.NET (Core and Framework)

Safe thread termination in unmanaged code

9-Apr-09 10:56

mohamedmrc wrote:
thinks

Indeed, give that a try.

Re: hello

Pete O'Hanlon12-Apr-09 11:03

Pete O'Hanlon

12-Apr-09 11:03

led mike wrote:
mohamedmrc wrote:
thinks

Indeed, give that a try.

It'll never catch on.

"WPF has many lovers. It's a veritable porn star!" - Josh Smith

As Braveheart once said, "You can take our freedom but you'll never take our Hobnobs!" - Martin Hughes.

My blog | My articles | MoXAML PowerToys | Onyx

supercat99-Apr-09 8:06

supercat9

9-Apr-09 8:06

If I have a quantity of unmanaged code (in C, designed for another system), and most of it could be safely terminated at any time but it makes callbacks into managed code which could not be so terminated, would it be safe to do something like:

/* In the unmanaged section */
volatile int statflag;
/* Zero when running C code that may be terminated.
   One when running code that must not be terminated.
   Two when termination has been requested */

  if (Exchange(&statflag, 1) == 0)
  {
    call_managed_code();
    if (Exchange(&statflag, 0) != 1))
      terminate();
  }
  else
    terminate();

' In the other thread...
  If Threading.Interlocked.Exchange(safeflag, 2) = 0 Then
    TheThread.Terminate

If the portion of the code which is in C never does anything that could not be safely stopped asynchronously while safeflag is one, would there be any danger in calling Terminate() upon such a thread? Obviously any resources that had been allocated by that thread would have to be freed elsewhere, but in this particular application I'm not expecting the unmanaged code to use only resources that are given to it by other code (which could then take care of any necessary de-allocation).

In the particular application, there is a risk that the C portion of the code could hang without any callbacks to the managed portion, so I'd like to be able to use something more "potent" than Thread.Interrupt; is Thread.Terminate safe if used only upon a thread which is known not to hold any locks or be manipulating any other dangerous constructs?

led mike9-Apr-09 9:10

9-Apr-09 9:10

supercat9 wrote:
would there be any danger in calling Terminate() upon such a thread?

Hi again, welcome to CodeProject. Let me just warn you that many of the regular members here will tend to flame on people who are obviously not reading the documentation.

TerminateThread[^]

TerminateThread is a dangerous function that should only be used in the most extreme cases.

Terminating threads is never considered Best Practice. On the other hand if you have no other choice then it really doesn't matter what dangers might exist. Obviously, if you do have another choice then go with the other choice.

supercat99-Apr-09 9:44

supercat9

9-Apr-09 9:44

Hi again, welcome to CodeProject. Let me just warn you that many of the regular members here will tend to flame on people who are obviously not reading the documentation.

It states that it is a dangerous function that should only be used in extreme cases. I can certainly appreciate that many bad things can happen if it is done on managed code or code which uses the Windows API. My situation is a bit different from the usual one, though, and I was wondering whether anyone had done anything similar.

I'm writing code for a microcontroller with a few kbytes of RAM and a few dozen kbytes of code. For testing purposes, I would like to be able to run the code on a Windows machine, replacing the physical I/O routines with calls to wrapper functions which would call back into managed code that would simulate the I/O in question. If every call to a wrapper function checks for a "terminate, please" flag, then any loop which calls any of the wrapper functions will exit once the flag in question is set, but there's no guarantee of when that will actually take place. If something goes wrong in the target system code, such callbacks might never take place.

Since the target application shouldn't get stuck in such a loop, it probably wouldn't be the end of the world to require that someone use ctrl-alt-del and kill the non-responsive application, but that would seem more dangerous than having the application terminate the stuck thread, especially since the application might be doing things on other threads that should not be blindly terminated.

led mike9-Apr-09 10:55

9-Apr-09 10:55

supercat9 wrote:
For testing purposes

For testing I would think as long as you can accomplish the testing goals you wouldn't care about the dangers. I imagine the author talking about dangers is addressing production software environments.

supercat99-Apr-09 11:43

supercat9

9-Apr-09 11:43

I imagine the author talking about dangers is addressing production software environments.

The system might get used in something between a testing and production environment; the actual hardware device includes the ability to initiate TCP connections to a server, and it's possible that customers might use the "simulator" to simulate having a number of devices connecting to the server at once. By the time the code gets to the customer it shouldn't get into bad situations, but in case something bad happens (e.g. the server comes back with a response that would confuse the device) it would be nicer to allow a controlled shutdown of the thread than to force the user to kill the application.

I guess my main question should perhaps have been better phrased as, "The documentation says to avoid using TerminateThread; is there any accepted style for wrapping it in those circumstances where its use may be reasonably safe and appropriate?" I guess if there's no way to recover the stack in older versions of Windows that would be bad, but it could still be better than having a stuck thread gobble up all the CPU time it can get.

