Multithreaded App

Manmohan29

I am new to multithreading and my application doesnot compile. It is a Dialog Based Applicationin MFC with only one ButtonCtrl Here's the code

UINT ThreadFunc(LPVOID pParam)
{
MessageBox("Thread Started");
return 0;
}

void CAppDlg::OnButtonClkRunThread()
{
AfxBeginThread(ThreadFunc, this);
}

Where am I going wrong?

Manmohan Bishnoi

CPallini

Usually compiler errors are pretty informative, so have a look at it. I guess the error occurs in

Manmohan29 wrote:

MessageBox("Thread Started");

:)

If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler. -- Alfonso the Wise, 13th Century King of Castile.
This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong. -- Iain Clarke
[My articles]

Game point

try this ...

UINT ThreadFunc (LPVOID lpParam)
{
::MessageBox(0,L"Thread Started",L"",1);
return 0;
}

void CAppDlg::OnButtonClkRunThread()
{
::AfxBeginThread (ThreadFunc,this);
}

Rajesh R Subramanian

Manmohan29 wrote:

doesnot compile

And what does the compiler say? Be specific. To add to it,

Manmohan29 wrote:

UINT ThreadFunc(LPVOID pParam) { MessageBox("Thread Started"); //----> BAD idea! return 0; } void CAppDlg::OnButtonClkRunThread() { AfxBeginThread(ThreadFunc, this); }

Because if your main thread becomes busy into something, the newly spawned thread as well would block for displaying the message. This is because you are using a function (MessageBox from MFC) that would make use of the default message pump of your application. In other words, if you add a Sleep(3000); after AfxBeginThread, the message from your thread would probably be displayed after this sleep period only! I see you're just starting to learn, but threading has such "gotchas", that you'll learn along the way. Lesson learned today: It isn't a great idea to use something within a worker thread, that may in turn use the default message pump of the application (in a blocking fashion). :)

“Follow your bliss.” – Joseph Campbell

Manmohan29

NEW CODE :- UINT CThreadDlg::ThreadFunc(LPVOID pParam) { return 0; } void CThreadDlg::OnBnClickedBthread() { // TODO: Add your control notification handler code here AfxBeginThread(ThreadFunc, this); } ERROR :- ------ Build started: Project: Thread, Configuration: Debug Win32 ------ Compiling... ThreadDlg.cpp d:\manmohan\visual c++\thread\thread\threaddlg.cpp(162) : error C3867: 'CThreadDlg::ThreadFunc': function call missing argument list; use '&CThreadDlg::ThreadFunc' to create a pointer to member Build log was saved at "file://d:\Manmohan\Visual C++\Thread\Thread\Debug\BuildLog.htm" Thread - 1 error(s), 0 warning(s) ========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========

Manmohan Bishnoi

Rajesh R Subramanian

Manmohan29 wrote:

UINT CThreadDlg::ThreadFunc(LPVOID pParam) //---> Here is the problem! { return 0; } void CThreadDlg::OnBnClickedBthread() { // TODO: Add your control notification handler code here AfxBeginThread(ThreadFunc, this); }

The thread function should be a global function (not a member function of any class), or it must be a static member function of any class. Try this instead: in your header file:

static UINT CThreadDlg::ThreadFunc(LPVOID pParam);

in the source file:

/*static*/ UINT CThreadDlg::ThreadFunc(LPVOID pParam){
OutputDebugString(_T("*********** Entered thread function ***********\n"));
return false;
}

Watch the output window of your debugger to see the text printed from your thread.

“Follow your bliss.” – Joseph Campbell

Roger Stoltz

Manmohan29 wrote:

UINT CThreadDlg::ThreadFunc(LPVOID pParam)

This member has to be declared as 'static'.

"It's supposed to be hard, otherwise anybody could do it!" - selfquote
"High speed never compensates for wrong direction!" - unknown

Rajesh R Subramanian

My previous answer to you is updated after you edited your post to include the code. Check it.

“Follow your bliss.” – Joseph Campbell

Manmohan29

Thanks, It works great.

Manmohan Bishnoi