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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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152
src/blackmisc/datacache.cpp
View File

@@ -11,10 +11,33 @@
#include "blackmisc/logmessage.h"
#include "blackmisc/identifier.h"
#include <QStandardPaths>
#include <QLockFile>
namespace BlackMisc
{
class CDataCacheRevision::LockGuard
{
public:
LockGuard(const LockGuard &) = delete;
LockGuard &operator =(const LockGuard &) = delete;
LockGuard(LockGuard &&other) : m_movedFrom(true) { *this = std::move(other); }
LockGuard &operator =(LockGuard &&other) { std::swap(m_movedFrom, other.m_movedFrom); std::swap(m_rev, other.m_rev); return *this; }
~LockGuard()
{
if (! m_movedFrom) { m_rev->finishUpdate(); }
}
operator bool() const { return ! m_movedFrom; }
private:
LockGuard() : m_movedFrom(true) {}
LockGuard(CDataCacheRevision *rev) : m_movedFrom(! rev), m_rev(rev) {}
friend class CDataCacheRevision;
bool m_movedFrom = false;
CDataCacheRevision *m_rev = nullptr;
};
CDataCache::CDataCache() :
CValueCache(CValueCache::Distributed)
{
@@ -109,25 +132,12 @@ namespace BlackMisc
void CDataCacheSerializer::saveToStore(const BlackMisc::CVariantMap &values, const BlackMisc::CVariantMap &baseline)
{
QLockFile revisionFileLock(m_revisionFileName + ".lock");
if (! revisionFileLock.lock())
{
CLogMessage(this).error("Failed to lock %1: %2") << m_revisionFileName << lockFileError(revisionFileLock);
return;
}
loadFromStore(baseline, false, true); // last-minute check for remote changes before clobbering the revision file
m_cache->m_revision.notifyPendingWrite();
auto lock = loadFromStore(baseline, 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());
if (! lock) { return; }
m_cache->m_revision.writeNewRevision();
m_cache->saveToFiles(persistentStore(), values);
if (! m_deferredChanges.isEmpty()) // apply changes which we grabbed at the last minute above
@@ -138,30 +148,11 @@ namespace BlackMisc
}
}
void CDataCacheSerializer::loadFromStore(const BlackMisc::CVariantMap &baseline, bool revLock, bool defer)
CDataCacheRevision::LockGuard CDataCacheSerializer::loadFromStore(const BlackMisc::CVariantMap &baseline, bool defer)
{
QLockFile revisionFileLock(m_revisionFileName + ".lock");
if (revLock && ! revisionFileLock.lock())
auto lock = m_cache->m_revision.beginUpdate();
if (lock && m_cache->m_revision.isPendingRead())
{
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;
CValueCachePacket newValues;
m_cache->loadFromFiles(persistentStore(), baseline, newValues);
m_deferredChanges.insert(newValues);
@@ -173,5 +164,86 @@ namespace BlackMisc
emit valuesLoadedFromStore(m_deferredChanges, CIdentifier::anonymous());
m_deferredChanges.clear();
}
return lock;
}
CDataCacheRevision::LockGuard CDataCacheRevision::beginUpdate()
{
QMutexLocker lock(&m_mutex);
Q_ASSERT(! m_updateInProgress);
Q_ASSERT(! m_lockFile.isLocked());
if (! m_lockFile.lock())
{
CLogMessage(this).error("Failed to lock %1: %2") << m_basename << lockFileError(m_lockFile);
return {};
}
m_updateInProgress = true;
LockGuard guard(this);
QFile revisionFile(m_basename + "/.rev");
if (revisionFile.exists())
{
if (! revisionFile.open(QFile::ReadOnly))
{
CLogMessage(this).error("Failed to open %1: %2") << revisionFile.fileName() << revisionFile.errorString();
return {};
}
QUuid uuid(revisionFile.readAll());
if (uuid == m_uuid)
{
if (m_pendingWrite) { return guard; }
return {};
}
}
m_pendingRead = true;
return guard;
}
void CDataCacheRevision::writeNewRevision()
{
QMutexLocker lock(&m_mutex);
Q_ASSERT(m_updateInProgress);
Q_ASSERT(m_lockFile.isLocked());
QFile revisionFile(m_basename + "/.rev");
if (! revisionFile.open(QFile::WriteOnly))
{
CLogMessage(this).error("Failed to open %1: %2") << revisionFile.fileName() << revisionFile.errorString();
return;
}
m_uuid = CIdentifier().toUuid();
revisionFile.write(m_uuid.toByteArray());
}
void CDataCacheRevision::finishUpdate()
{
QMutexLocker lock(&m_mutex);
Q_ASSERT(m_updateInProgress);
Q_ASSERT(m_lockFile.isLocked());
m_updateInProgress = false;
m_pendingRead = false;
m_pendingWrite = false;
m_lockFile.unlock();
}
bool CDataCacheRevision::isPendingRead() const
{
QMutexLocker lock(&m_mutex);
Q_ASSERT(m_updateInProgress);
return ! m_timestamps.isEmpty();
}
void CDataCacheRevision::notifyPendingWrite()
{
m_pendingWrite = true;
}
}

55
src/blackmisc/datacache.h
View File

@@ -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
};
/*!