Can't we use threads inside the member function of class?

Question

This is mine base class

class IDialysisConnector
    {
    public:
    HANDLE threadHandle_;   
    virtual int ConnectToMachine();  //This will make socket connection with the machine.
    virtual void WINAPI ServerConnectThread(LPVOID lpdwThreadParam)=0;
    };

Another class

class A:public IDialysisConnector
{

int ConnectToMachine()
{

    int conResult,iResult;;
    struct addrinfo           *result = NULL,*ptr = NULL;

    u_long iMode = 0;
    DWORD nTimeout = 5000; // 5 seconds
    int port=22;
    WSADATA wsaData;

    // Initialize Winsock

    iResult = WSAStartup(MAKEWORD(2,2), &wsaData);
    if (iResult != 0) 
    {
        printf("WSAStartup failed with error: %d\n", iResult);

    }

    ZeroMemory( &addr_, sizeof(addr_) );
    addr_.ai_family = AF_UNSPEC;
    addr_.ai_socktype = SOCK_STREAM;
    addr_.ai_protocol = IPPROTO_TCP;

    // Resolve the server address and port
    conResult = getaddrinfo("192.168.15.168", (PCSTR)22, &addr_, &result);
    if ( conResult != 0 ) {
        printf("getaddrinfo failed with error: %d\n", conResult);
        WSACleanup();
        return 1;
    }

    // Attempt to connect to an address until one succeeds
    for(ptr=result; ptr != NULL ;ptr=ptr->ai_next) {

        // Create a SOCKET for connecting to server
        sock_ = socket(ptr->ai_family, ptr->ai_socktype, 
            ptr->ai_protocol);
        if (sock_ == INVALID_SOCKET) {
            printf("socket failed with error: %ld\n", WSAGetLastError());
            WSACleanup();
            return 1;
        }
            conResult = ioctlsocket(sock_, FIONBIO, &iMode);
        if (conResult != NO_ERROR)
            printf("ioctlsocket failed with error: %ld\n", conResult);


        conResult = setsockopt(sock_, SOL_SOCKET, SO_RCVTIMEO, (const char*)&nTimeout, sizeof(DWORD));
        if (conResult != NO_ERROR)
        {
            printf("\nSetsocopt fail with error :%d\n",WSAGetLastError());

            return 0;
        }


        // Connect to server.
        conResult = connect(sock_, ptr->ai_addr, (int)ptr->ai_addrlen);
        if (conResult == SOCKET_ERROR) {
            closesocket(sock_);
            sock_ = INVALID_SOCKET;
            continue;
        }
        break;
    }

    freeaddrinfo(result);

    if (sock_ == INVALID_SOCKET) {
        printf("Unable to connect to server!\n");
        WSACleanup();
        return 1;
    }
    DWORD dwThreadId;
    //threadHandle_=CreateThread(NULL,0,(LPTHREAD_START_ROUTINE)ServerConnectThread,this,0,&dwThreadId);
        threadHandle_=CreateThread(NULL,0,(LPTHREAD_START_ROUTINE)ThreadFunc,this,0,&dwThreadId);
   void WINAPI IDialysisConnector::ServerConnectThread(LPVOID lpdwThreadParam)
    {
SOCKET ThreadSocket = INVALID_SOCKET;
    ThreadSocket=(SOCKET)lpdwThreadParam;
    while(1)
    {
        SendRequest(ThreadSocket);
        ReceiveResponse(ThreadSocket);
        Sleep(10000);
    }
        }

static UINT ThreadFunc(LPVOID param) {
IDialysisConnector* obj = (IDialysisConnector*)param;
obj->ServerConnectThread(); // call the member function
// to do the work in our new thread }

}

}

I did like this too but same error

threadHandle_=CreateThread(NULL,0, (LPTHREAD_START_ROUTINE)IDialysisConnector::ServerConnectThread,(LPVOID)sock_,0,&dwThreadId);

I am getting an error that is

" error C2440: 'type cast' : cannot convert from 'overloaded-function' to 'LPTHREAD_START_ROUTINE'"

One of your problems is that you have a function nested directly inside a function. That isn't legal. — Ben Voigt, Oct 11 '12 at 13:46
It also scares me that an inexperienced programmer is working on what appears to be medical software. — Ben Voigt, Oct 11 '12 at 13:47
@BenVoigt, good catch, I was about to point that out, that's a major syntax error. — Brady, Oct 11 '12 at 13:47
@BenVoigt Good point sir but is an sample and you are correct am not experienced — Dany, Oct 11 '12 at 14:04
You updated the code but you *still* have a function nested directly inside another function. The compiler won't be able to make any sense of your code, I'm surprised it gave you as useful an error message as this. — Ben Voigt, Oct 11 '12 at 15:28

nos · Answer 1 · 2012-10-11T13:54:07.030

4

No, CreateThread expects a plain function pointer, which is quite different from a pointer to a non-static C++ member function.

