datacache.cpp

// SPDX-FileCopyrightText: Copyright (C) 2015 swift Project Community / Contributors
// SPDX-License-Identifier: GPL-3.0-or-later OR LicenseRef-swift-pilot-client-1

 
#include "misc/datacache.h"
 
#include <chrono>
#include <memory>
#include <utility>
 
#include <QByteArray>
#include <QDir>
#include <QFile>
#include <QFlags>
#include <QIODevice>
#include <QJsonDocument>
#include <QJsonValue>
#include <QMutexLocker>
#include <QStandardPaths>
#include <QTimer>
#include <Qt>
 
#include "misc/atomicfile.h"
#include "misc/identifier.h"
#include "misc/logmessage.h"
#include "misc/processinfo.h"
 
namespace swift::misc
{
 
    using private_ns::CValuePage;
    using private_ns::CDataPageQueue;
 
    class CDataCacheRevision::LockGuard
    {
    public:
        LockGuard(const LockGuard &) = delete;
        LockGuard &operator=(const LockGuard &) = delete;
        LockGuard(LockGuard &&other) noexcept : m_movedFrom(true) { *this = std::move(other); }
        LockGuard &operator=(LockGuard &&other) noexcept
        {
            auto tuple = std::tie(other.m_movedFrom, other.m_keepPromises, other.m_rev);
            std::tie(m_movedFrom, m_keepPromises, m_rev).swap(tuple);
            return *this;
        }
 
        ~LockGuard()
        {
            if (!m_movedFrom)
            {
                m_rev->finishUpdate(m_keepPromises);
            }
        }
 
        operator bool() const { return !m_movedFrom; }
 
    private:
        LockGuard() : m_movedFrom(true) {}
        LockGuard(CDataCacheRevision *rev) : m_movedFrom(!rev), m_rev(rev) {}
        LockGuard &keepPromises()
        {
            m_keepPromises = true;
            return *this;
        }
        friend class CDataCacheRevision;
 
        bool m_movedFrom = false;
        bool m_keepPromises = false;
        CDataCacheRevision *m_rev = nullptr;
    };
 
    CDataCache::CDataCache() : CValueCache(1), m_serializer(new CDataCacheSerializer { this, revisionFileName() })
    {
        if (!QDir::root().mkpath(persistentStore()))
        {
            CLogMessage(this).error(u"Failed to create directory '%1'") << persistentStore();
        }
 
        connect(this, &CValueCache::valuesChangedByLocal, this, &CDataCache::saveToStoreAsync);
        connect(this, &CValueCache::valuesChangedByLocal, this, [=, this](CValueCachePacket values) {
            values.setSaved();
            changeValuesFromRemote(values, CIdentifier());
        });
        connect(&m_watcher, &QFileSystemWatcher::fileChanged, this, &CDataCache::loadFromStoreAsync);
        connect(m_serializer, &CDataCacheSerializer::valuesLoadedFromStore, this, &CDataCache::changeValuesFromRemote,
                Qt::DirectConnection);
 
        if (!QFile::exists(revisionFileName()))
        {
            const bool res = QFile(revisionFileName()).open(QFile::WriteOnly);
            SWIFT_VERIFY_X(res, Q_FUNC_INFO, "Could not open revision file");
        }
        m_serializer->loadFromStore({}, false, true); // load pinned values
        singleShot(0, this,
                   [this] // only start the serializer if the main thread event loop runs
                   {
                       m_serializer->start();
                       m_watcher.addPath(revisionFileName());
                       loadFromStoreAsync();
                   });
    }
 
    CDataCache::~CDataCache() { m_serializer->quitAndWait(); }
 
    CDataCache *CDataCache::instance()
    {
        static std::unique_ptr<CDataCache> cache(new CDataCache);
        static auto dummy = (connect(qApp, &QObject::destroyed, cache.get(), [] { cache.reset(); }), nullptr);
        Q_UNUSED(dummy) // declared as static to get thread-safe initialization
        return cache.get();
    }
 
    const QString &CDataCache::persistentStore()
    {
        static const QString dir = CFileUtils::appendFilePaths(getCacheRootDirectory(), relativeFilePath());
        return dir;
    }
 
    const QString &CDataCache::revisionFileName()
    {
        static const QString rev = CFileUtils::appendFilePaths(persistentStore(), ".rev");
        return rev;
    }
 
