How to stop the thread if it's running?

mikert_2008

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

CPallini

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]

mikert_2008

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

Cedric Moonen

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++

CPallini

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

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]

Rajesh R Subramanian

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

Rajesh R Subramanian

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 WaitFor_Whatever_ 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

Cedric Moonen

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++

Rajesh R Subramanian

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? :) 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

Roger Stoltz · modified on Thursday, April 30, 2009 4:50 AM

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! :-\ Need more caffeine in the morning so I can read and distinguish between the letters in TRUE and FALSE. :java::java::java::java:

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

Rajesh R Subramanian

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

Roger Stoltz · modified on Thursday, April 30, 2009 4:48 AM

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... :-O

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

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

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?

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]

Rajesh R Subramanian

The issues with what you've done are: 1. You haven't shown us what you're doing inside the 'run' function. (can you please rename it to something other than run, I'm just terrified looking at the context - CWinThread::Run() ... you get the picture) 2. Your WaitFor... call does not 'wait', it just performs a check on a thread which might be running or might be dead, and then attempts to delete something which (again) may have been already dead (you haven't set the m_bAutoDelete to TRUE). You may first try to run a thread successfully, and then try using Events with WaitFor... functions. Simulate processing with Sleep(10) within a loop (for learning purposes) and then shut it down gracefully by setting an Event. You need not 'delete' the CWinThread object, like I said. Give that excellent article another read, and you will be all set. Post a reply, if you're stuck somewhere.

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

Rajesh R Subramanian

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

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

Rajesh R Subramanian

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

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

Roger Stoltz

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

Rajesh R Subramanian

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. :)

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

Roger Stoltz

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. :-D

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

Rajesh R Subramanian

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. :-D

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