我有可能误解了这个问题，所以请多多包涵。我已经决定使用一些工作代码更容易在评论中更清楚地显示我所说的内容。@OP，也许从这里您可以进一步澄清这是否不能解决您的问题？
因此，我采用了 MSFT 提供的示例代码并一起破解来演示我在说什么（所以代码本质上是 MS 示例代码）。
https://msdn.microsoft.com/en-us/library/windows/desktop/aa366551(v=vs.85).aspx
您可以使用 2 个项目创建 VS 解决方案，这是项目/流程 A 的代码：
#include <windows.h>
#include <stdio.h>
#include <conio.h>
#include <tchar.h>
#define BUF_SIZE 256
TCHAR szName[] = TEXT("Global\\MyFileMappingObject");
TCHAR szMsg[] = TEXT("Message from first process.");
int _tmain()
{
HANDLE hMapFile;
LPCTSTR pBuf;
hMapFile = CreateFileMapping(
INVALID_HANDLE_VALUE, // use paging file
NULL, // default security
PAGE_READWRITE, // read/write access
0, // maximum object size (high-order DWORD)
BUF_SIZE, // maximum object size (low-order DWORD)
szName); // name of mapping object
if (hMapFile == NULL)
{
_tprintf(TEXT("Could not create file mapping object (%d).\n"),
GetLastError());
return 1;
}
pBuf = (LPTSTR)MapViewOfFile(hMapFile, // handle to map object
FILE_MAP_ALL_ACCESS, // read/write permission
0,
0,
BUF_SIZE);
if (pBuf == NULL)
{
_tprintf(TEXT("Could not map view of file (%d).\n"),
GetLastError());
CloseHandle(hMapFile);
return 1;
}
CopyMemory((PVOID)pBuf, szMsg, (_tcslen(szMsg) * sizeof(TCHAR)));
_getch();
UnmapViewOfFile(pBuf);
CloseHandle(hMapFile);
return 0;
}
现在这是第二个项目/流程 B 的一些修改代码。请参阅此内容以供参考：https ://msdn.microsoft.com/en-us/library/windows/desktop/aa366548(v=vs.85).aspx
#include <windows.h>
#include <stdio.h>
#include <conio.h>
#include <tchar.h>
#pragma comment(lib, "user32.lib")
#define BUF_SIZE 256
TCHAR szName[] = TEXT("Global\\MyFileMappingObject");
int mapDataAtOffset(DWORD offset, size_t bytesToRead, LPVOID* outData, LPVOID* outMapAddress);
int _tmain()
{
LPCTSTR pBuf;
LPVOID outMapAddress = nullptr;
LPVOID outMapAddress2 = nullptr;
auto ret = mapDataAtOffset(0, 8, (LPVOID*)&pBuf, &outMapAddress);
MessageBox(NULL, pBuf, TEXT("Process2"), MB_OK);
ret = mapDataAtOffset(8, 8, (LPVOID*)&pBuf, &outMapAddress2);
MessageBox(NULL, pBuf, TEXT("Process2"), MB_OK);
if(outMapAddress)UnmapViewOfFile(outMapAddress);
if (outMapAddress2)UnmapViewOfFile(outMapAddress2);
return 0;
}
int mapDataAtOffset(DWORD offset, size_t bytesToRead, LPVOID* outData, LPVOID* outMapAddress) {
HANDLE hMapFile; // handle for the file's memory-mapped region
BOOL bFlag; // a result holder
DWORD dBytesWritten; // number of bytes written
DWORD dwFileMapSize; // size of the file mapping
DWORD dwMapViewSize; // the size of the view
DWORD dwFileMapStart; // where to start the file map view
DWORD dwSysGran; // system allocation granularity
SYSTEM_INFO SysInfo; // system information; used to get granularity
LPVOID lpMapAddress; // pointer to the base address of the
// memory-mapped region
char * pData; // pointer to the data
int i; // loop counter
int iData; // on success contains the first int of data
int iViewDelta; // the offset into the view where the data
//shows up
DWORD FILE_MAP_START = offset;
// Get the system allocation granularity.
GetSystemInfo(&SysInfo);
dwSysGran = SysInfo.dwAllocationGranularity;
// Now calculate a few variables. Calculate the file offsets as
// 64-bit values, and then get the low-order 32 bits for the
// function calls.
// To calculate where to start the file mapping, round down the
// offset of the data into the file to the nearest multiple of the
// system allocation granularity.
dwFileMapStart = (FILE_MAP_START / dwSysGran) * dwSysGran;
_tprintf(TEXT("The file map view starts at %ld bytes into the file.\n"),
dwFileMapStart);
// Calculate the size of the file mapping view.
dwMapViewSize = (FILE_MAP_START % dwSysGran) + bytesToRead;
_tprintf(TEXT("The file map view is %ld bytes large.\n"),
dwMapViewSize);
// How large will the file mapping object be?
dwFileMapSize = FILE_MAP_START + bytesToRead;
_tprintf(TEXT("The file mapping object is %ld bytes large.\n"),
dwFileMapSize);
// The data of interest isn't at the beginning of the
// view, so determine how far into the view to set the pointer.
iViewDelta = FILE_MAP_START - dwFileMapStart;
_tprintf(TEXT("The data is %d bytes into the view.\n"),
iViewDelta);
hMapFile = OpenFileMapping(
FILE_MAP_ALL_ACCESS, // read/write access
FALSE, // do not inherit the name
szName); // name of mapping object
if (hMapFile == NULL)
{
_tprintf(TEXT("Could not open file mapping object (%d).\n"),
GetLastError());
return 1;
}
// Map the view and test the results.
lpMapAddress = MapViewOfFile(hMapFile, // handle to
// mapping object
FILE_MAP_ALL_ACCESS, // read/write
0, // high-order 32
// bits of file
// offset
dwFileMapStart, // low-order 32
// bits of file
// offset
dwMapViewSize); // number of bytes
// to map
if (lpMapAddress == NULL)
{
_tprintf(TEXT("lpMapAddress is NULL: last error: %d\n"), GetLastError());
return 3;
}
// Calculate the pointer to the data.
pData = (char *)lpMapAddress + iViewDelta;
*outData = pData;
*outMapAddress = lpMapAddress;
CloseHandle(hMapFile); // close the file mapping object, doesn't matter as long as view is still mapped
return 0;
}
所以回答你的问题
在没有首先取消映射 pData 的情况下再次调用 MapViewOfFile 是否可以接受？
上面的例子实现了这一点。除非我误解了您的查询，在这种情况下，如果您能澄清一下，那就太好了。