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refs #581 Refactor data cache revision file logic into new class CDataCacheRevision.

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This commit is contained in:
Mathew Sutcliffe
2016-02-02 02:17:44 +00:00
parent f9ee637a1e
commit ef38c1620f
2 changed files with 163 additions and 44 deletions
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55
src/blackmisc/datacache.h
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@@ -17,11 +17,57 @@
#include "blackmisc/worker.h"
#include <QUuid>
#include <QFileSystemWatcher>
#include <QLockFile>
namespace BlackMisc
{
class CDataCache;
/*!
* Encapsulates metastate about how the version of the cache in memory compares to the one on disk.
* \threadsafe
*/
class BLACKMISC_EXPORT CDataCacheRevision
{
public:
//! Construct the single instance of the revision metastate.
CDataCacheRevision(const QString &basename) : m_basename(basename) {}
//! Non-copyable.
//! @{
CDataCacheRevision(const CDataCacheRevision &) = delete;
CDataCacheRevision &operator =(const CDataCacheRevision &) = delete;
//! @}
//! RAII class to keep the revision file locked during update.
class LockGuard;
//! Get the state of the disk cache, and prepare to update values.
//! Return value can be converted to bool, false means update is not started (error, or already up-to-date).
LockGuard beginUpdate();
//! During update, writes a new revision file.
void writeNewRevision();
//! Release the revision file lock and mark everything up-to-date (called by LockGuard destructor).
void finishUpdate();
//! True if beginUpdate found some values with timestamps newer than in memory.
bool isPendingRead() const;
//! Call before beginUpdate if there is a write pending, so update will start even if there is nothing to read.
void notifyPendingWrite();
private:
mutable QMutex m_mutex { QMutex::Recursive };
bool m_updateInProgress = false;
bool m_pendingRead = false;
bool m_pendingWrite = false;
QString m_basename;
QLockFile m_lockFile { m_basename + "/.lock" };
QUuid m_uuid;
};
/*!
* Worker which performs (de)serialization on behalf of CDataCache, in a separate thread
* so that the main thread is not blocked by (de)serialization of large objects.
@@ -40,9 +86,9 @@ namespace BlackMisc
//! 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 baseline A snapshot of the currently loaded values, taken when the load is queued.
//! \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(const BlackMisc::CVariantMap &baseline, bool lock = true, bool defer = false);
//! \return Usually ignored, but can be held in order to retain the revision file lock.
CDataCacheRevision::LockGuard loadFromStore(const BlackMisc::CVariantMap &baseline, bool defer = false);
signals:
//! Signal back to the cache when values have been loaded.
@@ -51,7 +97,7 @@ namespace BlackMisc
private:
const QString &persistentStore() const;
const CDataCache *const m_cache = nullptr;
CDataCache *const m_cache = nullptr;
QUuid m_revision;
const QString m_revisionFileName;
BlackMisc::CValueCachePacket m_deferredChanges;
@@ -89,7 +135,8 @@ namespace BlackMisc
const QString m_revisionFileName { persistentStore() + "/.rev" };
CDataCacheSerializer m_serializer { this, m_revisionFileName };
friend class CDataCacheSerializer; // to access protected members of CValueCache
CDataCacheRevision m_revision { persistentStore() + "/" };
friend class CDataCacheSerializer; // to access m_revision and protected members of CValueCache
};
/*!