並行壓縮C＃

Question

是否可以使用Parallel.Foreach或其他方式優化此代碼？

using (var zipStream = new ZipOutputStream(OpenWriteArchive()))
{
    zipStream.CompressionLevel = CompressionLevel.Level9;    
    foreach (var document in docuemnts)
    {
        zipStream.PutNextEntry(GetZipEntryName(type));    
        using (var targetStream = new MemoryStream()) // document stream
        {
            DocumentHelper.SaveDocument(document.Value, targetStream, type);    
            targetStream.Position = 0; targetStream.CopyTo(zipStream);
        }    
        GC.Collect();
    };
}

問題是DotNetZip和SharpZipLib的ZipOutputStream不支持位置更改或搜索。

從多個線程寫入zip流會導致錯誤。 將結果流累積到ConcurrentStack中也是不可能的，因為應用程序可以處理1000多個文檔，並且應該將流實時壓縮並保存到雲中。

有什么辦法解決這個問題？

Answer 1

通過使用ProducerConsumerQueue （生產者－消費者模式）解決。

using (var queue = new ProducerConsumerQueue<byte[]>(HandlerDelegate))
{
    Parallel.ForEach(documents, document =>
    {
        using (var documentStream = new MemoryStream())
        {
            // saving document here ...

            queue.EnqueueTask(documentStream.ToArray());
        }
    });
}

protected void HandlerDelegate(byte[] content)
{
    ZipOutputStream.PutNextEntry(Guid.NewGuid() + ".pdf");

    using (var stream = new MemoryStream(content))
    {
        stream.Position = 0; stream.CopyTo(ZipOutputStream);
    }
}

Answer 2

嘗試在並行foreach中清除zipstream，例如：

Parallel.ForEach(docuemnts, (document) =>
            {
                using (var zipStream = new ZipOutputStream(OpenWriteArchive()))
                {
                    zipStream.CompressionLevel = CompressionLevel.Level9;
                    zipStream.PutNextEntry(GetZipEntryName(type));
                    using (var targetStream = new MemoryStream()) // document stream
                    {
                        DocumentHelper.SaveDocument(document.Value, targetStream, type);
                        targetStream.Position = 0; targetStream.CopyTo(zipStream);
                    }
                    GC.Collect();
                }
            });

再見！