    QString CDataCache::filenameForKey(const QString &key)
    {
        return CFileUtils::appendFilePaths(persistentStore(), instance()->CValueCache::filenameForKey(key));
    }
 
    QStringList CDataCache::enumerateStore() const { return enumerateFiles(persistentStore()); }
 
    bool CDataCache::synchronize(const QString &key)
    {
        constexpr auto timeout = std::chrono::seconds(1);
        constexpr auto ready = std::future_status::ready;
        constexpr auto zero = std::chrono::seconds::zero();
 
        std::future<void> future = m_revision.promiseLoadedValue(key, getTimestampSync(key));
        if (future.valid())
        {
            std::future_status s {};
            do
            {
                s = future.wait_for(timeout);
            }
            while (s != ready && m_revision.isNewerValueAvailable(key, getTimestampSync(key)));
            if (s != ready)
            {
                s = future.wait_for(zero);
            }
            if (s != ready)
            {
                return false;
            }

            //  maybe this happens if a cache is written and this takes a while, maybe we can
            //  use a write in prgress flag or such?
            try
            {
                future.get();
            }
            catch (const std::future_error &)
            {
                return false;
            } // broken promise
            return true;
        }
        return false;
    }
 
    void CDataCache::setTimeToLive(const QString &key, int ttl)
    {
        singleShot(0, m_serializer, [this, key, ttl] { m_revision.setTimeToLive(key, ttl); });
    }
 
    void CDataCache::renewTimestamp(const QString &key, qint64 timestamp)
    {
        singleShot(0, m_serializer, [this, key, timestamp] { m_revision.overrideTimestamp(key, timestamp); });
    }
 
    qint64 CDataCache::getTimestampOnDisk(const QString &key) { return m_revision.getTimestampOnDisk(key); }
 
    void CDataCache::pinValue(const QString &key)
    {
        singleShot(0, m_serializer, [this, key] { m_revision.pinValue(key); });
    }
 
    void CDataCache::deferValue(const QString &key)
    {
        singleShot(0, m_serializer, [this, key] { m_revision.deferValue(key); });
    }
 
    void CDataCache::admitValue(const QString &key, bool triggerLoad)
    {
        m_revision.admitValue(key);
        if (triggerLoad)
        {
            loadFromStoreAsync();
        }
    }
 
    void CDataCache::sessionValue(const QString &key)
    {
        singleShot(0, m_serializer, [this, key] { m_revision.sessionValue(key); });
    }
 
    const QString &CDataCache::relativeFilePath()
    {
        static const QString p("/data/cache/core");
        return p;
    }
 
    void CDataCache::saveToStoreAsync(const swift::misc::CValueCachePacket &values)
    {
        singleShot(0, m_serializer,
                   [this, values] { m_serializer->saveToStore(values.toVariantMap(), getAllValuesWithTimestamps()); });
    }
 
    void CDataCache::loadFromStoreAsync()
    {
        singleShot(0, m_serializer, [this] { m_serializer->loadFromStore(getAllValuesWithTimestamps()); });
    }
 
    void CDataCache::connectPage(CValuePage *page)
    {
        auto *queue = new CDataPageQueue(page);
        connect(page, &CValuePage::valuesWantToCache, this, &CDataCache::changeValues);
        connect(this, &CDataCache::valuesChanged, queue, &CDataPageQueue::queueValuesFromCache, Qt::DirectConnection);
    }
 
    void CDataPageQueue::queueValuesFromCache(const CValueCachePacket &values, QObject *changedBy)
    {
        QMutexLocker lock(&m_mutex);
        if (m_queue.isEmpty())
        {
            singleShot(0, this, [this] { setQueuedValuesFromCache(); });
        }
        m_queue.push_back(std::make_pair(values, changedBy));
    }
 
    void CDataPageQueue::setQueuedValuesFromCache()
    {
        QMutexLocker lock(&m_mutex);
        decltype(m_queue) queue;
        std::swap(m_queue, queue);
        lock.unlock();
 
        for (const auto &pair : std::as_const(queue))
        {
            m_page->setValuesFromCache(pair.first, pair.second);
        }
    }
 
    void CDataPageQueue::setQueuedValueFromCache(const QString &key)
    {
        QMutexLocker lock(&m_mutex);
 
        decltype(m_queue) filtered;
        for (auto &pair : m_queue)
        {
            if (pair.first.contains(key))
            {
                filtered.push_back({ pair.first.takeByKey(key), pair.second });
            }
        }
        lock.unlock();
        for (const auto &pair : filtered)
        {
            m_page->setValuesFromCache(pair.first, pair.second);
        }
    }
 
    const QStringList &CDataCacheSerializer::getLogCategories()
    {
        static const QStringList cats { swift::misc::CLogCategories::cache() };
        return cats;
    }
 
