CODEWITHSUNDEEP
c++windowswinapi
kernel
kernel

Reputation: 346

Thread Not executing when WaitforMultipleObjects() function is used

I am trying to make a test console application which opens and downloads data from different COM ports using different threads . After downloading data I am using WaitForMutipleObjects() to wait for download to complete from all the threads.

WaitForMultipleObjects(nThreadCount,m_threadHandle,true,INFINITE);

But this is not working , thread is returning without being executed . Here is my thread function.

void* Test::GetData(void *p)
{
   Test *pThis = (Test *)p;
   string strCOMport;
   int nChannelNo,nBaudRate;
   cout<< " Enter COM port "<<endl;
   cin>>strCOMport;
   cout<< " Enter Channel Number"<<endl;
   cin>>nChannelNo;
   cout<< " Enter Baud Rate "<<endl;
   cin>>nBaudRate;

   if(pThis->InitPort(nChannelNo,0x00,(unsigned char *)strCOMport.c_str(),nBaudRate,0x00) == 0x00)
       cout<< "Init port Success"<<endl;
   else
   {
       cout<< "failed";
       return NULL;
   }
   // download
   ExitThread(0);
}

These are the functions which are creating and Waiting for threads respectively

void Test::init()
{
  m_threadHandle[nThreadCount] = CreateThread(NULL,0,(LPTHREAD_START_ROUTINE)GetData,(LPVOID)this,0,&m_dwThreadID[nThreadCount]);
  nThreadCount++;
}

void Test::WaitForThreads()
{
  WaitForMultipleObjects(nThreadCount,m_threadHandle,true,INFINITE);
}

Why is the thread function returning abruptly?

Upvotes: 0

Views: 312

Answers (1)

David Heffernan
David Heffernan

Reputation: 612954

Your thread procedure has the wrong signature. Note that you used a cast to make your code compile. Your code probably originally said:

CreateThread(..., GetData, ...);

And the compiler objected to GetData saying that it was not compatible with a parameter of type LPTHREAD_START_ROUTINE. Unfortunately you chose the wrong solution. Casting it to LPTHREAD_START_ROUTINE does not actually make GetData be a LPTHREAD_START_ROUTINE. It just shuts the compiler up.

CreateThread(..., (LPTHREAD_START_ROUTINE)GetData, ...);

Here, GetData is still not a LPTHREAD_START_ROUTINE, but now the compiler is not able to save you from yourself.

So, you need to declare GetData to have the correct signature.

DWORD WINAPI GetData(LPVOID lpParameter);

And this must be a non-member function, or a static member function.

Once you fix all this you will find that you no longer need to call ExitThread(). You can simply write return 0 from your thread function.

Upvotes: 3

Related Questions