On a related note, under what circumstances is an "isBackground" thread killed off blindly when an application terminates? If a thread is doing a "WriteAllText" to create and write a file, is the function guaranteed to either fail altogether or succeed completely in case of application termination, or should it be surrounded by saving the isBackground property of the current thread, setting it to False, performing the function, and restoring the old value of isBackground?

In any case, thanks for responding. -- John

Luc 64801110-Apr-09 2:57

Luc 648011

10-Apr-09 2:57

supercat9 wrote:
under what circumstances is an "isBackground" thread killed off blindly

AFAIK it always is. Therefore it is a bad idea to use a background thread for writing files and databases.

Smile | :)

led mike10-Apr-09 5:37

am i a programmer or not [modified]

10-Apr-09 5:37

supercat9 wrote:
"The documentation says to avoid using TerminateThread;

Well I thought I already covered this but let's have another go.

led mike wrote:
Terminating threads is never considered Best Practice. On the other hand if you have no other choice then it really doesn't matter what dangers might exist. Obviously, if you do have another choice then go with the other choice.

What it comes down to is if you can accomplish what is needed without terminating threads (stop the thread gracefully), do it that way, always, period. However if for some reason terminating threads is all you can do and you must do it, then it doesn't matter if there are dangers does it?

Now to me that seems like a pretty simple concept. However you seem to be thinking along another line that I have so far failed to understand.

rilm9-Apr-09 7:48

rilm

9-Apr-09 7:48

hi, i have a question about my way of programming
if i want to make a program i start with a skeleton and start with
nothing, if i dont know something lets say winsock i go look for sample programs, i start look what each line of code does and what its for and
start recoding to use it in my program.further a long the way i find it easier to go on.
when something isn't working, even if it take me a month i go on til it does work.although i don't know why(because i don't really know how it al works)it doesn't work, i kind of know it but its just like its a littly foggy.
for example i was once working on a program and there was a error somewhere in my code,the whole time i knew wich lines maybe causing the problem
but it took me a month befor i tried it.
and when i want to make a program i will get it done so my question is
am i a programmer or should i stop with its more like a hobby because my education is to low and i want it so bad to be a freelance programmer.
i tried several languages vc++ html css php mysql and now in win32 assembly.
thanks in advance

3 things
1 maybe i am contradicting myself: so what, don't apply to my message i, don't need answer from
arrogant people who think they know how someone is, by reading their letter.
2 i had to learn all of it in english so that makes it a little harder, it's not my language.
i don't had a high adducation what you need for programming so i learned it all by myself
so doesn't that say something for me ?
3 please only answer if you can leave me in my value

for all those people who can please reply
sorry for my poor english but i am sure that it is understandable

thanks for the reactions, and im not giving it up here is where my hart lies and i keep learning.

i know what a pointer is etc. but my problems are that there isn't a good book in my language
and the absence of someone to ask things, most books say how a function works what regs and/or flags
it affects but i can't ask what can we do with the changed flags this is just an example,what i mean is the questions i have i can't ask in programmer groups, the answer i offen get is i have to read more books but the books don't have the answers to the questions i have.

modified on Wednesday, April 15, 2009 1:24 PM

Paulo Zemek9-Apr-09 8:19

Paulo Zemek

9-Apr-09 8:19

Your are a hobbist. This does not mean you are not able to become a better programmer, but for the question itself, you are unsure.
My question is: Do you like programming? Are you thinking about giving up this area?

led mike9-Apr-09 8:41

9-Apr-09 8:41

Paulo Zemek wrote:
Your are a hobbist.

If you meant "you're" as in "you are" a hobbist, really? So he is one of these?

hobbist
One entry found.

Main Entry:
    Hob·bism Listen to the pronunciation of Hobbism
Pronunciation:
    \ˈhä-ˌbi-zəm\ 
Function:
    noun 
Date:
    1691

: the philosophical system of Thomas Hobbes ; especially : the Hobbesian theory that 
people have a fundamental right to self-preservation and to pursue selfish aims but 
will relinquish these rights to an absolute monarch in the interest of common safety 
and happiness

dojohansen15-Apr-09 1:40

dojohansen

15-Apr-09 1:40

That reply was as unhelpful and arrogant and generally evil-spirited as this one is from me. Only my target is you, and unlike you he did *nothing* to invite such treatment.

led mike15-Apr-09 11:49

15-Apr-09 11:49

dojohansen wrote:
he did *nothing* to invite such treatment.

Nothing? Really? What about where he posted "your" for "you are" and "hobbist" for "hobbyist", which is all I pointed out, and yet somehow you think this qualifies as "evil-spirited". What a retard. Roll eyes | :rolleyes:

Frakoff icehole.

dojohansen16-Apr-09 0:44

dojohansen

16-Apr-09 0:44

Yeah, people who make accidental spelling mistakes are really asking for it. Lay it on them.

