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refs #581, #592 Make sure syncLoad checks if the next load would load the value, if it is not currently loading.

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This commit is contained in:
Mathew Sutcliffe
2016-02-06 18:40:31 +00:00
parent 5a0db69415
commit a58dddfa19
3 changed files with 16 additions and 11 deletions
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16
src/blackmisc/datacache.cpp
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@@ -86,12 +86,12 @@ namespace BlackMisc
std::future<CVariant> CDataCache::syncLoad(QObject *pageOwner, const QString &key)
{
auto future = m_revision.promiseLoadedValue(pageOwner, key);
auto future = m_revision.promiseLoadedValue(pageOwner, key, getTimestampSync(key));
if (future.valid())
{
return future;
}
else // value is not currently loading, so immediately return the current value
else // value is not awaiting load, so immediately return the current value
{
std::promise<CVariant> p;
p.set_value(getValueSync(key));
@@ -217,7 +217,7 @@ namespace BlackMisc
});
}
CDataCacheRevision::LockGuard CDataCacheRevision::beginUpdate(const QMap<QString, qint64> &timestamps)
CDataCacheRevision::LockGuard CDataCacheRevision::beginUpdate(const QMap<QString, qint64> &timestamps, bool updateUuid)
{
QMutexLocker lock(&m_mutex);
@@ -253,7 +253,7 @@ namespace BlackMisc
if (m_pendingWrite) { return guard; }
return {};
}
m_uuid = uuid;
if (updateUuid) { m_uuid = uuid; }
auto timesToLive = fromJson(json.value("ttl").toObject());
auto newTimestamps = fromJson(json.value("timestamps").toObject());
@@ -348,18 +348,18 @@ namespace BlackMisc
return QSet<QString>::fromList(m_timestamps.keys());
}
bool CDataCacheRevision::isNewerValueAvailable(const QString &key) const
bool CDataCacheRevision::isNewerValueAvailable(const QString &key, qint64 timestamp)
{
QMutexLocker lock(&m_mutex);
return m_updateInProgress && m_timestamps.contains(key);
return (m_updateInProgress || beginUpdate({{ key, timestamp }}, false)) && m_timestamps.contains(key);
}
std::future<CVariant> CDataCacheRevision::promiseLoadedValue(QObject *pageOwner, const QString &key)
std::future<CVariant> CDataCacheRevision::promiseLoadedValue(QObject *pageOwner, const QString &key, qint64 currentTimestamp)
{
QMutexLocker lock(&m_mutex);
if (isNewerValueAvailable(key))
if (isNewerValueAvailable(key, currentTimestamp))
{
std::promise<CVariant> promise;
auto future = promise.get_future();

7
src/blackmisc/datacache.h
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@@ -46,7 +46,8 @@ namespace BlackMisc
//! 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).
//! \param timestamps Current in-memory timestamps, to be compared with the on-disk ones.
LockGuard beginUpdate(const QMap<QString, qint64> &timestamps);
//! \param updateUuid Whether to prepare for an actual update, or just interrograte whether one is needed.
LockGuard beginUpdate(const QMap<QString, qint64> &timestamps, bool updateUuid = true);
//! During update, writes a new revision file with new timestamps.
void writeNewRevision(const QMap<QString, qint64> &timestamps);
@@ -64,10 +65,10 @@ namespace BlackMisc
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;
bool isNewerValueAvailable(const QString &key, qint64 timestamp);
//! Return a future which will be made ready when the value is loaded. Future is invalid if value is not loading.
std::future<CVariant> promiseLoadedValue(QObject *pageOwner, const QString &key);
std::future<CVariant> promiseLoadedValue(QObject *pageOwner, const QString &key, qint64 currentTimestamp);
//! Returns (by move) the container of promises to load values.
std::vector<std::tuple<QObject *, QString, std::promise<CVariant>>> loadedValuePromises();

4
src/blackmisc/valuecache.h
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@@ -229,6 +229,10 @@ namespace BlackMisc
//! \threadsafe
CVariant getValueSync(const QString &key) { return std::get<0>(getValue(key)); }
//! Synchronously return a current timestamp.
//! \threadsafe
qint64 getTimestampSync(const QString &key) { return std::get<1>(getValue(key)); }
private:
friend class Private::CValuePage;
struct Element;