Method readFile

src/Disks/DiskCacheWrapper.cpp:107–179

}

std::unique_ptr<ReadBufferFromFileBase>
DiskCacheWrapper::readFile(
    const String & path,
    const ReadSettings& settings) const
{
    if (!cache_file_predicate(path))
        return DiskDecorator::readFile(path, settings);

    LOG_DEBUG(log, "Read file {} from cache", backQuote(path));

    if (cache_disk->exists(path))
        return cache_disk->readFile(path, settings);

    auto metadata = acquireDownloadMetadata(path);

    {
        std::unique_lock<std::mutex> lock{mutex};

        if (metadata->status == NONE)
        {
            /// This thread will responsible for file downloading to cache.
            metadata->status = DOWNLOADING;
            LOG_DEBUG(log, "File {} doesn't exist in cache. Will download it", backQuote(path));
        }
        else if (metadata->status == DOWNLOADING)
        {
            LOG_DEBUG(log, "Waiting for file {} download to cache", backQuote(path));
            metadata->condition.wait(lock, [metadata] { return metadata->status == DOWNLOADED || metadata->status == ERROR; });
        }
    }

    if (metadata->status == DOWNLOADING)
    {
        FileDownloadStatus result_status = DOWNLOADED;

        if (!cache_disk->exists(path))
        {
            try
            {
                auto dir_path = directoryPath(path);
                if (!cache_disk->exists(dir_path))
                    cache_disk->createDirectories(dir_path);

                auto tmp_path = path + ".tmp";
                {
                    auto src_buffer = DiskDecorator::readFile(path, settings);
                    auto dst_buffer = cache_disk->writeFile(tmp_path, {.buffer_size = settings.local_fs_buffer_size, .mode = WriteMode::Rewrite});
                    copyData(*src_buffer, *dst_buffer);
                }
                cache_disk->moveFile(tmp_path, path);

                LOG_DEBUG(log, "File {} downloaded to cache", backQuote(path));
            }
            catch (...)
            {
                tryLogCurrentException("DiskCache", "Failed to download file + " + backQuote(path) + " to cache");
                result_status = ERROR;
            }