Suspending threads

Suspending threads

Hi,

If I create a thread in the non-suspended state and then call:

SuspendThread(hThread);

how do I know that the thread isn't already suspended when I call this?
Ideally, I'd like something like this:

if (GetThreadSuspendCount(hThread) == 0)
    SuspendThread(hThread);

but the MSDN documentation is a little unhelpful here.

Thanks,
Alain

date: Thu, 14 Aug 2008 14:31:32 +0100 author: Alain Dekker

Re: Suspending threads

On Thu, 14 Aug 2008 14:31:32 +0100, "Alain Dekker"
 wrote:

>Hi,
>
>If I create a thread in the non-suspended state and then call:
>
>SuspendThread(hThread);
>
>how do I know that the thread isn't already suspended when I call this?
>Ideally, I'd like something like this:
>
>if (GetThreadSuspendCount(hThread) == 0)
>    SuspendThread(hThread);
>
>but the MSDN documentation is a little unhelpful here.
>
>Thanks,
>Alain 
>

If the function succeeds, the return value is the thread's previous suspend
count; otherwise, it is 0xFFFFFFFF. To get extended error information, use
the GetLastError function. 


if (SuspendThread(hThread) > 0)
    ResumeThread(hThread);

date: Thu, 14 Aug 2008 08:33:16 -0700 author: Geoff lid

Re: Suspending threads

"Alain Dekker"  wrote in message 
news:OQYF0Gh$IHA.4648@TK2MSFTNGP04.phx.gbl...
> Hi,
>
> If I create a thread in the non-suspended state and then call:
>
> SuspendThread(hThread);
>
> how do I know that the thread isn't already suspended when I call this?
> Ideally, I'd like something like this:
>
> if (GetThreadSuspendCount(hThread) == 0)
>    SuspendThread(hThread);
>
> but the MSDN documentation is a little unhelpful here.


Actually the MSDN docs describe it completely.

Beware of using SuspendThread() unless you're writing a debugger.
You have NO control over where (in the execution) the thread gets 
suspended...this can cause problems like deadlocks and data corruption.

Mark

-- 
Mark Salsbery
Microsoft MVP - Visual C++


>
> Thanks,
> Alain
>

date: Thu, 14 Aug 2008 09:34:34 -0700 author: Mark Salsbery [MVP] MarkSalsbery[MVP]@newsgroup.nospam

Re: Suspending threads

Hi Mark,

If the MSDN documentation describes it completely, therefore the answer 
(which is not described, but surely I should have inferred this) is that I 
cannot get the SuspendCount of the thread before I call SuspendThread(...)! 
Thats a pity.

Thanks for the answer. What I'll do is to track the return from 
SuspendThread to ensure it doesn't get called twice.

Is there any way to suspend a thread in a known state, by for example, 
getting it to restart at a certain point in the execution? I have an 
application that uses threads to communicate with COM ports, read processor 
load using WMI, communicate across the network for reporting and so on. If 
one or more of those threads is not required, I'd like to suspend it to save 
processing power since its a pretty high-speed app and the main thread needs 
all the processor time it can get (without completely starving the other 
threads!).

Got any suggestions or things I should considerations for this type of 
"Suspend-Resume-Suspend-Resume" chain?

Thanks and regards,
Alain


"Mark Salsbery [MVP]" <MarkSalsbery[MVP]@newsgroup.nospam> wrote in message 
news:u4C3pui$IHA.4616@TK2MSFTNGP06.phx.gbl...
> "Alain Dekker"  wrote in message 
> news:OQYF0Gh$IHA.4648@TK2MSFTNGP04.phx.gbl...
>> Hi,
>>
>> If I create a thread in the non-suspended state and then call:
>>
>> SuspendThread(hThread);
>>
>> how do I know that the thread isn't already suspended when I call this?
>> Ideally, I'd like something like this:
>>
>> if (GetThreadSuspendCount(hThread) == 0)
>>    SuspendThread(hThread);
>>
>> but the MSDN documentation is a little unhelpful here.
>
>
> Actually the MSDN docs describe it completely.
>
> Beware of using SuspendThread() unless you're writing a debugger.
> You have NO control over where (in the execution) the thread gets 
> suspended...this can cause problems like deadlocks and data corruption.
>
> Mark
>
> -- 
> Mark Salsbery
> Microsoft MVP - Visual C++
>
>
>>
>> Thanks,
>> Alain
>>

date: Fri, 15 Aug 2008 07:20:29 +0100 author: Alain Dekker

Re: Suspending threads

"Alain Dekker"  wrote in message 
news:uSyUp7p$IHA.3964@TK2MSFTNGP06.phx.gbl...
> Hi Mark,
>
> If the MSDN documentation describes it completely, therefore the answer 
> (which is not described, but surely I should have inferred this) is that I 
> cannot get the SuspendCount of the thread before I call 
> SuspendThread(...)! Thats a pity.
>
> Thanks for the answer. What I'll do is to track the return from 
> SuspendThread to ensure it doesn't get called twice.
>
> Is there any way to suspend a thread in a known state, by for example, 
> getting it to restart at a certain point in the execution? I have an 
> application that uses threads to communicate with COM ports, read 
> processor load using WMI, communicate across the network for reporting and 
> so on. If one or more of those threads is not required, I'd like to 
> suspend it to save processing power since its a pretty high-speed app and 
> the main thread needs all the processor time it can get (without 
> completely starving the other threads!).
>
> Got any suggestions or things I should considerations for this type of 
> "Suspend-Resume-Suspend-Resume" chain?


I typically use event synchronization objects.

Here's an example (pseudocode) using two events to wake a thread - one to 
tell the thread to terminate and one to signal the thread to do some work. 
The events can be signaled by any other thread...

threadproc
{
   while (1)
   {
      // block until an event is signaled
      waitformultipleobjects(terminateevent, dosomeworkevent);

      if (terminateevent was signaled)  break;

       ... do some work then loop and wait for next event ...
   }
}


Mark

-- 
Mark Salsbery
Microsoft MVP - Visual C++



>
> Thanks and regards,
> Alain

date: Fri, 15 Aug 2008 11:37:50 -0700 author: Mark Salsbery [MVP] MarkSalsbery[MVP]@newsgroup.nospam