c++ - CreateFileMapping、MapViewOfFile、处理泄漏的 c++

Question

背景:我正在尝试创建一个可以被多个进程访问的内存映射文件。在下面的代码中，我只放入了与我目前必须使事情变得更简单的问题有关的代码。根据 msdn，我应该能够创建一个文件映射，映射文件的 View 并关闭我从 CreateFileMapping 收到的句柄，而 MapViewOfFile 将使我的 FileMap 保持事件状态。在我 UnmapViewOfFile 之前，FileMap 应该仍然可以访问。

MSDN: CreateFileMapping function

Mapped views of a file mapping object maintain internal references to the object, and a file mapping object does not close until all references to it are released. Therefore, to fully close a file mapping object, an application must unmap all mapped views of the file mapping object by calling UnmapViewOfFile and close the file mapping object handle by calling CloseHandle. These functions can be called in any order.

问题: 在成功映射文件 View 然后关闭 CreateFileMapping 接收到的句柄后，FileMap 不再存在(它应该仍然存在)并且我的 MemMapFileReader 能够创建一个新映射错误 0。(当它应该收到错误 183“已经存在”时)

错误的解决方案:不关闭句柄允许 MemMapFileReader 程序访问它，但会导致 MemMapFileCreator 中的句柄泄漏，因为在进程关闭之前句柄永远不会关闭。

问题我错过了什么或做错了什么？

内存映射文件创建器

#include "stdafx.h"


#include <windows.h>
#include <stdio.h>
#include <conio.h>
#include <tchar.h>
#include <iostream>
#define BUF_SIZE 256
TCHAR szName[] = TEXT("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

DWORD lastError = GetLastError();
if (hMapFile == NULL)
{
    _tprintf(TEXT("Could not create file mapping object (%d).\n"),
        GetLastError());
    std::cin.get();
    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);

    std::cin.get();
    return 1;
}


CopyMemory((PVOID)pBuf, szMsg, (_tcslen(szMsg) * sizeof(TCHAR)));

CloseHandle(hMapFile);

_getch();


UnmapViewOfFile(pBuf);
return 0;
}

内存映射文件读取器

#include "stdafx.h"
#include <windows.h>
#include <stdio.h>
#include <conio.h>
#include <tchar.h>
#include <iostream>
#pragma comment(lib, "user32.lib")

#define BUF_SIZE 256
TCHAR szName[] = TEXT("MyFileMappingObject");

int _tmain()
{
HANDLE hMapFile;
LPCTSTR pBuf;

hMapFile = CreateFileMapping(
    INVALID_HANDLE_VALUE,
    NULL,
    PAGE_READWRITE,   // read/write access
    0,
    BUF_SIZE,
    szName);               // name of mapping object
DWORD lastError = GetLastError();
if (hMapFile == NULL)
{
    _tprintf(TEXT("Could not open file mapping object (%d).\n"),
        GetLastError());
    std::cin.get();
    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);

    std::cin.get();
    return 1;
}

MessageBox(NULL, pBuf, TEXT("Process2"), MB_OK);

UnmapViewOfFile(pBuf);

CloseHandle(hMapFile);

std::cin.get();
return 0;
}

Answer 1

来自 MSDN:

Mapped views of a file mapping object maintain internal references to the object, and a file mapping object does not close until all references to it are released. Therefore, to fully close a file mapping object, an application must unmap all mapped views of the file mapping object by calling UnmapViewOfFile and close the file mapping object handle by calling CloseHandle. These functions can be called in any order.

CreateFileMapping 文档指出，要完全关闭文件，必须关闭所有句柄，顺序无关紧要。此逻辑不可逆:您不能关闭一个句柄并期望使用其他句柄，就好像文件映射没有“关闭”一样。

换句话说，这意味着要清理文件映射，您需要按任意顺序关闭所有句柄。但是，您不能关闭底层文件映射对象并仍然使用依赖于它的 View 。