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

src/blackcore/datacache.cpp

@@ -0,0 +1,129 @@
+/* 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.
+ */
+
+#include "datacache.h"
+#include "blackmisc/logmessage.h"
+#include "blackmisc/identifier.h"
+#include <QStandardPaths>
+
+using namespace BlackMisc;
+
+namespace BlackCore
+{
+
+    CDataCache::CDataCache() :
+        CValueCache(CValueCache::Distributed)
+    {
+        if (! QDir::root().mkpath(persistentStore()))
+        {
+            CLogMessage(this).error("Failed to create directory %1") << persistentStore();
+        }
+
+        connect(this, &CValueCache::valuesChangedByLocal, this, &CDataCache::saveToStore);
+
+        connect(&m_reloadTimer, &QTimer::timeout, this, [this]() { loadFromStore(); });
+        m_reloadTimer.start(1000);
+        loadFromStore();
+    }
+
+    CDataCache *CDataCache::instance()
+    {
+        static CDataCache cache;
+        return &cache;
+    }
+
+    const QString &CDataCache::persistentStore()
+    {
+        static const QString dir = QStandardPaths::writableLocation(QStandardPaths::GenericDataLocation) + "/org.swift-project/data/cache/core";
+        return dir;
+    }
+
+    QString lockFileError(const QLockFile &lock)
+    {
+        switch (lock.error())
+        {
+        case QLockFile::NoError: return "No error";
+        case QLockFile::PermissionError: return "Insufficient permission";
+        case QLockFile::UnknownError: return "Unknown filesystem error";
+        case QLockFile::LockFailedError:
+        {
+            QString hostname, appname;
+            qint64 pid = 0;
+            lock.getLockInfo(&pid, &hostname, &appname);
+            return QString("Lock open in another process (%1 %2 on %3)").arg(hostname, QString::number(pid), appname);
+        }
+        default: return "Bad error number";
+        }
+    }
+
+    void CDataCache::saveToStore(const BlackMisc::CVariantMap &values)
+    {
+        QMutexLocker lock(&m_mutex);
+
+        QLockFile revisionFileLock(m_revisionFileName);
+        if (! revisionFileLock.lock())
+        {
+            CLogMessage(this).error("Failed to lock %1: %2") << m_revisionFileName << lockFileError(revisionFileLock);
+            return;
+        }
+
+        loadFromStore(false, true); // last-minute check for remote changes before clobbering the revision file
+        for (const auto &key : values.keys()) { m_deferredChanges.remove(key); } // ignore changes that we are about to overwrite
+
+        QFile revisionFile(m_revisionFileName);
+        if (! revisionFile.open(QFile::WriteOnly))
+        {
+            CLogMessage(this).error("Failed to open %1: %2") << m_revisionFileName << revisionFile.errorString();
+            return;
+        }
+        m_revision = CIdentifier().toUuid();
+        revisionFile.write(m_revision.toByteArray());
+
+        saveToFiles(persistentStore(), values);
+    }
+
+    void CDataCache::loadFromStore(bool revLock, bool defer)
+    {
+        QMutexLocker lock(&m_mutex);
+
+        QLockFile revisionFileLock(m_revisionFileName);
+        if (revLock && ! revisionFileLock.lock())
+        {
+            CLogMessage(this).error("Failed to lock %1: %2") << m_revisionFileName << lockFileError(revisionFileLock);
+            return;
+        }
+
+        QFile revisionFile(m_revisionFileName);
+        if (! revisionFile.exists())
+        {
+            return;
+        }
+        if (! revisionFile.open(QFile::ReadOnly))
+        {
+            CLogMessage(this).error("Failed to open %1: %2") << m_revisionFileName << revisionFile.errorString();
+            return;
+        }
+
+        QUuid newRevision(revisionFile.readAll());
+        if (m_revision != newRevision)
+        {
+            m_revision = newRevision;
+            CVariantMap newValues;
+            loadFromFiles(persistentStore(), newValues);
+            m_deferredChanges.insert(newValues);
+        }
+
+        if (! (m_deferredChanges.isEmpty() || defer))
+        {
+            changeValuesFromRemote(m_deferredChanges, CIdentifier::anonymous());
+            m_deferredChanges.clear();
+        }
+    }
+
+}

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