Question

我正在尝试构建一个分布式计算系统，该系统使用内存映射文件通过VBA协调多个联网PC之间的工作。换句话说，我想让一组联网的计算机同时以协调的方式在一个项目上工作，这个项目可以很容易地分成不同的部分。一台PC需要13个多小时才能完成项目，这对我的客户来说并不实用。

我想将信息存储在内存映射文件中，以帮助PC以协调的方式处理项目（即没有重复工作，避免竞争问题等）。我尝试使用其他类型的文件来完成此操作，这会导致文件争用问题，或者需要很长时间。所以，正如本论坛所建议的，我正在尝试内存映射文件。

我是内存映射文件和分布式计算的新手。必须在VBA中完成。据我所知，我必须指定将文件保存在我们网络上的目录（这里是驱动器Z），所有PC都可以访问。我拼凑了来自不同地方的一些代码：

Option Explicit

Private Const PAGE_READWRITE As Long = &H4
Private Const FILE_MAP_WRITE As Long = &H2
Private Const GENERIC_READ = &H80000000
Private Const GENERIC_WRITE = &H40000000
Private Const OPEN_ALWAYS = 4
Private Const FILE_ATTRIBUTE_NORMAL = &H80

Private Declare Function CreateFile Lib "kernel32" Alias "CreateFileA" (ByVal lpFileName As String, _
                                         ByVal dwDesiredAccess As Long, ByVal dwShareMode As Long, _
                                         ByVal lpSecurityAttributes As Long, ByVal dwCreationDisposition As Long, _
                                         ByVal dwFlagsAndAttributes As Long, ByVal hTemplateFile As Long) As Long

Private Declare Function CreateFileMapping Lib "kernel32.dll" Alias "CreateFileMappingA" ( _
     ByVal hFile As Long, _
     ByVal lpFileMappigAttributes As Long, _
     ByVal flProtect As Long, _
     ByVal dwMaximumSizeHigh As Long, _
     ByVal dwMaximumSizeLow As Long, _
     ByVal lpName As String) As Long

Private Declare Function MapViewOfFile Lib "kernel32.dll" ( _
     ByVal hFileMappingObject As Long, _
     ByVal dwDesiredAccess As Long, _
     ByVal dwFileOffsetHigh As Long, _
     ByVal dwFileOffsetLow As Long, _
     ByVal dwNumberOfBytesToMap As Long) As Long

#If VBA7 Then
Public Declare PtrSafe Sub CopyMemory Lib "kernel32" Alias _
    "RtlMoveMemory" (destination As Any, source As Any, _
    ByVal length As Long)
#Else
Public Declare Sub CopyMemory Lib "kernel32" Alias _
    "RtlMoveMemory" (destination As Any, source As Any, _
    ByVal length As Long)
    #End If

Private Declare Function UnmapViewOfFile Lib "kernel32.dll" ( _
     ByRef lpBaseAddress As Any) As Long

Private Declare Function CloseHandle Lib "kernel32.dll" ( _
     ByVal hObject As Long) As Long

Private hMMF As Long
Private pMemFile As Long

Sub IntoMemoryFileOutOfMemoryFile()

    Dim sFile As String
    Dim hFile As Long

    sFile = "Z:\path\test1.txt"

    hFile = CreateFile(sFile, GENERIC_READ Or GENERIC_WRITE, 0, 0, OPEN_ALWAYS, FILE_ATTRIBUTE_NORMAL, 0)
    hMMF = CreateFileMapping(hFile, 0, PAGE_READWRITE, 0, 1000000, "MyMemoryMappedFile")

    pMemFile = MapViewOfFile(hMMF, FILE_MAP_WRITE, 0, 0, 0)

    Dim buffer As String

    buffer = "testing1"
    CopyMemory pMemFile, ByVal buffer, 128

    hMMF = CreateFileMapping(-1, 0, PAGE_READWRITE, 0, 1000000, "MyMemoryMappedFile")
    pMemFile = MapViewOfFile(hMMF, FILE_MAP_WRITE, 0, 0, 0)

     Dim buffer2 As String

    buffer2 = String$(128, vbNullChar)

     CopyMemory ByVal buffer2, pMemFile, 128

     MsgBox buffer2 & " < - it worked?"