    CDataCacheSerializer::CDataCacheSerializer(CDataCache *owner, const QString &revisionFileName)
        : CContinuousWorker(owner, QStringLiteral("CDataCacheSerializer '%1'").arg(revisionFileName)), m_cache(owner),
          m_revisionFileName(revisionFileName)
    {}
 
    const QString &CDataCacheSerializer::persistentStore() const { return CDataCache::persistentStore(); }
 
    void CDataCacheSerializer::saveToStore(const swift::misc::CVariantMap &values,
                                           const swift::misc::CValueCachePacket &baseline)
    {
        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
 
        if (!lock)
        {
            return;
        }
        m_cache->m_revision.writeNewRevision(baseline.toTimestampMap());
 
        auto msg = m_cache->saveToFiles(persistentStore(), values, baseline.toTimestampMapString(values.keys()));
        msg.setCategories(this);
        CLogMessage::preformatted(msg);
 
        applyDeferredChanges(); // apply changes which we grabbed at the last minute above
    }
 
    CDataCacheRevision::LockGuard CDataCacheSerializer::loadFromStore(const CValueCachePacket &baseline, bool defer,
                                                                      bool pinsOnly)
    {
        auto lock = m_cache->m_revision.beginUpdate(baseline.toTimestampMap(), !pinsOnly, pinsOnly);
        if (lock && m_cache->m_revision.isPendingRead())
        {
            CValueCachePacket newValues;
            if (!m_cache->m_revision.isFound())
            {
                m_cache->loadFromFiles(persistentStore(), {}, {}, newValues, {}, true);
                m_cache->m_revision.regenerate(newValues);
                newValues.clear();
            }
            auto msg =
                m_cache->loadFromFiles(persistentStore(), m_cache->m_revision.keysWithNewerTimestamps(),
                                       baseline.toVariantMap(), newValues, m_cache->m_revision.timestampsAsString());
            newValues.setTimestamps(m_cache->m_revision.newerTimestamps());
 
            auto missingKeys = m_cache->m_revision.keysWithNewerTimestamps() - newValues.keys();
            if (!missingKeys.isEmpty())
            {
                m_cache->m_revision.writeNewRevision({}, missingKeys);
            }
 
            msg.setCategories(this);
            CLogMessage::preformatted(msg);
            m_deferredChanges.insert(newValues);
        }
 
        if (!defer)
        {
            applyDeferredChanges();
        }
        return lock;
    }
 
    void CDataCacheSerializer::applyDeferredChanges()
    {
        if (!m_deferredChanges.isEmpty())
        {
            m_deferredChanges.setSaved();
            emit valuesLoadedFromStore(m_deferredChanges, CIdentifier::null());
            deliverPromises(m_cache->m_revision.loadedValuePromises());
            m_deferredChanges.clear();
        }
    }
 
    void CDataCacheSerializer::deliverPromises(std::vector<std::promise<void>> i_promises)
    {
        QTimer::singleShot(0, Qt::PreciseTimer, this,
                           [promises = std::make_shared<decltype(i_promises)>(std::move(i_promises))]() {
                               for (auto &promise : *promises)
                               {
                                   promise.set_value();
                               }
                           });
    }
 
    class SWIFT_MISC_EXPORT CDataCacheRevision::Session
    {
    public:
        // cppcheck-suppress missingReturn
        Session(const QString &filename) : m_filename(filename) {}
        void updateSession();
        const QUuid &uuid() const { return m_uuid; }
 
    private:
        const QString m_filename;
        QUuid m_uuid;
    };
 
    CDataCacheRevision::CDataCacheRevision(const QString &basename)
        : m_basename(basename), m_session(std::make_unique<Session>(m_basename + "/.session"))
    {}
 
    CDataCacheRevision::~CDataCacheRevision() = default; // Explicitly in cpp file
 
    CDataCacheRevision::LockGuard CDataCacheRevision::beginUpdate(const QMap<QString, qint64> &timestamps,
                                                                  bool updateUuid, bool pinsOnly)
    {
        QMutexLocker lock(&m_mutex);
 
