c++ - 命名管道 CreateFile() 返回 INVALID_HANDLE_VALUE，GetLastError() 返回 ERROR_PIPE_BUSY

Question

我已经编写了一个类来处理命名管道连接，如果我创建了一个实例，关闭它，然后尝试创建另一个实例，调用 CreateFile() 返回 INVALID_HANDLE_VALUE，并且 GetLastError() 返回 ERROR_PIPE_BUSY。这里发生了什么？我该怎么做才能确保对 Connect() 的调用成功？

PipeAsync A, B;

A.Connect("\\\\.\\pipe\\test",5000);
A.Close();

cout << GetLastError(); // some random value
B.Connect("\\\\.\\pipe\\test",5000);
cout << GetLastError(); // 231 (ERROR_PIPE_BUSY)
B.Close(); 

这是我对 Connect() 和 Close() 的实现

BOOL PipeAsync::Connect(LPCSTR pszPipeName, DWORD dwTimeout)
{
    this->pszPipeName = pszPipeName;
    this->fExisting = TRUE;
    DWORD dwMode = this->fMessageMode ? PIPE_READMODE_MESSAGE : PIPE_READMODE_BYTE;

    hPipe = CreateFile(
        this->pszPipeName,
        GENERIC_READ | GENERIC_WRITE,
        0,
        NULL,
        OPEN_EXISTING,
        FILE_FLAG_OVERLAPPED,
        NULL);

    if( INVALID_HANDLE_VALUE == hPipe )
        return FALSE; /* set break point here ; breaks here on second call to Connect() */

    if( GetLastError() == ERROR_PIPE_BUSY )
        if(!WaitNamedPipe( this->pszPipeName, dwTimeout ))
            return FALSE; /* set break point here */

    if( !SetNamedPipeHandleState( hPipe, &dwMode, NULL, NULL ) )
        return FALSE; /* set break point here */

    return TRUE;

}

VOID PipeAsync::Close()
{

    if( fExisting )
        DisconnectNamedPipe( hPipe );

    CloseHandle( hPipe );
}

编辑: 我忘了告诉您我是如何得出结论的...我设置了注释中指示的断点。运行时，它会在第一个断点处停止。

编辑:这是我更新的代码

if( INVALID_HANDLE_VALUE == hPipe )
    if( GetLastError() == ERROR_PIPE_BUSY )
    {
        if(!WaitNamedPipe( this->pszPipeName, dwTimeout ))
            return FALSE; /* break-point: breaks here on second call */
    }
    else
        return FALSE; /* break-point /*

现在，WaitNamedPipe() 在第二次调用 Connect() 时返回 false，而 GetLastError() 返回 2，或者 ERROR_FILE_NOT_FOUND ？

Answer 1

来自 Named Pipe Client :

If the pipe exists but all of its instances are busy, CreateFile returns INVALID_HANDLE_VALUE and the GetLastError function returns ERROR_PIPE_BUSY. When this happens, the named pipe client uses the WaitNamedPipe function to wait for an instance of the named pipe to become available.

该链接包含处理 ERROR_PIPE_BUSY 的示例代码。

编辑:

演示在命名管道上接受和连接的小型可编译示例:

const char* const PIPE_NAME = "\\\\.\\pipe\\test";
const int MAX_CONNECTIONS   = 10;

void client_main()
{
    DWORD last_error;
    unsigned int elapsed_seconds       = 0;
    const unsigned int timeout_seconds = 5;

    HANDLE handle = CreateFile(PIPE_NAME,
                               GENERIC_READ | GENERIC_WRITE,
                               0,
                               0,
                               OPEN_EXISTING,
                               FILE_ATTRIBUTE_NORMAL,
                               0);

    while (INVALID_HANDLE_VALUE == handle &&
           elapsed_seconds < timeout_seconds)
    {
        last_error = GetLastError();

        if (last_error != ERROR_PIPE_BUSY)
        {
            break;
        }

        Sleep(1 * 1000);
        elapsed_seconds++;

        handle = CreateFile(PIPE_NAME,
                            GENERIC_READ | GENERIC_WRITE,
                            0,
                            0,
                            OPEN_EXISTING,
                            FILE_ATTRIBUTE_NORMAL,
                            0);
    }

    if (INVALID_HANDLE_VALUE == handle)
    {
        std::cerr << "Failed to connect to pipe " << PIPE_NAME <<
            ": last_error=" << last_error << "\n";
    }
    else
    {
        std::cout << "Connected to pipe " << PIPE_NAME << "\n";
        CloseHandle(handle);
    }
}

HANDLE _get_server_handle()
{
    // Error handling omitted for security descriptor creation.
    SECURITY_DESCRIPTOR sd;
    InitializeSecurityDescriptor(&sd, SECURITY_DESCRIPTOR_REVISION);
    SetSecurityDescriptorDacl(&sd, TRUE, static_cast<PACL>(0), FALSE);

    SECURITY_ATTRIBUTES sa;
    sa.nLength              = sizeof(sa);
    sa.lpSecurityDescriptor = &sd;
    sa.bInheritHandle       = FALSE;

    // Create a bi-directional message pipe.
    HANDLE handle = CreateNamedPipe(PIPE_NAME,
                                    PIPE_ACCESS_DUPLEX,
                                    PIPE_TYPE_MESSAGE       |
                                      PIPE_READMODE_MESSAGE |
                                      PIPE_NOWAIT,
                                    PIPE_UNLIMITED_INSTANCES,
                                    4096,
                                    4096,
                                    0,
                                    &sa);

    if (INVALID_HANDLE_VALUE == handle)
    {
        std::cerr << "Failed to create named pipe handle: last_error=" <<
            GetLastError() << "\n";
    }

    return handle;
}

void server_main()
{
    HANDLE handle = _get_server_handle();

    if (INVALID_HANDLE_VALUE != handle)
    {
        int count = 0;
        while (count < MAX_CONNECTIONS)
        {
            BOOL result = ConnectNamedPipe(handle, 0);

            const DWORD last_error = GetLastError();

            if (ERROR_NO_DATA == last_error)
            {
                count++;
                std::cout << "A client connected and disconnected: count=" <<
                    count << "\n";
                CloseHandle(handle);
                handle = _get_server_handle();
            }
            else if (ERROR_PIPE_CONNECTED == last_error)
            {
                count++;
                std::cout << "A client connected before call to " <<
                    "ConnectNamedPipe(): count=" << count << "\n";
                CloseHandle(handle);
                handle = _get_server_handle();
            }
            else if (ERROR_PIPE_LISTENING != last_error)
            {
                std::cerr << "Failed to wait for connection: last_error=" <<
                    GetLastError() << "\n";
                CloseHandle(handle);
                break;
            }
            Sleep(100);
        }
    }
}

int main(int a_argc, char** a_argv)
{
    if (2 == a_argc)
    {
        if (std::string("client") == *(a_argv + 1))
        {
            for (int i = 0; i < MAX_CONNECTIONS; i++)
            {
                client_main();
            }
        }
        else if (std::string("server") == *(a_argv + 1))
        {
            server_main();
        }
    }
    return 0;
}

首先执行服务器端:

pipetest.exe server

然后在客户端执行:

pipetest.exe client

我无法从发布的代码中判断出问题所在。希望这个小例子能帮助您找到问题所在。