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refs #581 Use JSON to store timestamps in data cache revision file.

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This commit is contained in:
Mathew Sutcliffe
2016-02-02 18:03:32 +00:00
parent ef38c1620f
commit 97fad301ae
4 changed files with 120 additions and 21 deletions
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23
src/blackmisc/datacache.h
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@@ -42,12 +42,13 @@ namespace BlackMisc
//! RAII class to keep the revision file locked during update.
class LockGuard;
//! Get the state of the disk cache, and prepare to update values.
//! Get the state of the disk cache, and prepare to update any values which are out of date.
//! Return value can be converted to bool, false means update is not started (error, or already up-to-date).
LockGuard beginUpdate();
//! \param timestamps Current in-memory timestamps, to be compared with the on-disk ones.
LockGuard beginUpdate(const QMap<QString, qint64> &timestamps);
//! During update, writes a new revision file.
void writeNewRevision();
//! During update, writes a new revision file with new timestamps.
void writeNewRevision(const QMap<QString, qint64> &timestamps);
//! Release the revision file lock and mark everything up-to-date (called by LockGuard destructor).
void finishUpdate();
@@ -58,6 +59,12 @@ namespace BlackMisc
//! Call before beginUpdate if there is a write pending, so update will start even if there is nothing to read.
void notifyPendingWrite();
//! During update, returns keys which have on-disk timestamps newer than in-memory. Guaranteed not empty.
QSet<QString> keysWithNewerTimestamps() const;
//! During update, returns true if the on-disk timestamp of this key is newer than in-memory.
bool isNewerValueAvailable(const QString &key) const;
private:
mutable QMutex m_mutex { QMutex::Recursive };
bool m_updateInProgress = false;
@@ -66,6 +73,10 @@ namespace BlackMisc
QString m_basename;
QLockFile m_lockFile { m_basename + "/.lock" };
QUuid m_uuid;
QMap<QString, qint64> m_timestamps;
static QJsonObject toJson(const QMap<QString, qint64> &timestamps);
static QMap<QString, qint64> fromJson(const QJsonObject &timestamps);
};
/*!
@@ -81,14 +92,14 @@ namespace BlackMisc
CDataCacheSerializer(CDataCache *owner, const QString &revisionFileName);
//! Save values to persistent store. Called whenever a value is changed locally.
void saveToStore(const BlackMisc::CVariantMap &values, const BlackMisc::CVariantMap &baseline);
void saveToStore(const BlackMisc::CVariantMap &values, const BlackMisc::CValueCachePacket &baseline);
//! 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 defer Whether to defer applying the changes. Used when called by saveToStore.
//! \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);
CDataCacheRevision::LockGuard loadFromStore(const BlackMisc::CValueCachePacket &baseline, bool defer = false);
signals:
//! Signal back to the cache when values have been loaded.