        Q_ASSERT(!m_updateInProgress);
        Q_ASSERT(!m_lockFile.isLocked());
 
        if (!m_lockFile.lock())
        {
            CLogMessage(this).error(u"Failed to lock %1: %2") << m_basename << CFileUtils::lockFileError(m_lockFile);
            return {};
        }
        m_updateInProgress = true;
        LockGuard guard(this);
 
        m_timestamps.clear();
        m_originalTimestamps.clear();
 
        QFile revisionFile(CFileUtils::appendFilePaths(m_basename, ".rev"));
        if (m_found = revisionFile.exists(); m_found)
        {
            if (!revisionFile.open(QFile::ReadOnly | QFile::Text))
            {
                CLogMessage(this).error(u"Failed to open %1: %2")
                    << revisionFile.fileName() << revisionFile.errorString();
                return {};
            }
 
            auto json = QJsonDocument::fromJson(revisionFile.readAll()).object();
            if (json.contains("uuid") && json.contains("timestamps"))
            {
                m_originalTimestamps = fromJson(json.value("timestamps").toObject());
 
                QUuid id(json.value("uuid").toString());
                if (id == m_uuid && m_admittedQueue.isEmpty())
                {
                    if (m_pendingWrite)
                    {
                        return guard;
                    }
                    return {};
                }
                if (updateUuid)
                {
                    m_uuid = id;
                }
 
                auto timesToLive = fromJson(json.value("ttl").toObject());
                for (auto it = m_originalTimestamps.cbegin(); it != m_originalTimestamps.cend(); ++it)
                {
                    auto current = timestamps.value(it.key(), -1);
                    auto ttl = timesToLive.value(it.key(), -1);
                    if (current < it.value() && (ttl < 0 || QDateTime::currentMSecsSinceEpoch() < it.value() + ttl))
                    {
                        m_timestamps.insert(it.key(), it.value());
                    }
                }
                if (m_timestamps.isEmpty())
                {
                    if (m_pendingWrite)
                    {
                        return guard;
                    }
                    return {};
                }
 
                if (pinsOnly)
                {
                    auto pins = fromJson(json.value("pins").toArray());
                    for (const auto &key : m_timestamps.keys()) // clazy:exclude=container-anti-pattern,range-loop
                    {
                        if (!pins.contains(key))
                        {
                            m_timestamps.remove(key);
                        }
                    }
                }
 
                auto deferrals = fromJson(json.value("deferrals").toArray());
                m_admittedValues.unite(m_admittedQueue);
                if (updateUuid)
                {
                    m_admittedQueue.clear();
                }
                else if (!m_admittedQueue.isEmpty())
                {
                    m_admittedQueue.intersect(QSet<QString>(m_timestamps.keyBegin(), m_timestamps.keyEnd()));
                }
 
                for (const auto &key : m_timestamps.keys()) // clazy:exclude=container-anti-pattern,range-loop
                {
                    if (deferrals.contains(key) && !m_admittedValues.contains(key))
                    {
                        m_timestamps.remove(key);
                    }
                }
 
                m_session->updateSession();
                auto sessionIds = sessionFromJson(json.value("session").toObject());
                for (auto it = sessionIds.cbegin(); it != sessionIds.cend(); ++it)
                {
                    m_sessionValues[it.key()] = it.value();
                    if (it.value() != m_session->uuid())
                    {
                        m_timestamps.remove(it.key());
                        m_originalTimestamps.remove(it.key());
                    }
                }
            }
            else if (revisionFile.size() > 0)
            {
                CLogMessage(this).error(u"Invalid format of %1") << revisionFile.fileName();
 
                if (m_pendingWrite)
                {
                    return guard;
                }
                return {};
            }
            else
            {
                m_found = false;
            }
        }
 
        m_pendingRead = true;
        return guard;
    }
 
    void CDataCacheRevision::writeNewRevision(const QMap<QString, qint64> &i_timestamps,
                                              const QSet<QString> &excludeKeys)
    {
        QMutexLocker lock(&m_mutex);
 
        Q_ASSERT(m_updateInProgress);
        Q_ASSERT(m_lockFile.isLocked());
 
