內存映射文件不能用，只是創建它的進程

Question

我針對.NET Framework 3.5的發現（4.0+可悲的是不是這個項目的一個選項）在64位的Windows 8，我原本以爲問題是，由ProcessA作出的內存映射文件不容易找到的進程B，但即使不ProcessA可以找到剛纔保存的文件，即使手感好，可用於書寫和讀取文件。在代碼示例中，我在調用CreateFileMapping之後立即調用OpenFileMapping，但即使在將數據寫入文件之後它仍然失敗。我已經使用了與文件映射的CreateFileMapping屬性，使其長傳入0，使其成爲一個SECURITY_ATTRIBUTES結構和IntPtr.Zero傳遞的lpSecurityDescriptor，都沒有快樂。我也嘗試過FileMapAccess ReadWrite和AllAccess。我也試着讓memoryfilename不是常量。我沒有看到爲什麼無法找到映射文件，甚至無法找到創建映射文件的過程。這裏所涉及的代碼的梗概：

private IntPtr hHandle; 
private IntPtr INVALID_HANDLE_VALUE = new IntPtr(-1); 
public const Int64 FILESIZE = 1024 * 1024; 
private const string memoryfilename = "myfilename"; 

//CreateFileMapping 
[DllImport("kernel32.dll", SetLastError = true, CharSet = CharSet.Auto)] 
static extern IntPtr CreateFileMapping(
IntPtr hFile, 
IntPtr lpFileMappingAttributes, 
FileMapProtection flProtect, 
uint dwMaximumSizeHigh, 
uint dwMaximumSizeLow, 
[MarshalAs(UnmanagedType.LPStr)] string lpName); 

//OpenFileMapping 
[DllImport("kernel32.dll", SetLastError = true)] 
static extern IntPtr OpenFileMapping(
FileMapAccess dwDesiredAccess, 
Int32 bInheritHandle, 
[MarshalAs(UnmanagedType.LPStr)] string lpName); 

[Flags] 
public enum FileMapAccess : uint 
{ 
    FileMapCopy = 0x0001, 
    FileMapWrite = 0x0002, 
    FileMapRead = 0x0004, 
    FileMapReadWrite = 0x0006, 
    FileMapAllAccess = 0x001f, 
    FileMapExecute = 0x0020, 
} 

[Flags] 
enum FileMapProtection : uint 
{ 
    PageReadonly = 0x02, 
    PageReadWrite = 0x04, 
    PageWriteCopy = 0x08, 
    PageExecuteRead = 0x20, 
    PageExecuteReadWrite = 0x40, 
    SectionCommit = 0x8000000, 
    SectionImage = 0x1000000, 
    SectionNoCache = 0x10000000, 
    SectionReserve = 0x4000000, 
} 

//hHandle becomes non-zero 
hHandle= CreateFileMapping(
INVALID_HANDLE_VALUE, IntPtr.Zero, FileMapProtection.PageReadWrite, 
(uint)0, (uint)FILESIZE, memoryfilename); 

//hHandle2 stays zero 
IntPtr hHandle2 = OpenFileMapping(FileMapAccess.FileMapWrite, 0, memoryfilename); 

//myerror is 2 ERROR_FILE_NOT_FOUND 
uint myerror = GetLastError(); 

//this works and I can read/write the file through UnmanagedMemoryStream 
pBuffer = MapViewOfFile(hHandle, FileMapAccess.FileMapWrite, 0, 0, (uint)FILESIZE); 

Answer 1

[DllImport("kernel32.dll", SetLastError = true, CharSet = CharSet.Auto)] 
static extern IntPtr CreateFileMapping(
    IntPtr hFile, 
    IntPtr lpFileMappingAttributes, 
    FileMapProtection flProtect, 
    uint dwMaximumSizeHigh, 
    uint dwMaximumSizeLow, 
    [MarshalAs(UnmanagedType.LPStr)] 
    string lpName 
); 

的DllImport屬性使用CharSet.Auto這意味着函數的寬字符版本將被使用。然後您傳遞ANSI編碼的字符串，因爲您使用了UnmanagedType.LPStr。正如漢斯所說，這意味着當系統解釋你所提供的ANSI編碼文本，就好像它是UTF-16編碼一樣，你的名字就會被破壞。

[DllImport("kernel32.dll", SetLastError = true)] 
static extern IntPtr OpenFileMapping(
    FileMapAccess dwDesiredAccess, 
    Int32 bInheritHandle, 
    [MarshalAs(UnmanagedType.LPStr)] 
    string lpName 
); 

這個時候你忽略CharSet.Auto等的``CharSet.Ansi is used. And so the ANSI version of the function is used, which matches UnmanagedType.LPStr`此時默認。因此傳遞了預期的名稱。

這一切都說明了爲什麼系統會報告ERROR_FILE_NOT_FOUND。

修復的P/Invoke聲明和一切都會好的。

[DllImport("kernel32.dll", SetLastError = true, CharSet = CharSet.Unicode)] 
static extern IntPtr CreateFileMapping(
    IntPtr hFile, 
    IntPtr lpFileMappingAttributes, 
    FileMapProtection flProtect, 
    uint dwMaximumSizeHigh, 
    uint dwMaximumSizeLow, 
    string lpName 
); 

[DllImport("kernel32.dll", SetLastError = true, CharSet = CharSet.Unicode)] 
static extern IntPtr OpenFileMapping(
    FileMapAccess dwDesiredAccess, 
    bool bInheritHandle, 
    string lpName 
);