C 两个进程之间的命名共享内存

我正在尝试使用文件映射在C中构建一个客户机/服务器，虽然它还处于开发的早期阶段，但我在理解文件映射的确切工作原理时遇到了一些困难

我在我的服务器上创建了一个结构的文件映射，并在上面放置了一些数据，然后我的客户机打开映射文件a读取数据ok。然后，我的客户机写入数据供服务器读取，但服务器无法读取客户机数据，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event，但我认为这不需要它们（是吗？）

她就是我的密码

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);

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：

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

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!!!!!!!!!!"));

---

谢谢

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，要映射的可用地址将用完。把它扔掉。在进入循环之前，应该使用已从第一个

MapViewOfFile（）

获取的

pBuf

指针。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，而是将数据写入本地

HBACKUPSERVICE

变量，而不是映射视图。这就是服务器看不到数据的原因

试试这个：

常见的：

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

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);

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：

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

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

对于跨流程边界的互操作是危险的。想象一下，如果ANSI应用程序尝试与UNICODE应用程序通信，会发生什么情况。他们不会同意您的

szWork

字段的格式，因此也不会同意您的

HBACKUPSERVICE

结构的字节大小。根据您的需要，您应该将

TCHAR

替换为

CHAR

或

WCHAR

，并在两端保持一致。

您确定您的客户实际上写得正确吗？您是否尝试读取刚才写入的内容？是的，客户端写入共享结构可能是缓存的问题，使服务器无法实际重新读取写入的内容。我不这么认为，结构映射到两个进程上的内存，因此理论上，两个进程都应该“看到”工作的相同对象：）谢谢。我害怕使用指针，因为我不知道它们在不同的进程中如何使用，但它完全起作用了。同样感谢您对TCHAR的介绍，但这只是学术性的，我们被要求使用Unicode。如果您被要求使用Unicode，那么您应该使用

WCHAR

，

CreateFileMappingW（）

，

OpenFileMappingW（）

，

wprintf（）

和

StringCchCopyW（）