Callback function error in std::async call

Question

Using this code sample to add multithreading callback mechanism for the following code using std::function and std::bind.

void MyClass::afterCompleteCallback(string stsstr)
{
     CString strResult;
     strResult.Format(L"You received: %s", stsstr); //expected "My Output 1"
     GetDlgItem(IDC_STATIC)->SetWindowTextW(strResult);
}

void MyClass::StartMyThread()
{
    auto callback = std::bind(&MyClass::afterCompleteCallback, this, std::placeholders::_1);
    string _data = "My Input 1"
    _aStatus = std::async(std::launch::async, longRunningFunction(callback), data);
}


void MyClass::OnBnClickedButton1()
{
    StartMyThread();
}

I am modifying the longRunningFunction(callback) with

auto _aStatus = std::async(std::launch::async, longRunningFunction(callback), data);

but getting the error no instance of overloaded function matches the argument list error.

My end goal is to pass some str data to thread OnButtonClick() event and get a str result from the thread via callback and update in the MFC TextEdit control. How can I achieve this?

Answer 1

A safe way to accomplish this would be to use sending message(s) from your thread, something like:

void MyClass::longRunningFunction(callback, HWND hWnd)
{
//  longRunning_task
    ::PostMessage(hWnd, WMU_NOTIFYTHREAD, WMU_JOBDONE, 0/*items_received*/);
}

and then:

// CMyDialog implementation

    BEGIN_MESSAGE_MAP(CMyDialog, CDialog)
        //{{AFX_MSG_MAP(CMyDialog)
        //}}AFX_MSG_MAP
        ON_MESSAGE(WMU_NOTIFYTHREADUPDATE, &CMyDialog::OnNotifyThread)
    END_MESSAGE_MAP()

and

LRESULT CMyDialog::OnNotifyThread(WPARAM wParam, LPARAM lParam)
{
    switch (wParam)
    {
    case WMU_JOBDONE:
        CString sText{};
        sText.format(_T("You received: %d"), lParam);
        GetDlgItem(IDC_STATIC)->SetWindowTextW(sText);
        break;
    }

    return 1;
}