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我有一段代码需要使用 UNC 路径从 NAS 服务器打开和读取大量小文本文件。此代码是最初用 C++ 编写但现在正在转换为 C# 的模块的一部分。C# 版本要慢得多。我确定打开文件的调用几乎是所有性能差异的原因。使用 WireShark 我发现这是因为 System.IO.File.Open 调用比类似的 C++ 代码发出的 SMB 网络请求要多得多。

C++ 代码进行此调用：

FILE *f = _wfsopen(fileName, L"r", _SH_DENYWR);

这会产生以下 SMB 请求序列：

NT Create AndX Request, FID: 0x0004, Path: \\a\\i\\a\\q\\~141106162638847.nmd
NT Create AndX Response, FID: 0x0004
Trans2 Request, QUERY_FILE_INFO, FID: 0x0004, Query File Basic Info
Trans2 Response, FID: 0x0004, QUERY_FILE_INFO
Read AndX Request, FID: 0x0004, 1327 bytes at offset 0
Read AndX Response, FID: 0x0004, 1327 bytes
Close Request, FID: 0x0004
Close Response, FID: 0x0004
NT Create AndX Request, FID: 0x0005, Path: \\a\\i\\a\\q\\~141106162638847.nmd
NT Create AndX Response, FID: 0x0005

C# 代码进行此调用：

FileStream f = File.Open(fileName, FileMode.Open, FileAccess.Read, FileShare.Read);

这会产生以下 SMB 请求序列：

Trans2 Request, QUERY_PATH_INFO, Query File Basic Info, Path: \\a\\i\\a\\q\\~141106162638847.nmd
Trans2 Response, QUERY_PATH_INFO
Trans2 Request, QUERY_PATH_INFO, Query File Standard Info, Path: \\a\\i\\a\\q\\~141106162638847.nmd
Trans2 Response, QUERY_PATH_INFO
Trans2 Request, QUERY_PATH_INFO, Query File Basic Info, Path: \\a\\i\\a\\q\\~141106162638847.nmd
Trans2 Response, QUERY_PATH_INFO
Trans2 Request, QUERY_PATH_INFO, Query File Basic Info, Path: 
Trans2 Response, QUERY_PATH_INFO
Trans2 Request, QUERY_PATH_INFO, Query File Standard Info, Path: 
Trans2 Response, QUERY_PATH_INFO
Trans2 Request, FIND_FIRST2, Pattern: \\a
Trans2 Response, FIND_FIRST2, Files: a
Trans2 Request, QUERY_PATH_INFO, Query File Basic Info, Path: \\a
Trans2 Response, QUERY_PATH_INFO
Trans2 Request, QUERY_PATH_INFO, Query File Standard Info, Path: \\a
Trans2 Response, QUERY_PATH_INFO
Trans2 Request, FIND_FIRST2, Pattern: \\a\\i
Trans2 Response, FIND_FIRST2, Files: i
Trans2 Request, QUERY_PATH_INFO, Query File Basic Info, Path: \\a\\i
Trans2 Response, QUERY_PATH_INFO
Trans2 Request, QUERY_PATH_INFO, Query File Standard Info, Path: \\a\\i
Trans2 Response, QUERY_PATH_INFO
Trans2 Request, FIND_FIRST2, Pattern: \\a\\i\\a
Trans2 Response, FIND_FIRST2, Files: a
Trans2 Request, QUERY_PATH_INFO, Query File Basic Info, Path: \\a\\i\\a
Trans2 Response, QUERY_PATH_INFO
Trans2 Request, QUERY_PATH_INFO, Query File Standard Info, Path: \\a\\i\\a
Trans2 Response, QUERY_PATH_INFO
Trans2 Request, FIND_FIRST2, Pattern: \\a\\i\\a\\q
Trans2 Response, FIND_FIRST2, Files: q
Trans2 Request, QUERY_PATH_INFO, Query File Basic Info, Path: \\a\\i\\a\\q\\~141106162638847.nmd
Trans2 Response, QUERY_PATH_INFO
Trans2 Request, QUERY_PATH_INFO, Query File Standard Info, Path: \\a\\i\\a\\q\\~141106162638847.nmd
Trans2 Response, QUERY_PATH_INFO
Trans2 Request, QUERY_PATH_INFO, Query File Basic Info, Path: \\a\\i\\a\\q\\~141106162638847.nmd
Trans2 Response, QUERY_PATH_INFO
Trans2 Request, QUERY_PATH_INFO, Query File Basic Info, Path: 
Trans2 Response, QUERY_PATH_INFO
Trans2 Request, QUERY_PATH_INFO, Query File Standard Info, Path: 
Trans2 Response, QUERY_PATH_INFO
Trans2 Request, FIND_FIRST2, Pattern: \\a
Trans2 Response, FIND_FIRST2, Files: a
Trans2 Request, QUERY_PATH_INFO, Query File Basic Info, Path: \\a
Trans2 Response, QUERY_PATH_INFO
Trans2 Request, QUERY_PATH_INFO, Query File Standard Info, Path: \\a
Trans2 Response, QUERY_PATH_INFO
Trans2 Request, FIND_FIRST2, Pattern: \\a\\i
Trans2 Response, FIND_FIRST2, Files: i
Trans2 Request, QUERY_PATH_INFO, Query File Basic Info, Path: \\a\\i
Trans2 Response, QUERY_PATH_INFO
Trans2 Request, QUERY_PATH_INFO, Query File Standard Info, Path: \\a\\i
Trans2 Response, QUERY_PATH_INFO
Trans2 Request, FIND_FIRST2, Pattern: \\a\\i\\a
Trans2 Response, FIND_FIRST2, Files: a
Trans2 Request, QUERY_PATH_INFO, Query File Basic Info, Path: \\a\\i\\a
Trans2 Response, QUERY_PATH_INFO
Trans2 Request, QUERY_PATH_INFO, Query File Standard Info, Path: \\a\\i\\a
Trans2 Response, QUERY_PATH_INFO
Trans2 Request, FIND_FIRST2, Pattern: \\a\\i\\a\\q
Trans2 Response, FIND_FIRST2, Files: q
Close Request, FID: 0x000f
Close Response
NT Create AndX Request, FID: 0x0018, Path: \\a\\i\\a\\q\\~141106162638847.nmd
NT Create AndX Response, FID: 0x0018
Trans2 Request, QUERY_FILE_INFO, FID: 0x0018, Query File Basic Info
Trans2 Response, FID: 0x0018, QUERY_FILE_INFO
Read AndX Request, FID: 0x0018, 1327 bytes at offset 0
Read AndX Response, FID: 0x0018, 1327 bytes
Close Request, FID: 0x0018
Close Response, FID: 0x0018
NT Create AndX Request, FID: 0x0019, Path: \\a\\i\\a\\q\\~141106162638847.nmd
NT Create AndX Response, FID: 0x0019