        CAtomicFile revisionFile(CFileUtils::appendFilePaths(m_basename, ".rev"));
        if (!revisionFile.open(QFile::WriteOnly | QFile::Text))
        {
            CLogMessage(this).error(u"Failed to open %1: %2") << revisionFile.fileName() << revisionFile.errorString();
            return;
        }
 
        m_uuid = CIdentifier().toUuid();
        auto timestamps = m_originalTimestamps;
        for (auto it = i_timestamps.cbegin(); it != i_timestamps.cend(); ++it)
        {
            if (it.value())
            {
                timestamps.insert(it.key(), it.value());
            }
        }
        for (const auto &key : excludeKeys)
        {
            timestamps.remove(key);
        }
 
        for (auto it = timestamps.cbegin(); it != timestamps.cend(); ++it)
        {
            if (m_sessionValues.contains(it.key()))
            {
                m_sessionValues[it.key()] = m_session->uuid();
            }
        }
 
        QJsonObject json;
        json.insert("uuid", m_uuid.toString());
        json.insert("timestamps", toJson(timestamps));
        json.insert("ttl", toJson(m_timesToLive));
        json.insert("pins", toJson(m_pinnedValues));
        json.insert("deferrals", toJson(m_deferredValues));
        json.insert("session", toJson(m_sessionValues));
        revisionFile.write(QJsonDocument(json).toJson());
 
        if (!revisionFile.checkedClose())
        {
            static const QString advice =
                QStringLiteral("If this error persists, try restarting your computer or delete the file manually.");
            CLogMessage(this).error(u"Failed to replace %1: %2 (%3)")
                << revisionFile.fileName() << revisionFile.errorString() << advice;
        }
    }
 
    void CDataCacheRevision::regenerate(const CValueCachePacket &keys)
    {
        QMutexLocker lock(&m_mutex);
 
        Q_ASSERT(m_updateInProgress);
        Q_ASSERT(m_lockFile.isLocked());
 
        writeNewRevision(m_originalTimestamps = keys.toTimestampMap());
    }
 
    void CDataCacheRevision::finishUpdate(bool keepPromises)
    {
        QMutexLocker lock(&m_mutex);
 
        Q_ASSERT(m_updateInProgress);
        Q_ASSERT(m_lockFile.isLocked());
 
        m_updateInProgress = false;
        m_pendingRead = false;
        m_pendingWrite = false;
        if (!keepPromises)
        {
            breakPromises();
        }
        m_lockFile.unlock();
    }
 
    bool CDataCacheRevision::isFound() const
    {
        QMutexLocker lock(&m_mutex);
 
        Q_ASSERT(m_updateInProgress);
        return m_found;
    }
 
    bool CDataCacheRevision::isPendingRead() const
    {
        QMutexLocker lock(&m_mutex);
 
        Q_ASSERT(m_updateInProgress);
        return !m_timestamps.isEmpty() || !m_found;
    }
 
    void CDataCacheRevision::notifyPendingWrite()
    {
        QMutexLocker lock(&m_mutex);
 
        m_pendingWrite = true;
    }
 
    QSet<QString> CDataCacheRevision::keysWithNewerTimestamps() const
    {
        QMutexLocker lock(&m_mutex);
 
        Q_ASSERT(m_updateInProgress);
        return { m_timestamps.keyBegin(), m_timestamps.keyEnd() };
    }
 
    const QMap<QString, qint64> &CDataCacheRevision::newerTimestamps() const
    {
        QMutexLocker lock(&m_mutex);
 
        Q_ASSERT(m_updateInProgress);
        return m_timestamps;
    }
 
    bool CDataCacheRevision::isNewerValueAvailable(const QString &key, qint64 timestamp)
    {
        QMutexLocker lock(&m_mutex);
 
        // Temporary guard object returned by beginUpdate is deleted at the end of the full expression,
        // don't try to split the conditional into multiple statements.
        // If a future is still waiting for the next update to begin, we don't want to break its associated promise.
        return (m_updateInProgress || m_pendingWrite || beginUpdate({ { key, timestamp } }, false).keepPromises()) &&
               (m_timestamps.contains(key) || m_admittedQueue.contains(key));
    }
 
    std::future<void> CDataCacheRevision::promiseLoadedValue(const QString &key, qint64 currentTimestamp)
    {
        QMutexLocker lock(&m_mutex);
 
        if (isNewerValueAvailable(key, currentTimestamp))
        {
            std::promise<void> promise;
            auto future = promise.get_future();
            m_promises.push_back(std::move(promise));
            return future;
        }
        return {};
    }
 
    std::vector<std::promise<void>> CDataCacheRevision::loadedValuePromises()
    {
        QMutexLocker lock(&m_mutex);
 
