Problem with Win32 Threads

[kikoso]

Hello all, I´m trying to multithread an application by using CreateThread function. So far I´ve done the following:

//Here I initialize the Thread
LPDWORD iID;
HANDLE hThread; // array of thread handles
hThread = CreateThread (
0, // Security attributes
0, // Stack size
(LPTHREAD_START_ROUTINE)OpenCVWin32::Form1::Threadi,
NULL,
CREATE_SUSPENDED,
iID);
}

//Called function
static DWORD WINAPI Threadi()
{
System::Windows::Forms::MessageBox::Show("Hi there!");
return 0;
}

When I launch the application, the thread is not created, as I cannot go inside the Threadi function. I´m right now using VC++ 2008. Does anyone has a suggestion on why this could be happening? Thanks

[HimanshuJoshi]

kikoso wrote:

CREATE_SUSPENDED,

This is the problem. If you use this attribute then the thread is created in suspended state. More Info Here[^] If you want the thread to start as soon as you launch the application, don't create a thread in suspended state. If you want to create in suspended state, then you can use ResumeThread() function.

[User 3919723]

LPTHREAD_START_ROUTINE is defined as: typedef DWORD (WINAPI *PTHREAD_START_ROUTINE)( LPVOID lpThreadParameter ); typedef PTHREAD_START_ROUTINE LPTHREAD_START_ROUTINE; so, your thread function is to be: static DWORD WINAPI Threadi(LPVOID lpThreadParameter) { System::Windows::Forms::MessageBox::Show("Hi there!"); return 0; }

[kikoso]

Hello! Thank you! I didn´t though that passing the parameters will be compulsory. But nevermind, I put it on my code.

[kikoso]

Thank you HimanshuJoshi. I was reading in zig-zag the doc, so I didn´t realize about it. I still have some problems. After changing it, I have a problem accessing the memory. This is the error I got (after using 0 instead of CREATE_SUSPENDED,: Unhandled exception at 0x003628c2 in OpenCV Win32.exe: 0xC0000005: Access violation reading at position 0x0000000c. I´ve been thinking about sending the 3 parameter as (LPTHREAD_START_ROUTINE)&OpenCVWin32::Form1::Threadi, But I got a different error: error C3374: Address of "OpenCVWin32:: Form1:: Threadi" can only be adopted if a delegate instance is created. I will appreciate any suggestions. Thank you :)

[Rajesh R Subramanian]

If you're using MFC, you *must* use AfxBeginThread to begin a worker thread. If you are using Win32, you should be using _beginthreadex to create a thread. CreateThread is an API and that will even create a thread if you're linking to the single threaded version of the CRT (which will inevitably lead to disaster). If you're writing managed code, take a look at Thread.Start method in the documentation. Basically, I want to emphasise that there's no sane reason or excuse to use CreateThread from your code. There are safer and sane alternatives.

“Follow your bliss.” – Joseph Campbell

[kikoso]

Hello, I finally found the problem. The code for the Thread Function was inside the ref class, so that made it managed code. I finally put outside it, and now is working fine :) Thank you.