrait &) = delete;
+
+        //! Deleted copy assignment operator.
+        CDataTrait &operator =(const CDataTrait &) = delete;
+    };
+
+}
+
+#endif