为什么 System.IO.File.Open 会发出所有这些额外的 SMB 请求？有什么方法可以更改此代码以避免所有这些额外的请求？

4

2 回答 2

12

简而言之，File.Open 调用new FileStream()并new FileStream()执行了很多调用：

  1. 规范化路径。

    String filePath = Path.NormalizePath(path, true, maxPath); // fullCheck: true

导致此代码：

1.a：获取完整路径：

    if (fullCheck) { ... 
        result = newBuffer.GetFullPathName();

GetFullPathName()调用Win32Native.GetFullPathName一到两次（取决于生成路径的长度）。

1.b。试图扩大短路径。您的路径包含字符，因此它看起来像是路径扩展~的候选者：

    if (mightBeShortFileName) {
        bool r = newBuffer.TryExpandShortFileName();

结果，Win32Native.GetLongPathName()被调用。

  1. FileIoPermission.Demand()（仅适用于不受信任的）：

    // All demands in full trust domains are no-ops, so skip 
if (!CodeAccessSecurityEngine.QuickCheckForAllDemands()) {
    ...
    new FileIOPermission(secAccess, control, new String[] { filePath }, false, false).Demand();

  2. 打开fileStream（软盘反击；））：

     // Don't pop up a dialog for reading from an emtpy floppy drive
int oldMode = Win32Native.SetErrorMode(Win32Native.SEM_FAILCRITICALERRORS);
try {
    ...
    _handle = Win32Native.SafeCreateFile(tempPath, fAccess, share, secAttrs, mode, flagsAndAttributes, IntPtr.Zero);

  3. Win32Native.GetFileType()

并非所有这些都会导致 smb 请求，但有些会。我试图通过逐步调试源代码（这里是启用 .net 源代码调试的手册）并在每一步后检查日志来重现聊天请求。结果与您的第一个列表更相似。如果你真的有兴趣找到真正的问题，你必须自己做。

UPD请注意，我已经检查了当前 (.net 4.5.2) 的行为。自 2.0 以来它被多次更改（例如FileIOPermission.Demand()，最初也被称为完全受信任的代码），所以它取决于:)

于 2014-12-03T06:58:48.090 回答
7

对于为什么 .NET 实现如此健谈，我真的没有具体的答案，但这种行为是由于实现的原因，System.IO.FileStream因为File.Open(fileName, FileMode.Open, FileAccess.Read, FileShare.Read);所做的只是将参数传递给FileStream 构造函数。

public static FileStream Open(string path, FileMode mode, FileAccess access, FileShare share)
{
    return new FileStream(path, mode, access, share);
}

更改 FileStream 的行为意味着您基本上必须重新实现 FileStream 类，这需要付出很多努力。

您的另一个更简单的替代方法是创建一个调用您提供的 C++ 代码的本机包装器。然后从您的 C# 代码中调用本机包装器。

于 2014-11-25T23:35:19.130 回答