共享内存----实现进程间通信

C++使用共享内存实现进程间通信

 

　　文件映射是一种实现进程间单向或双向通信的机制。它允许两个或多个本地进程间相互通信。为了共享文件或内存，所有的进程必须使用相同的文件映射的名字或是句柄。

　　为了实现共享文件，第一个进程先调用CreateFile方法。接下来调用CreateFileMapping方法来创建一个文件映射对象。并为文件映射指明一个句柄和名称。由于事件，信号，互斥对象和文件映射等这些内核对象都共享同一个名字空间，所以如果这个名字和其他一个对象的名称重名的话那么将创建失败。

　　为了实现共享内存，进程应首先调用CreateFileMapping函数然后在hFile参数中传入INVALID_HANDLE_VALUE宏来替代句柄。相应的文件映射对象会从系统的分页文件中获得一段内存。如果hFile参数的值是INVALID_HANDLE_VALUE，那么你在调用CreateFileMapping时必须给共享内存指定一个大小值。

　　使用共享内存或文件的进程必须使用MapViewOfFile函数或MapViewOfFileEx函数来创建一个文件视图。

　　下面我们创建一个名称为"Local\SampleMap"的文件映射对象，并将一个字符串写入到文件映射中。

　　我们将创建两个程序，一个是服务程序，一个是客户程序。服务程序负责创建文件映射。

　　服务程序命名为CppFileMappingServer，它的执行过程是

　　1、创建一个特定大小的文件映射对象，名称为“Local\SampleMap”

　　2、将这个对象的文件视图映射到进程的地址空间，然后向视图中写入字符串。

　　接下来执行客户程序CppFileMappingClient，它首先打开这个名称为“Local\SampleMap”的文件映射对象。然后把相同的文件映射视图映射到自己的地址空间中。然后从视图中读取服务进程所写入的数据。

　　Server完整源码：

#pragma region Includes#include <stdio.h>#include <windows.h>#pragma endregion#define MAP_PREFIX          L"Local\\"#define MAP_NAME            L"SampleMap"#define FULL_MAP_NAME       MAP_PREFIX MAP_NAME // Max size of the file mapping object.#define MAP_SIZE            65536 // File offset where the view is to begin.#define VIEW_OFFSET         0 // The number of bytes of a file mapping to map to the view. All bytes of the // view must be within the maximum size of the file mapping object (MAP_SIZE). // If VIEW_SIZE is 0, the mapping extends from the offset (VIEW_OFFSET) to  // the end of the file mapping.#define VIEW_SIZE           1024 // Unicode string message to be written to the mapped view. Its size in byte // must be less than the view size (VIEW_SIZE).#define MESSAGE             L"Message from the first process." int wmain(int argc, wchar_t* argv[]){    HANDLE hMapFile = NULL;    PVOID pView = NULL;     // Create the file mapping object.    hMapFile = CreateFileMapping(        INVALID_HANDLE_VALUE,   // Use paging file - shared memory        NULL,                   // Default security attributes        PAGE_READWRITE,         // Allow read and write access        0,                      // High-order DWORD of file mapping max size        MAP_SIZE,               // Low-order DWORD of file mapping max size        FULL_MAP_NAME           // Name of the file mapping object        );    if (hMapFile == NULL)     {        wprintf(L"CreateFileMapping failed w/err 0x%08lx\n", GetLastError());        goto Cleanup;    }    wprintf(L"The file mapping (%s) is created\n", FULL_MAP_NAME);     // Map a view of the file mapping into the address space of the current     // process.    pView = MapViewOfFile(        hMapFile,               // Handle of the map object        FILE_MAP_ALL_ACCESS,    // Read and write access        0,                      // High-order DWORD of the file offset         VIEW_OFFSET,            // Low-order DWORD of the file offset         VIEW_SIZE               // The number of bytes to map to view        );    if (pView == NULL)    {         wprintf(L"MapViewOfFile failed w/err 0x%08lx\n", GetLastError());         goto Cleanup;    }    wprintf(L"The file view is mapped\n");     // Prepare a message to be written to the view.    PWSTR pszMessage = MESSAGE;    DWORD cbMessage = (wcslen(pszMessage) + 1) * sizeof(*pszMessage);     // Write the message to the view.    memcpy_s(pView, VIEW_SIZE, pszMessage, cbMessage);     wprintf(L"This message is written to the view:\n\"%s\"\n",        pszMessage);     // Wait to clean up resources and stop the process.    wprintf(L"Press ENTER to clean up resources and quit");    getchar(); Cleanup:     if (hMapFile)    {        if (pView)        {            // Unmap the file view.            UnmapViewOfFile(pView);            pView = NULL;        }        // Close the file mapping object.        CloseHandle(hMapFile);        hMapFile = NULL;    }     return 0;}

Client完整源码：

#pragma region Includes#include <stdio.h>#include <windows.h>#pragma endregion#define MAP_PREFIX          L"Local\\"#define MAP_NAME            L"SampleMap"#define FULL_MAP_NAME       MAP_PREFIX MAP_NAME // File offset where the view is to begin.#define VIEW_OFFSET         0 // The number of bytes of a file mapping to map to the view. All bytes of the // view must be within the maximum size of the file mapping object. If // VIEW_SIZE is 0, the mapping extends from the offset (VIEW_OFFSET) to the // end of the file mapping.#define VIEW_SIZE           1024 int wmain(int argc, wchar_t* argv[]){    HANDLE hMapFile = NULL;    PVOID pView = NULL;     // Try to open the named file mapping identified by the map name.    hMapFile = OpenFileMapping(        FILE_MAP_READ,          // Read access        FALSE,                  // Do not inherit the name        FULL_MAP_NAME           // File mapping name         );    if (hMapFile == NULL)     {        wprintf(L"OpenFileMapping failed w/err 0x%08lx\n", GetLastError());        goto Cleanup;    }    wprintf(L"The file mapping (%s) is opened\n", FULL_MAP_NAME);     // Map a view of the file mapping into the address space of the current     // process.    pView = MapViewOfFile(        hMapFile,               // Handle of the map object        FILE_MAP_READ,          // Read access        0,                      // High-order DWORD of the file offset         VIEW_OFFSET,            // Low-order DWORD of the file offset        VIEW_SIZE               // The number of bytes to map to view        );    if (pView == NULL)    {        wprintf(L"MapViewOfFile failed w/err 0x%08lx\n", GetLastError());         goto Cleanup;    }    wprintf(L"The file view is mapped\n");     // Read and display the content in view.    wprintf(L"Read from the file mapping:\n\"%s\"\n", (PWSTR)pView);     // Wait to clean up resources and stop the process.    wprintf(L"Press ENTER to clean up resources and quit");    getchar(); Cleanup:     if (hMapFile)    {        if (pView)        {            // Unmap the file view.            UnmapViewOfFile(pView);            pView = NULL;        }        // Close the file mapping object.        CloseHandle(hMapFile);        hMapFile = NULL;    }     return 0;}

运行效果：

　　Server

　　Client