     UnmapViewOfFile pMemFile
     CloseHandle hMMF
End Sub

作为一个小例子，上面的代码试图把字符串＆＃34; testing1＆＃34;然后在文件test1.txt中检索该字符串并将其存储在变量buffer2中，最后通过msgbox显示该字符串。超级简单。但是，我不知道我在做什么。

我们所有的电脑都是64位，Windows 7，Office / Excel 2013.

问题/问题：

运行IntoMemoryFileOutOfMemoryFile时，msgbox为空白
在sub完成之后，我打开test1.txt，得到：＆＃34;进程无法访问该文件，因为它正被另一个进程使用。＆＃34;这告诉我我没有正确使用UnmapViewOfFile和/或CloseHandle。
我想让这些内存文件保持不变，所以如果所有的PC都被中断，我可以重新启动进程并从中断的地方继续。

以下是我过去常常获得的一些链接：

有趣但不重要的信息：＆＃34;项目＆＃34;是针对对冲基金的客户。我是一个基本定量的财务人员。我们每天在1250多个数据领域分析2000多个股票，以制定买卖股票，期货和期权的宏观经济信号/预测。

更新：如果我分别更改这两个CopyMemory行（按值传递pMemFile）：

CopyMemory ByVal pMemFile, buffer, 128

和...

CopyMemory buffer2, ByVal pMemFile, 128

我在文件test1.txt和excel崩溃中得到了一堆疯狂的角色。

Answer 1

对于您的第一个问题（避免探索太多），这与您尝试将buffer传递给RtlMoveMemory的方式有关。它期待一个指针，但你传递了BSTR的副本。还记得VBA中的String是Unicode，所以你会得到交织的空字符。我通常使用字节数组或变体（它们将被编组到CSTR）。

对于您的第二个问题，该文件被锁定，因为您永远不会释放hFile的句柄。事实上，只要您将其传递给CreateFileMappingA，就可以在CloseHandle上致电hFile。

对于第三个问题，当您进行第二次调用时，您正在覆盖句柄hMMF和指针pMemFile。从理论上讲，它们应该返回与您在同一过程中相同的句柄和指针，但这并不能真正测试您是否获得了地图视图。

至于内存访问，我可能会建议将整个事物包装在一个Class中，并将指针映射到比调用RtlMoveMemory更有用的东西。我将我在问题中链接的代码调整为一个类，它应该使它更安全，更可靠，更方便使用（尽管它仍然需要通过错误检查来充实）：

'Class MemoryMap
Option Explicit

Private Type SafeBound
    cElements As Long
    lLbound As Long
End Type

Private Type SafeArray
    cDim As Integer
    fFeature As Integer
    cbElements As Long
    cLocks As Long
    pvData As Long
    rgsabound As SafeBound
End Type

Private Const VT_BY_REF = &H4000&
Private Const FILE_ATTRIBUTE_NORMAL = &H80
Private Const OPEN_ALWAYS = &H4
Private Const GENERIC_READ = &H80000000
Private Const GENERIC_WRITE = &H40000000
Private Const PAGE_READWRITE = &H4
Private Const FILE_MAP_WRITE = &H2
Private Const FADF_FIXEDSIZE = &H10

Private cached As SafeArray
Private buffer() As Byte
Private hFileMap As Long
Private hMM As Long
Private mapped_file As String
Private bound As Long

Public Property Get FileName() As String
    FileName = mapped_file
End Property

Public Property Get length() As Long
    length = bound
End Property

Public Sub WriteData(inVal As String, offset As Long)
    Dim temp() As Byte
    temp = StrConv(inVal, vbFromUnicode)

    Dim index As Integer
    For index = 0 To UBound(temp)
        buffer(index + offset) = temp(index)
    Next index
End Sub

Public Function ReadData(offset, length) As String
    Dim temp() As Byte
    ReDim temp(length)

    Dim index As Integer
    For index = 0 To length - 1
        temp(index) = buffer(index + offset)
    Next index

    ReadData = StrConv(temp, vbUnicode)
End Function

Public Function OpenMapView(file_path As String, size As Long, mapName As String) As Boolean
    bound = size
    mapped_file = file_path

    Dim hFile As Long
    hFile = CreateFile(file_path, GENERIC_READ Or GENERIC_WRITE, 0, 0, OPEN_ALWAYS, FILE_ATTRIBUTE_NORMAL, 0)
    hFileMap = CreateFileMapping(hFile, 0, PAGE_READWRITE, 0, size, mapName)
    CloseHandle hFile
    hMM = MapViewOfFile(hFileMap, FILE_MAP_WRITE, 0, 0, 0)