        Q_ASSERT(m_updateInProgress);
        return std::move(m_promises); // move into the return value, so m_promises becomes empty
    }
 
    void CDataCacheRevision::breakPromises()
    {
        QMutexLocker lock(&m_mutex);
 
        if (!m_promises.empty())
        {
            CLogMessage(this).debug() << "Breaking" << m_promises.size() << "promises";
            m_promises.clear();
        }
    }
 
    QString CDataCacheRevision::timestampsAsString() const
    {
        QMutexLocker lock(&m_mutex);
 
        QStringList result;
        for (auto it = m_timestamps.cbegin(); it != m_timestamps.cend(); ++it)
        {
            result.push_back(it.key() + "(" +
                             QDateTime::fromMSecsSinceEpoch(it.value(), QTimeZone::UTC).toString(Qt::ISODate) + ")");
        }
        return result.join(",");
    }
 
    void CDataCacheRevision::setTimeToLive(const QString &key, int ttl)
    {
        QMutexLocker lock(&m_mutex);
 
        Q_ASSERT(!m_updateInProgress);
        m_timesToLive.insert(key, ttl);
    }
 
    void CDataCacheRevision::overrideTimestamp(const QString &key, qint64 timestamp)
    {
        QMutexLocker lock(&m_mutex);
 
        Q_ASSERT(!m_updateInProgress);
        Q_ASSERT(!m_lockFile.isLocked());
 
        if (!m_lockFile.lock())
        {
            CLogMessage(this).error(u"Failed to lock %1: %2") << m_basename << CFileUtils::lockFileError(m_lockFile);
            m_lockFile.unlock();
            return;
        }
 
        CAtomicFile revisionFile(CFileUtils::appendFilePaths(m_basename, ".rev"));
        if (revisionFile.exists())
        {
            if (!revisionFile.open(QFile::ReadWrite | QFile::Text))
            {
                CLogMessage(this).error(u"Failed to open %1: %2")
                    << revisionFile.fileName() << revisionFile.errorString();
                m_lockFile.unlock();
                return;
            }
 
            auto json = QJsonDocument::fromJson(revisionFile.readAll()).object();
            auto timestamps = json.value("timestamps").toObject();
            timestamps.insert(key, timestamp);
            json.insert("timestamps", timestamps);
 
            if (revisionFile.seek(0) && revisionFile.resize(0) && revisionFile.write(QJsonDocument(json).toJson()))
            {
                if (!revisionFile.checkedClose())
                {
                    static const QString advice = QStringLiteral(
                        "If this error persists, try restarting your computer or delete the file manually.");
                    CLogMessage(this).error(u"Failed to replace %1: %2 (%3)")
                        << revisionFile.fileName() << revisionFile.errorString() << advice;
                }
            }
            else
            {
                CLogMessage(this).error(u"Failed to write to %1: %2")
                    << revisionFile.fileName() << revisionFile.errorString();
            }
        }
        m_lockFile.unlock();
    }
 
    qint64 CDataCacheRevision::getTimestampOnDisk(const QString &key)
    {
        QMutexLocker lock(&m_mutex);
 
        if (m_lockFile.isLocked())
        {
            return m_originalTimestamps.value(key);
        }
 
        if (!m_lockFile.lock())
        {
            CLogMessage(this).error(u"Failed to lock %1: %2") << m_basename << CFileUtils::lockFileError(m_lockFile);
            m_lockFile.unlock();
            return 0;
        }
 
        qint64 result = 0;
        QFile revisionFile(CFileUtils::appendFilePaths(m_basename, ".rev"));
        if (revisionFile.exists())
        {
            if (revisionFile.open(QFile::ReadOnly | QFile::Text))
            {
                auto json = QJsonDocument::fromJson(revisionFile.readAll()).object();
                result = static_cast<qint64>(json.value("timestamps").toObject().value(key).toDouble());
            }
            else
            {
                CLogMessage(this).error(u"Failed to open %1: %2")
                    << revisionFile.fileName() << revisionFile.errorString();
            }
        }
        m_lockFile.unlock();
        return result;
    }
 
    void CDataCacheRevision::pinValue(const QString &key)
    {
        QMutexLocker lock(&m_mutex);
 