You have to create a normal function for the function you give CreateThread. That function can act as a trampoline back to the C++ world, e.g.

static UINT WINAPI ThreadFunc(LPVOID param)
{
   IDialysisConnector* obj = (IDialysisConnector*)param;
   obj->ServerConnectThread(); // call the member function
                               // to do the work in our new thread
}

Then your ConnectToMachine becomes:

int ConnectToMachine()
{
    DWORD dwThreadId;
    //give 'this' as the thread param to ThreadFunc
    threadHandle_=CreateThread(NULL,0, (LPTHREAD_START_ROUTINE)ThreadFunc,(LPVOID)this,0,&dwThreadId);
}

edited Oct 11 '12 at 13:54

answered Oct 11 '12 at 13:46

nos

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A static class function works OK whenever I've tried it. Passing 'this' as an explicit parameter then allows the calling of member functions. – Martin James Oct 11 '12 at 13:48
@nos thanks for the answer sir i updated my code as you can see i am expecting a socket as paramer in ServerConnectThread that i pass to my send and recv function,can you please update your solution accordingly – Dany Oct 11 '12 at 14:03
1

@Dany: Put the socket handle in a member variable. Once you pass the `this` pointer to the function, you also have access to all member variables. – Ben Voigt Oct 11 '12 at 15:29
@BenVoigt i also got the same problem i have declare SOCKET sock_ as an public member of the class,now how can i access the socket i mean how to give to ServerConnectThread() – Harry Oct 11 '12 at 17:46
@Harry: The way nos showed you gives the entire class instance to `ServerConnectThread` (it's a non-static member function). So use the `this` pointer from inside, maybe implicitly. – Ben Voigt Oct 11 '12 at 22:40
@Harry The code I showed ends up calling the member function `obj->ServerConnectThread()`, so inside the `ServerConnectThread()` function you simply do `this->my_socket`. And ofcourse, `this` isn't even needed, so if you did make your socket a member variable, you just access it as `my_socket` – nos Oct 11 '12 at 23:26
@Dany Your edited code which you claim fails is wrong, you have this code: `CreateThread(NULL,0, (LPTHREAD_START_ROUTINE)IDialysisConnector::ServerConnectThread,(LPVOID)sock_,0,&dwThreadId);` Which is not what I posted. You _have_ to place `sock_` in a member variable of your `IDIalysisConnectior` class, and you have to do : `CreateThread(NULL,0, (LPTHREAD_START_ROUTINE)ThreadFunc,(LPVOID)this,0,&dwThreadId);` – nos Oct 11 '12 at 23:29

score 0 · Answer 2 · answered Oct 11 '12 at 13:44

A non-static member function can only be called on an object. That's why its type is pointer-to-member-function and not pointer-to-function. CreateThread expects a pointer to function, and you can't give it a pointer to member function instead.

Some folks will advise you to make it a static member function; that's usually okay, but I'm skeptical of design changes that are made only to make implementation easier. If it's a non-static member function, then, presumably, there's a reason for it to be a non-static member function.

You can write a function that does the appropriate call:

void callback(void*p) {
    (IDialysisConnector*p)->ServerConnectThread();
}

and pass that as the thread function, with the address of the appropriate object as the data pointer in the call to CreateThread.

Yes, but this callback helper should probably be the non-static member function you just expressed skepticism about, and it should have a useful name such as `ServerConnectThreadShim`. — Ben Voigt, Oct 11 '12 at 13:48
@BenVoigt - I did **not** express skepticism about a using a static member function. I expressed skepticism about **advising** someone to change a non-static member function into a static one just so it could be passed to `CreateThread` without knowing details of the design. — Pete Becker, Oct 11 '12 at 13:54

Can't we use threads inside the member function of class?

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