4

我正在尝试使用文件映射在 C 中构建客户端/服务器，它仍然处于开发的早期阶段，但我在理解文件映射的工作原理时遇到了一些麻烦。

我在我的服务器上创建了一个结构的文件映射并将一些数据放在上面，然后我的客户端打开文件映射并读取数据。然后我的客户端写入数据供服务器读取，但服务器无法读取客户端数据，我不明白为什么，因为文件映射应该在两个进程之间同步。在这个阶段我仍然没有使用事件，但我认为不需要它们来工作（是吗？）

她是我的密码。

服务器：

struct _HBACKUPSERVICE{
    DWORD           dwServerProcessID;
    TCHAR           szWork[MAX_PATH];
    HANDLE          hMapFile;
};

PHBACKUPSERVICE pBuf = NULL;
HANDLE hMapFile;

hMapFile = CreateFileMapping(
    INVALID_HANDLE_VALUE,    // use paging file
    NULL,                    // default security
    PAGE_READWRITE,          // read/write access
    0,                       // maximum object size (high-order DWORD)
    sizeof(HBACKUPSERVICE),  // maximum object size (low-order DWORD)
    _T("MyService"));        // name of mapping object

if (/*phBackupService->*/hMapFile == NULL){
    _tprintf(TEXT("Could not create file mapping object (%d).\n"),
        GetLastError());
    return *pBuf;
}

pBuf = (PHBACKUPSERVICE)MapViewOfFile(
    hMapFile,               // handle to map object
    FILE_MAP_ALL_ACCESS,    // read/write permission
    0,
    0,
    sizeof(HBACKUPSERVICE));

if (pBuf == NULL){
    _tprintf(TEXT("Could not map view of file (%d).\n"),
        GetLastError());
    return *pBuf;
}


// Populate backup service structure
pBuf->hMapFile = hMapFile;
pBuf->dwServerProcessID = GetCurrentProcessId();

// Wait for client
do{
    _tprintf(_T("\nServer: Waiting for work."));
    pBuf = (PHBACKUPSERVICE)MapViewOfFile(
        _BackupService.hMapFile,    // handle to map object
        FILE_MAP_ALL_ACCESS,        // read/write permission
        0,
        0,
        sizeof(HBACKUPSERVICE));
    if (StringCbLength(pBuf->szWork, 1 * sizeof(TCHAR), NULL) == S_OK){ Sleep(500); }
} while (StringCbLength(pBuf->szWork, 1 * sizeof(TCHAR), NULL) == S_OK); // ERROR: pBuf->szWork is always empty...

_tprintf(_T("Work from client: %s"), pBuf->szWork);

客户：

HBACKUPSERVICE _BackupService;
HANDLE hMapFile;

hMapFile = OpenFileMapping(
    FILE_MAP_ALL_ACCESS,   // read/write access
    FALSE,                 // do not inherit the name
    _T("MyService"));          // name of mapping object

if (hMapFile == NULL)
{
    _tprintf(TEXT("Could not open file mapping object (%d).\n"),
        GetLastError());
}

BackupService= (PHBACKUPSERVICE)MapViewOfFile(
    hMapFile,               // handle to map object
    FILE_MAP_ALL_ACCESS,    // read/write permission
    0,
    0,
    sizeof(HBACKUPSERVICE));

_tprintf(_T("Server process id: %d"), _BackupService.dwServerProcessID);
_tprintf(_T("send work to server"));
StringCchCopy(_BackupService.szWork, STRSAFE_MAX_CCH, _T("Do work for me!!!!!!!!!!")); //ERROR: the server never sees this

谢谢！

4

1 回答 1

2

您的服务器正在其读取循环中调用MapViewOfFile()，因此您正在映射越来越多的指针而不是取消映射它们。最终，您将用完可用的映射地址。摆脱它。在进入循环之前，您应该使用pBuf从第一个获得的指针。MapViewOfFile()您只需映射视图一次。

您的客户端根本没有将数据写入映射视图，而是写入局部HBACKUPSERVICE变量而不是映射视图。这就是服务器看不到数据的原因。

尝试这个：

常见的：

typedef struct _HBACKUPSERVICE {
    DWORD           dwServerProcessID;
    TCHAR           szWork[MAX_PATH];
    HANDLE          hMapFile;
} HBACKUPSERVICE, *PHBACKUPSERVICE;

服务器：

PHBACKUPSERVICE pBuf = NULL;
HANDLE hMapFile;

hMapFile = CreateFileMapping(
    INVALID_HANDLE_VALUE,    // use paging file
    NULL,                    // default security
    PAGE_READWRITE,          // read/write access
    0,                       // maximum object size (high-order DWORD)
    sizeof(HBACKUPSERVICE),  // maximum object size (low-order DWORD)
    _T("MyService"));        // name of mapping object

if (hMapFile == NULL){
    _tprintf(TEXT("Could not create file mapping object (%d).\n"),
        GetLastError());
    return NULL;
}

pBuf = (PHBACKUPSERVICE)MapViewOfFile(
    hMapFile,               // handle to map object
    FILE_MAP_ALL_ACCESS,    // read/write permission
    0,
    0,
    sizeof(HBACKUPSERVICE));

if (pBuf == NULL){
    _tprintf(TEXT("Could not map view of file (%d).\n"),
        GetLastError());
    return NULL;
}

// Populate backup service structure
pBuf->hMapFile = hMapFile;
pBuf->dwServerProcessID = GetCurrentProcessId();
ZeroMemory(pBuf->szWork, sizeof(pBuf->szWork));

// Wait for client
_tprintf(_T("\nServer: Waiting for work."));
while (pBuf->szWork[0] == 0){ Sleep(500); }

_tprintf(_T("Work from client: %s"), pBuf->szWork);

客户：

PHBACKUPSERVICE BackupService = NULL;
HANDLE hMapFile;

hMapFile = OpenFileMapping(
    FILE_MAP_ALL_ACCESS,   // read/write access
    FALSE,                 // do not inherit the name
    _T("MyService"));          // name of mapping object

if (hMapFile == NULL)
{
    _tprintf(TEXT("Could not open file mapping object (%d).\n"),
        GetLastError());
}

BackupService = (PHBACKUPSERVICE)MapViewOfFile(
    hMapFile,               // handle to map object
    FILE_MAP_ALL_ACCESS,    // read/write permission
    0,
    0,
    sizeof(HBACKUPSERVICE));

if (BackupService == NULL){
    _tprintf(TEXT("Could not map view of file (%d).\n"),
        GetLastError());
}

_tprintf(_T("Server process id: %d"), BackupService->dwServerProcessID);
_tprintf(_T("send work to server"));
StringCchCopy(BackupService->szWork, MAX_PATH, _T("Do work for me!!!!!!!!!!"));

最后，TCHAR对于跨进程边界的互操作是危险的。想象一下，如果一个 ANSI 应用程序试图与一个 UNICODE 应用程序通信会发生什么。他们不会就您的szWork字段格式达成一致，因此不会就您的HBACKUPSERVICE结构的字节大小达成一致。您应该根据需要替换TCHAR为CHARor WCHAR，并在两端保持一致。

于 2014-07-12T17:22:57.253 回答