        Q_ASSERT(!m_updateInProgress);
        m_pinnedValues.insert(key);
    }
 
    void CDataCacheRevision::deferValue(const QString &key)
    {
        QMutexLocker lock(&m_mutex);
 
        Q_ASSERT(!m_updateInProgress);
        m_deferredValues.insert(key);
    }
 
    void CDataCacheRevision::admitValue(const QString &key)
    {
        QMutexLocker lock(&m_mutex);
 
        m_admittedQueue.insert(key);
    }
 
    void CDataCacheRevision::sessionValue(const QString &key)
    {
        QMutexLocker lock(&m_mutex);
 
        Q_ASSERT(!m_updateInProgress);
        m_sessionValues[key]; // clazy:exclude=detaching-member
    }
 
    QJsonObject CDataCacheRevision::toJson(const QMap<QString, qint64> &timestamps)
    {
        QJsonObject result;
        for (auto it = timestamps.begin(); it != timestamps.end(); ++it)
        {
            result.insert(it.key(), it.value());
        }
        return result;
    }
 
    QMap<QString, qint64> CDataCacheRevision::fromJson(const QJsonObject &timestamps)
    {
        QMap<QString, qint64> result;
        for (auto it = timestamps.begin(); it != timestamps.end(); ++it)
        {
            result.insert(it.key(), static_cast<qint64>(it.value().toDouble()));
        }
        return result;
    }
 
    QJsonArray CDataCacheRevision::toJson(const QSet<QString> &pins)
    {
        QJsonArray result;
        for (const auto &pin : pins)
        {
            result.push_back(pin);
        }
        return result;
    }
 
    QSet<QString> CDataCacheRevision::fromJson(const QJsonArray &pins)
    {
        QSet<QString> result;
        for (auto pin : pins)
        {
            result.insert(pin.toString());
        }
        return result;
    }
 
    QJsonObject CDataCacheRevision::toJson(const QMap<QString, QUuid> &timestamps)
    {
        QJsonObject result;
        for (auto it = timestamps.begin(); it != timestamps.end(); ++it)
        {
            result.insert(it.key(), it.value().toString());
        }
        return result;
    }
 
    QMap<QString, QUuid> CDataCacheRevision::sessionFromJson(const QJsonObject &session)
    {
        QMap<QString, QUuid> result;
        for (auto it = session.begin(); it != session.end(); ++it)
        {
            result.insert(it.key(), QUuid(it.value().toString()));
        }
        return result;
    }
 
    void CDataCacheRevision::Session::updateSession()
    {
        CAtomicFile file(m_filename);
        bool ok = file.open(QIODevice::ReadWrite | QFile::Text);
        if (!ok)
        {
            CLogMessage(this).error(u"Failed to open session file %1: %2") << m_filename << file.errorString();
            return;
        }
        auto json = QJsonDocument::fromJson(file.readAll()).object();
        QUuid id(json.value("uuid").toString());
        CSequence<CProcessInfo> apps;
        auto status = apps.convertFromJsonNoThrow(json.value("apps").toObject(), this,
                                                  QStringLiteral("Error in %1 apps object").arg(m_filename));
        apps.removeIf([](const CProcessInfo &pi) { return !pi.exists(); });
 
        if (apps.isEmpty())
        {
            id = CIdentifier().toUuid();
        }
        m_uuid = id;
 
        CProcessInfo currentProcess = CProcessInfo::currentProcess();
        Q_ASSERT(currentProcess.exists());
        apps.replaceOrAdd(currentProcess);
        json.insert("apps", apps.toJson());
        json.insert("uuid", m_uuid.toString());
        if (file.seek(0) && file.resize(0) && file.write(QJsonDocument(json).toJson()))
        {
            if (!file.checkedClose())
            {
                static const QString advice =
                    QStringLiteral("If this error persists, try restarting your computer or delete the file manually.");
                CLogMessage(this).error(u"Failed to replace %1: %2 (%3)")
                    << file.fileName() << file.errorString() << advice;
            }
        }
        else
        {
            CLogMessage(this).error(u"Failed to write to %1: %2") << file.fileName() << file.errorString();
        }
    }
 
} // namespace swift::misc