C / C++ / MFC

29-Apr-09 16:59

Hi all,

I am having a c++ file which is used to create mexfunction DLL that can be used to call a function from Matlab through dll. This is used to compute some mathematical calculations on a big matirx and for this I do it in two parallel threads each doing half matrix. At the end I combine both to generate full resultant matrix. For this, I create two different threads as follows-

HANDLE thd_handle[2];
DWORD WINAPI GenerateThread0(LPVOID param);
DWORD WINAPI GenerateThread1(LPVOID param);
void CreateResult0();
void CreateResult1();

void mexFunction(...mex function params....)
{
// do necessary variable declarations
// create two threads
thd_handle[0] = CreateThread(NULL,GenerateThread0, NULL, 0, NULL);
thd_handle[1] = CreateThread(NULL,GenerateThread1, NULL, 0, NULL);
WaitForMultipleObjects(2,thd_handle,true,INFINITE);
// prepare result
// return result to matlab
}
DWORD WINAPI GenerateThread0(LPVOID param)
{
CreateResult0();
return 0;
}
DWORD WINAPI GenerateThread1(LPVOID param)
{
CreateResult1();
return 0;
}
void CreateResult0()
{
//do some computations
}
void CreateResult1()
{
//do some computations
}

Everything is fine and good while doing as above and I used this for a long time without any problems. Now I am planning to make this more efficient by making it multithreading adaptable to the processor on which it runs. I have couple of systems which are like 4core/8core and would like to create threads dynamically. I came up with the following idea and implemented it and guess what it gives fatal errors while running and I highly suspect the way I am creating multiple threads.

HANDLE *thd_handle;
DWORD WINAPI GenerateThread(LPVOID param);
void CreateResult(unsigned int idx);

void mexFunction(...mexfunctionparams...)
{
//read in input params
//find (#processors*#logicalprocs*#coresperproc)=m_nThreads;
thd_handle = new HANDLE[m_nThreads-1];
//CreateThreads
for (unsigned int i=0; i < m_nThreads-1; i++ )
thd_handle[i] = CreateThread(NULL, GenerateThread, &i, 0, NULL);
WaitForMultipleObjects(m_nThreads-1,thd_handle, true,infinite);
//prepare result
//return result to matlab
}
DWORD WINAPI GenerateThread(LPVOID param)
{
DWORD iter = *(DWORD*)param;
CreateResult(iter);
retrun 0;
}
void CreateResult(unsigned int idx)
{
//compute result for this matrix size depending on idx
}

if I use the dll generated from this code, the program crashes... am I doing something fundamentally wrong here?? is there any other better way to achieve this??

thanks for any help,

PKNT

Stuart Dootson29-Apr-09 20:48

29-Apr-09 20:48

Have you run it in a debugger (that's easy enough to do - just specify Matlab as the target executable) so you can see where the exception occurs?

Some things that do jump out at me:

As it says in the CreateThread[^] documentation,

A thread in an executable that calls the C run-time library (CRT) should use the _beginthreadex and _endthreadex functions for thread management rather than CreateThread and ExitThread; this requires the use of the multi-threaded version of the CRT. If a thread created using CreateThread calls the CRT, the CRT may terminate the process in low-memory conditions.
You pass a pointer to a stack variable in the CreateThread call. That's not a great idea - you can't guarantee that the newly created thread will assign to iter before i changes. Why not just pass the value of i rather than the address. Even though the param is an LPVOID, integer is convertible to LPVOID and vice versa.

One other thing - why use m_nThreads-1 all over the place - once your main thread enters WaitForMultipleObjects, there will be m_nThreads cores available for processing, as the WaitForMultipleObjects call will yield the core it's on.

Java, Basic, who cares - it's all a bunch of tree-hugging hippy cr*p

Kiran Satish30-Apr-09 5:15

30-Apr-09 5:15

Thanks for the reply... will try VC++ specific thread functions and see how it does and also the parameters thing.

Stuart Dootson wrote:
One other thing - why use m_nThreads-1 all over the place - once your main thread enters WaitForMultipleObjects, there will be m_nThreads cores available for processing, as the WaitForMultipleObjects call will yield the core it's on.

this is for the system to be responsive for other applications/tasks that are running at the same time. I am leaving a core for this purpose.

thanks

PKNT

Stuart Dootson30-Apr-09 6:16

30-Apr-09 6:16

Kiran Satish wrote:
this is for the system to be responsive for other applications/tasks that are running at the same time. I am leaving a core for this purpose.

That shows remarkable restraint Smile | :)

Java, Basic, who cares - it's all a bunch of tree-hugging hippy cr*p

Kiran Satish30-Apr-09 6:50

30-Apr-09 6:50

I figured out the problem... nothing from the way I am assigning threads (but now I am using _beginthread/_endthread functions though), but an overseen logic mistake and improper reading of 2D matrices from a 3D matrix generated using OptiVec library. Now everything works fine. Thanks for your time.

PKNT

Stuart Dootson30-Apr-09 6:55

30-Apr-09 6:55

Kiran Satish wrote:
nothing from the way I am assigning threads (but now I am using _beginthread/_endthread functions though), but an overseen logic mistake and improper reading of 2D matrices from a 3D matrix generated using OptiVec library

Doh!

Kiran Satish wrote:
Now everything works fine

Good

Kiran Satish wrote:
Thanks for your time

My pleasure

Java, Basic, who cares - it's all a bunch of tree-hugging hippy cr*p

KarstenK29-Apr-09 21:17

KarstenK

29-Apr-09 21:17

I was looking for a "i++" somewhere Dead | X|

Press F1 for help or google it.
Greetings from Germany

Kiran Satish30-Apr-09 3:27

30-Apr-09 3:27

Sorry, I do have i++ in there...

PKNT

KarstenK30-Apr-09 3:43

KarstenK

30-Apr-09 3:43

i didnt see it here: for (unsigned int i=0; i < m_nThreads-1; )

Press F1 for help or google it.
Greetings from Germany

Kiran Satish30-Apr-09 5:03

30-Apr-09 5:03

Well in the original program I have it, its a typo in y post and didn't had time to correct it in the morning when I replied to your reply.

PKNT

How can I make a combobox without using MFC

Joe Woodbury30-Apr-09 19:35

Joe Woodbury

30-Apr-09 19:35

for (unsigned int i=0; i < m_nThreads-1; i++ )
thd_handle[i] = CreateThread(NULL, GenerateThread, &i, 0, NULL);

The problem is that you are taking the address of i and passing it to the thread function. However, by the time the thread function is able to start, i has likely changed and is probably invalid.

Since all you need is the actual value, just pass i (by casting it to LPVOID), and then in the thread function just pass param to CreateResult by casting it to a DWORD.

(I also don't understand why you keep subtracting one from your thread count. Why not just use the correct number to begin with?)

Anyone who thinks he has a better idea of what's good for people than people do is a swine.
- P.J. O'Rourke

CodingLover29-Apr-09 16:24

CodingLover

29-Apr-09 16:24

Hi All,

I wonder how can I make a combobox without using MFC. Can someone give me a clue about that.

Thanks a lot

Re: How can I make a combobox without using MFC

Naveen29-Apr-09 17:56

Naveen

29-Apr-09 17:56

HWND hCombo = ::CreateWindow( _T("ComboBox"), _T("Some Name") , WS_VISIBLE|WS_CHILD|CBS_DROPDOWNLIST, 0,0, 300, 300, hParent, 0, hInstance,0 );

Where hParent is the parent window handle and hInstance is the instance handle of the application/module.

nave

[OpenedFileFinder] [My Blog]

CTreeCtrl - Get the number of the selected item

Gagnon Claude29-Apr-09 8:42

Gagnon Claude

29-Apr-09 8:42

Hi,

I have a CTreeCtrl in an application. When I click on an item, I want to do a particuliar action. To do that, I have to know the number of the item in the tree: first, second, third an so on.

How can I retreive that information ?

Thanks,

Claude

Re: CTreeCtrl - Get the number of the selected item

David Crow29-Apr-09 9:52

David Crow

29-Apr-09 9:52

Are tree controls supposed to be viewed that way. What happens to items 2..N when item 1 is expanded? Does item 2 become item 3, etc?

I would opt for using SetItemData() for each item/node in the tree.

Re: CTreeCtrl - Get the number of the selected item

Stuart Dootson29-Apr-09 10:51

Re: CTreeCtrl - Get the number of the selected item

29-Apr-09 10:51

Gagnon Claude wrote:
To do that, I have to know the number of the item in the tree: first, second, third an so on

Number in the tree....how are you counting? Breadth first? Depth first?

And why do you need that - are you sure there's no other way of achieveing your objective?

Java, Basic, who cares - it's all a bunch of tree-hugging hippy cr*p

led mike29-Apr-09 11:10

led mike

29-Apr-09 11:10

Stuart Dootson wrote:
how are you counting?

See there's this roulette wheel and Jig | [Dance]

Re: CTreeCtrl - Get the number of the selected item

Stuart Dootson29-Apr-09 11:48

Formatting A Rich edit control content in Editstream CallBack function

29-Apr-09 11:48

ForNow29-Apr-09 5:52

ForNow

29-Apr-09 5:52

Can I format the text to be displayed in a Rich Edit via Setsel ReplaceSel

in Editstream Call Back function before I copy it to the output buffer

thankx

Re: Formatting A Rich edit control content in Editstream CallBack function

David Crow29-Apr-09 6:37

David Crow

29-Apr-09 6:37

ForNow wrote:
Can I format the text to be displayed in a Rich Edit...before I copy it to the output buffer

Yes, maybe not with those exact methods, but you can edit/format it.

Re: Formatting A Rich edit control content in Editstream CallBack function

Stuart Dootson29-Apr-09 7:28