Help with threads

[FISH786]

I am trying to follow this: [Creating Threads using the CreateThread() API](<a href=)[^]"> However I am having an issue, My thread is still running even though the main process id done. What I am trying to achive is a loop to create threads and wait for all the threads to finish the process before I run the same process again. My Issue is I get a message to say my loop is done, however the thread is still running. Could someone please shed some light.

DWORD WINAPI Thread_1(LPVOID lpParam)
{
int a =0;
char Temp[256];
THREADDATA* pData = (THREADDATA*) lpParam;
UINT nEid = pData->nEditId;
CThreadDemoDlg* pDlg = pData->pObjDlg;
for (a = 0;a<20;a++)
{
_itoa_s(a,Temp,sizeof(Temp),10);
pDlg->SetDlgItemText(nEid,Temp);
ProcessMessages();
}
return 0;
}

DWORD WINAPI Thread_2(LPVOID lpParam)
{
int a =0;
char Temp[256];
THREADDATA* pData = (THREADDATA*) lpParam;
UINT nEid = pData->nEditId;
CThreadDemoDlg* pDlg = pData->pObjDlg;
for (a = 0;a<20;a++)
{
_itoa_s(a+1,Temp,sizeof(Temp),10);
pDlg->SetDlgItemText(nEid,Temp);
Sleep(1000);
ProcessMessages();
}
return 0;
}

TD1->pObjDlg = this;
TD2->pObjDlg = this;
TD1->nEditId = IDC_STATIC1;
TD2->nEditId = IDC_STATIC2;

HANDLE hThread_1;
HANDLE hThread_2;

HANDLE Array_Thread[2];

for (x=0 x<10;x++)
{
hThread_1 = CreateThread(NULL,0,Thread_1,TD1,0,NULL);
if (hThread_1 == NULL)
ExitProcess(-1);
hThread_2 = CreateThread(NULL,0,Thread_2,TD2,0,NULL);
if (hThread_2 == NULL)
ExitProcess(-1);
ProcessMessages();
x++;
_itoa_s(f,Temp,sizeof(Temp),10);
SetDlgItemText(IDC_Main,Temp);
Array_Thread[0]= hThread_1;
Array_Thread[1]= hThread_2;

    WaitForMultipleObjects(2,Array\_Thread,TRUE,INFINITE);
    CloseHandle(hThread\_1);
    CloseHandle(hThread\_2);
    //The aim is to wait for the unctions to finish before any of the threads start again

}
MessageBox("Done","Information",MB_OKCANCEL);

I get the messagebox, however the The second thread is still running.

[_Superman_]

How are you validating that the second thread is running?

«_Superman_» I love work. It gives me something to do between weekends.

[Roger Stoltz]

Phweeew... To be honest, there's a lot of things wrong with your code and how you think you should go about multithreading. Let's try and pin-point a few.

• Use AfxBeginThread() when building with MFC framework This must be done to keep the framework happy. Otherwise you'll get into obscure problems that are hard to track down.
• Do NOT touch the GUI from a secondary thread This is very important, especially in MFC since e.g. SetDlgItemText() sends a message to the windows of the control. The difference between sending and posting a message is that sending will block until the message has been processed by the receiving thread. This means that if the thread that "owns" the window doesn't process messages, you'll get a nice little deadlock.
• Worker threads doesn't process messages Your calls to ProcessMessages() are, apart from completely unnecessary, fundamentally wrong. No messages will be sent to your threads. You need to differentiate between so called worker threads that doesn't process messsages and UI-threads.
• Your main thread doesn't process messages After you have called ProcessMessages(), your main thread doesn't process messages any longer. This means that your secondary threads will hang when calling SetDlgItemText() since the receiving window/thread will not consume the message. One way to solve it would be to use ::MsgWaitForMultipleObjects() while waiting for the threads to complete. The correct way would be to return from the function that creates the threads and revert to the window procedure for the main thread. You get into this kind of trouble since you're trying to learn multithreading, but you're using it in a way that contradicts with the reason for having multiple threads since you're still doing things sequentially.

I suspect that the reason why your thread #2 is "still running" when you get the message box is a combination of the above. In other words: your thread #2 hangs because of the call to ::Sleep() since by the time it resumes execution your main thread has stopped processing messages. You should really have a look at the return value from ::WaitForMultipleObjects(). Some words about what you should do.... :-\ Forget about the article you referred to and start here[

[Rajesh R Subramanian]

FISH786 wrote:

CThreadDemoDlg* pDlg = pData->pObjDlg;

I smell MFC?

FISH786 wrote:

hThread_2 = CreateThread(NULL,0,Thread_2,TD2,0,NULL);

And you're calling CreateThread(). First things first[^]

It is a crappy thing, but it's life -^ Carlo Pallini

[FISH786]

Thank you for the feedback. I appreciate the honesty. I will check on the article and work my way from there. thanks a million.

[Roger Stoltz]

Rajesh R Subramanian wrote:

FISH786 wrote:

CThreadDemoDlg* pDlg = pData->pObjDlg;

I smell MFC?

FISH786 wrote:

MessageBox("Done","Information",MB_OKCANCEL);

Calling MessageBox() without a window handle looks very MFC-ish to me, so I guess we are right in our assumptions... ;)

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

[Rajesh R Subramanian]

So, we can confirm the crime. :suss: But, I didn't go that far. I saw the CThreadDemoDlg* on the first few lines and assumed MFC. After all, the user (while sober) cannot come up with a funky name of that sort on his own. :)

It is a crappy thing, but it's life -^ Carlo Pallini

[FISH786]

According to the article. The array I pass of handles to the WaitMultipleObjects should take care of that for me.