I wouldn't have bothered commenting if it weren't for the fact that I noticed it was you and I had been reading forum posts for a while and your name kept popping up next to unhelpful and condescending posts over and over again. At first I thought I'd just stay above that, but after a while I thought "damn, I think this is the tenth mean posting by this dude and I've yet to see him contribute anything constructive. To hell with normal standards of conduct - he's not worthy".

Obviously you're unlikely to even stop a second and ask yourself if there may be a grain of truth in my criticism, but just maybe someone else will think "you know what, he's right - I'm going to watch myself so I don't start behaving like this led mike dude". And if so, the world will be a (slightly) better place.

Feel free to further demonstrate your intellectual powers/emotional maturity by emitting more of the frakoff icehole stuff, it'll be the highlight of my day.

led mike16-Apr-09 5:18

16-Apr-09 5:18

dojohansen wrote:
Lay it on them.

Yeah, I really laid into that guy by posting the definition of the word he mistakenly posted. Have you lived an exceptionally sheltered life?

dojohansen wrote:
I've yet to see him contribute anything constructive.

Well by all means, you must the authority on everything I have done then. Game over.

dojohansen wrote:
Obviously you're unlikely to even stop a second and ask yourself if there may be a grain of truth in my criticism

I don't need to, I know it's true.

dojohansen wrote:
I'm going to watch myself so I don't start behaving like this led mike dude"

Please, give it a try, you might find that I just make it look easy.

dojohansen wrote:
Feel free to further demonstrate your intellectual powers/emotional maturity by emitting more of the frakoff icehole stuff, it'll be the highlight of my day.

I will probably regret this but text is cheap. First I don't owe you or anyone else any explanation, however on the off chance you are posting all your drivel because you are actually interested, here goes.

You might notice that I have helped many people on this site for the entire time I have been here if you bother to look at my profile and match up my start date with my MVP awards. When I first started encountering these idiots that come to this site I was like everyone else and attempted to offer polite assistance. After a while it was obvious that polite assistance was not getting through to them. Then while laughing at one of these morons post one day I typed in my humorous thoughts. The response to the post was overwhelming. I decided to try more of this. In a short time it was obvious that, at the very least, these monkeys actually read these types of posts rather than just ignoring them. In some rare cases it has even helped them to see there failed perspective on the work they are doing.

Anyway, since there was small successes and they are sometimes humorous, I generally go that way. However I do mix in an occasional normal reply just to make sure I don't forget how.

Ok, that's the short version. Since you likely just decided to have a go at me I don't imagine this will change that so, you're up, flame away.

dojohansen16-Apr-09 5:29

dojohansen

16-Apr-09 5:29

led mike wrote:
Ok, that's the short version. Since you likely just decided to have a go at me I don't imagine this will change that so, you're up, flame away.

Thanks for that, and no thanks, I've no desire to flame.

I'm not sure I share your belief in the efficacy of your "technique", but I'd like to believe that you really have a constructive intent, however well hidden it may be (to me at least). So I'll just take your word for it. I do think that attacking people specifically for spelling or grammar errors is a bit unfair though. I may be mistaken, but I'm under the impression that codeproject isn't a US-specific community, and while I obviously realize it's in my own best interest to post in English rather than my native Norwegian or my current host culture's French I think those who make an effort to use your language do not deserve ridicule and harassment for nothing more than using it imperfectly.

Those who post to ask others basically to just do the work for them may deserve a bit of a kick though, so maybe you can reserve this particular talent of yours for them. Just a suggestion. Smile | :)

led mike16-Apr-09 7:30

16-Apr-09 7:30

dojohansen wrote:
I'm not sure I share your belief in the efficacy of your "technique"

It seems you do share it since it's doubtful. Wink | ;)

dojohansen wrote:
but I'd like to believe that you really have a constructive intent

It is the primary reason I spend any time on this site. I ~~may~~ do digress time to time.

dojohansen wrote:
I do think that attacking people specifically for spelling or grammar errors is a bit unfair though. I may be mistaken

Nah, you're not mistaken, I just didn't really consider it an attack, more like a jab or dig. And I specifically didn't recognize that poster as non english. I do agree with you and normally don't comment on typo or language issues other than leet or text speak.

dojohansen wrote:
Those who post to ask others basically to just do the work for them may deserve a bit of a kick though, so maybe you can reserve this particular talent of yours for them. Just a suggestion.

Thank you, that's a good suggestion. Also your sincerity surprises me, it seems my reply was worth the effort. Feel free to reign me in anytime. Big Grin | :-D

led mike9-Apr-09 8:43

9-Apr-09 8:43

rilm wrote:
i start with a skeleton and start with
nothing

Apparently you start with a contradiction. Laugh | :laugh:

That's enough for me, I'm not reading any more of it. Good luck.