    ReDim buffer(2)
    'Cache the original SafeArray structure to allow re-mapping for garbage collection.
    If Not ReadSafeArrayInfo(buffer, cached) Then
        'Something's wrong, close our handles.
        CloseOpenHandles
        Exit Function
    End If

    Dim temp As SafeArray
    If ReadSafeArrayInfo(buffer, temp) Then
        temp.cbElements = 1
        temp.rgsabound.cElements = size
        temp.fFeature = temp.fFeature And FADF_FIXEDSIZE
        temp.pvData = hMM
        OpenMapView = SwapArrayInfo(buffer, temp)
    End If    
End Function

Private Sub Class_Terminate()
    'Point the member array back to its own data for garbage collection.
    If UBound(buffer) = 2 Then
        SwapArrayInfo buffer, cached
    End If
    SwapArrayInfo buffer, cached
    CloseOpenHandles
End Sub

Private Sub CloseOpenHandles()
    If hMM > 0 Then UnmapViewOfFile hMM
    If hFileMap > 0 Then CloseHandle hFileMap
End Sub

Private Function GetBaseAddress(vb_array As Variant) As Long
    Dim vtype As Integer
    'First 2 bytes are the VARENUM.
    CopyMemory vtype, vb_array, 2
    Dim lp As Long
    'Get the data pointer.
    CopyMemory lp, ByVal VarPtr(vb_array) + 8, 4
    'Make sure the VARENUM is a pointer.
    If (vtype And VT_BY_REF) <> 0 Then
        'Dereference it for the actual data address.
        CopyMemory lp, ByVal lp, 4
        GetBaseAddress = lp
    End If
End Function

Private Function ReadSafeArrayInfo(vb_array As Variant, com_array As SafeArray) As Boolean
    If Not IsArray(vb_array) Then Exit Function

    Dim lp As Long
    lp = GetBaseAddress(vb_array)
    If lp > 0 Then
        With com_array
            'Copy it over the passed structure
            CopyMemory .cDim, ByVal lp, 16
            'Currently doesn't support multi-dimensional arrays.
            If .cDim = 1 Then
                CopyMemory .rgsabound, ByVal lp + 16, LenB(.rgsabound)
                ReadSafeArrayInfo = True
            End If
        End With
    End If
End Function

Private Function SwapArrayInfo(vb_array As Variant, com_array As SafeArray) As Boolean
    If Not IsArray(vb_array) Then Exit Function
    Dim lp As Long
    lp = GetBaseAddress(vb_array)

    With com_array
        'Overwrite the passed array with the SafeArray structure.
        CopyMemory ByVal lp, .cDim, 16
        If .cDim = 1 Then
            CopyMemory ByVal lp + 16, .rgsabound, LenB(.rgsabound)
            SwapArrayInfo = True
        End If
    End With    
End Function

用法是这样的：

Private Sub MMTest()
    Dim mm As MemoryMap

    Set mm = New MemoryMap
    If mm.OpenMapView("C:\Dev\test.txt", 1000, "TestMM") Then
        mm.WriteData "testing1", 0
        Debug.Print mm.ReadData(0, 8)
    End If

    Set mm = Nothing
End Sub

您还需要以下声明：

Public Declare Function MapViewOfFile Lib "kernel32.dll" ( _
    ByVal hFileMappingObject As Long, _
    ByVal dwDesiredAccess As Long, _
    ByVal dwFileOffsetHigh As Long, _
    ByVal dwFileOffsetLow As Long, _
    ByVal dwNumberOfBytesToMap As Long) As Long

Public Declare Sub CopyMemory Lib "kernel32" Alias _
    "RtlMoveMemory" (Destination As Any, Source As Any, _
    ByVal length As Long)

Public Declare Function CloseHandle Lib "kernel32.dll" ( _
    ByVal hObject As Long) As Long

Public Declare Function UnmapViewOfFile Lib "kernel32.dll" ( _
    ByVal lpBaseAddress As Any) As Long

要记住的另一件事 - 由于您使用的是网络驱动器，因此您需要确保缓存机制不会干扰对文件的访问。具体来说，您要确保所有客户端都关闭了网络文件缓存。您可能还需要确定性地刷新内存映射，而不是依赖于操作系统（请参阅FlushViewOfFile）。

如何使用VBA中的CopyMemory存储数据并从内存映射文件中获取数据？

1 个答案: