Re: How to stop the thread if it's running? - C / C++ / MFC Discussion Boards

detonation99729-Apr-09 21:22

29-Apr-09 21:22

Recently I found a code-snippet in C++ on wikipedia. It's used to work with CUDA:
http://en.wikipedia.org/wiki/CUDA[^]

In the last line of

dim3 blockDim(16, 16, 1);
dim3 gridDim(width / blockDim.x, height / blockDim.y, 1);
kernel<<< gridDim, blockDim, 0 >>>(d_odata, width, height);

they are using these operators (or whatever) with "kernel" being a function:

__global__ void kernel(float* odata, int height, int width)
{
   unsigned int x = blockIdx.x*blockDim.x + threadIdx.x;
   unsigned int y = blockIdx.y*blockDim.y + threadIdx.y;
   float c = texfetch(tex, x, y);
   odata[y*width+x] = c;
}

What's the purpose for <<< and >>>? Thx for your answer!

Re: What does <<< or >>> mean?

C^hris L^osinger30-Apr-09 2:43

C^hris L^osinger

30-Apr-09 2:43

from the CUDA dev guide[^]:

kernel <<< X, Y >>> (...)

defines a grid of X x Y threads which will execute in parallel

image processing toolkits | batch image processing

How to stop the thread if it's running?

mikert_200829-Apr-09 21:01

mikert_2008

29-Apr-09 21:01

Hi,
I have created the thread using AfxBeginThread(); function. Now my problem is

1. How to check wheather Thread is running?
2. If it is running then stop/kill the thread.

This I will put in the destructor of class (which starts the thread) to do error handling.

How to do this?

Mike

Re: How to stop the thread if it's running?

CPallini29-Apr-09 21:06

CPallini

29-Apr-09 21:06

See [^].

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]

Re: How to stop the thread if it's running?

mikert_200829-Apr-09 21:19

mikert_2008

29-Apr-09 21:19

Thanks for the link given.

So now I used it like following.

CWinThread * myWorkerThread;
myWorkerThread = AfxBeginThread(run, this);

In ~Destructor()
{
DWORD result =WaitForSingleObject(myWorkerThread->m_hThread,0);

if(result == WAIT_OBJECT_0)
delete myWorkerThread;
}

Is this is the correct apporch to do this?

Mike

Re: How to stop the thread if it's running?

Cedric Moonen29-Apr-09 21:29

Cedric Moonen

29-Apr-09 21:29

No, because you don't stop the thread. So, how can it stop ?
Usually, to stop a thread you set a flag to false and this flag is constantly checked within your thread function. Once it is false, the function exits, which stops the thread.
But I guess everything is described in the article Carlo gave to you.

Cédric Moonen
Software developer

Charting control [v2.0]
OpenGL game tutorial in C++

Re: How to stop the thread if it's running?

Rajesh R Subramanian29-Apr-09 22:05

Rajesh R Subramanian

29-Apr-09 22:05

Cedric Moonen wrote:
Usually, to stop a thread you set a flag to false and this flag is constantly checked within your thread function. Once it is false, the function exits, which stops the thread.

I'll be surprised if you are doing such a thing. What about the usage of Events with WaitForWhatever functions? Polling for a boolean is not the best approach, IMO, and definitely shouldn't be suggested to a rookie programmer. Not to mention that you will need to then explain the OP what optimization is and why does the optimizer have to be prevented from optimizing this particular boolean variable, and then there comes volatileness, and ...

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

Re: How to stop the thread if it's running?

Cedric Moonen29-Apr-09 22:11

Cedric Moonen

29-Apr-09 22:11

Yes, sure. But even if you are using events to signal your thread that "data is available for processing", you still need a way to tell the thread that it should stop. Otherwise, having a thread that just wait on an event and stops when the event is signaled is a bit pointless.

But as I said in my message, it was a rough advice as everything is clearly explained in the article. My point was that you need a way to tell the thread that it's job is done, and usually you do this using a flag.

Cédric Moonen
Software developer

Charting control [v2.0]
OpenGL game tutorial in C++

Re: How to stop the thread if it's running?

Rajesh R Subramanian29-Apr-09 22:19

Rajesh R Subramanian

29-Apr-09 22:19

At times, it gets ugly with a boolean and I use two events, and two WaitFor... functions one after another. The first one checks if the thread should shut down, and the second one checks if there's data for processing and proceeds if there is. Based on the requirements, the events may be manual or auto reset. Threads are a fascinating thing, aren't they? Smile | :)

My reply was based on an assumption that you used a boolean for both. I was not kinda terrified.

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

Re: How to stop the thread if it's running?

CPallini29-Apr-09 21:40

CPallini

29-Apr-09 21:40

As a side note to Cédric reply, ponder the usage of the m_bAutoDelete flag. Bottom line: read carefully the article I linked.
Smile | :)

Re: How to stop the thread if it's running? [modified]

Rajesh R Subramanian29-Apr-09 22:00

Rajesh R Subramanian

29-Apr-09 22:00

You need not (and in most cases, MUST NOT) be deleteing a CWinThread object. It cleans up its own mess, unless you change the default value of m_bAutoDelete variable before the thread starts. And if you're thinking of changing the value of m_bAutoDelete , I can almost confidently tell that your approach is wrong (it is so, in 90% of the cases). If you knew what m_bAutoDelete is, you won't be asking here on how to shut down a thread gracefully.

Fixed typo!

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

modified on Thursday, April 30, 2009 4:50 AM

Re: How to stop the thread if it's running?

Roger Stoltz29-Apr-09 22:26

Roger Stoltz

29-Apr-09 22:26

Rajesh R Subramanian wrote:
And if you're thinking of setting m_bAutoDelete to TRUE, I can almost confidently tell that your approach is wrong (it is so, in 90% of the cases).

Quite the contrary Rajesh.
In order to wait for the thread the thread handle must be valid and since the CWinThread destructor closes the handle. This issue is also addressed in the article.

Forget it! $Shucks | :-\$
Need more caffeine in the morning so I can read and distinguish between the letters in TRUE and FALSE.
Java | [Coffee]

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

Re: How to stop the thread if it's running?

Rajesh R Subramanian29-Apr-09 22:30

Rajesh R Subramanian

29-Apr-09 22:30

Well, I am not contradicting the article, but most code that I've reviewed through, especially written by inexperienced programmers, which were reported 'not working' and had memory leaks, had the default value of m_bAutoDelete was manually changed for absolutely no sane reasons. Therefore my comment. I remember having posted one of such horrible codes in the coding horror board (or at thedailywtf), if I'm right.

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

modified on Thursday, April 30, 2009 4:48 AM

Re: How to stop the thread if it's running?

Roger Stoltz29-Apr-09 22:35

Roger Stoltz

29-Apr-09 22:35

I know, I know, I know.....
I've modified my previous post even before you replied.
You were right in first place Rajesh. I jumped to conclusions from your discussion with Cédric.
I'll just put a sock in it now... Blush | :O

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

Re: How to stop the thread if it's running?

Rajesh R Subramanian29-Apr-09 22:51

Rajesh R Subramanian

29-Apr-09 22:51

Nah, it looks like I need some coffee as well. Modified my post such that it makes clear sense. Big Grin | :-D

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

Re: How to stop the thread if it's running?

CPallini29-Apr-09 22:42

CPallini

29-Apr-09 22:42

Rajesh R Subramanian wrote:
It cleans up its own mess, unless you set the m_bAutoDelete variable to TRUE before the thread starts.

Is quite the opposite, I suppose. Am I wrong?

Re: How to stop the thread if it's running?

Rajesh R Subramanian29-Apr-09 22:49

Rajesh R Subramanian

29-Apr-09 22:49

You are FRAKKIN' RIGHT! It was a typo, but now fixed it to something that cannot go wrong. Smile | :)

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

Re: How to stop the thread if it's running?

Roger Stoltz29-Apr-09 22:52

Roger Stoltz

29-Apr-09 22:52

CPallini wrote:
Rajesh R Subramanian wrote:

It cleans up its own mess, unless you set the m_bAutoDelete variable to TRUE before the thread starts.

Is quite the opposite, I suppose. Am I wrong?

Just to be clear:
If CWinThread::m_bAutoDelete is set to TRUE, the destructor closes the thread handle. To be able to wait on the thread handle from another thread m_bAutoDelete must be set to FALSE.

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

Re: How to stop the thread if it's running?

Rajesh R Subramanian29-Apr-09 22:56

Rajesh R Subramanian

29-Apr-09 22:56

I think Carlo was talking with regards to be able to manually 'delete' the CWinThread object, which can be done with the m_bAutoDelete member set to FALSE. Smile | :)

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

Re: How to stop the thread if it's running?

Roger Stoltz29-Apr-09 23:04

Roger Stoltz

29-Apr-09 23:04

Rajesh R Subramanian wrote:
I think Carlo was talking with regards to be able to manually 'delete' the CWinThread object

I understood it differently.
I think he's talking about that your sentence can be interpreted as "if m_bAutoDelete is set to TRUE, CWinThread will not clean up its own mess".
You've got a way with words Rajesh. Big Grin | :-D

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

Re: How to stop the thread if it's running?

Rajesh R Subramanian29-Apr-09 23:11

Rajesh R Subramanian

29-Apr-09 23:11

Roger Stoltz wrote:
I think he's talking about that your sentence can be interpreted as "if m_bAutoDelete is set to TRUE, CWinThread will not clean up its own mess".

It occurred to me as well, but I went through the whole conversation again and finally found out something that made sense. Now, let's hope Carlo doesn't come up to tell us he was actually talking about Pasta and Rosemary. Big Grin | :-D

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

Re: How to stop the thread if it's running?

CPallini29-Apr-09 23:34

CPallini

29-Apr-09 23:34

Rajesh R Subramanian wrote:
Carlo doesn't come up to tell us he was actually talking about Pasta and Rosemary.

Nope, you should know, I was actually talking about pizza 'napoli' and beer.
Big Grin | :-D

Re: How to stop the thread if it's running?

CPallini29-Apr-09 23:32

CPallini

29-Apr-09 23:32

If I recall well, that isn't the whole story, The CWinThread pointer is deleted too.
Smile | :)

Re: How to stop the thread if it's running?

Roger Stoltz29-Apr-09 23:40

Roger Stoltz

29-Apr-09 23:40

CPallini wrote:
If I recall well, that isn't the whole story, The CWinThread pointer is deleted too.

You recall correctly! Thumbs Up | :thumbsup:

There's a delete this; in the destructor as well that is executed if m_bAutoDelete is set to TRUE.
I omitted it for brevity since I considered the name of the variable m_bAutoDelete rather self-explanatory. Wink | ;)

But the only thing the OP need is to read Joe's article over and over again until it's understood. Really.

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

Re: How to stop the thread if it's running?

CPallini29-Apr-09 23:44

CPallini

29-Apr-09 23:44

Roger Stoltz wrote:
But the only thing the OP need is to read Joe's article over and over again until it's understood. Really.

"Softly spoken magic spells".
Smile | :)

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