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Subj : Re: Windows Suspend/ResumeThread API equivalent for Linux or POSIX?
To   : comp.programming.threads
From : Chris Thomasson
Date : Wed May 11 2005 07:12 pm

>> In order to call the Windows GetThreadContext Thread API, you need to use 
>> the Resume/SuspendThread API. I am reading thread context and comparing 
>> against deferred pointers in a modified SMR polling algorithm; You can 
>> eliminate the hazard pointer reload and compare by doing this.
>
>    Sounds like doing an awful lot of work to save a small amount of work.

:)




> Suspending a thread without its cooperation is an incredibly expensive 
> thing to do.

Yes. Luckily, the algorithm assumes that. The polling algorithm in question 
only runs about every five seconds, or when the total number of deferred 
objects hits a certain level, its usually set to about a half-million nodes. 
This is sufficient for many "read-mostly" data structures. Using thread 
context for an algorithm that had a moderate and somewhat persistent number 
of writes would be way too expensive. Anyway, I am not really advocating 
scanning thread context to implement SMR. I want to gather a number of 
different somewhat portable methods together so I can show how my new 
algorithm differs from each one.




>> I was wondering if Linux and/or POSIX has a way to get thread context and 
>> if it was similar to the way windows does it. Something like:
>>
>> pthread_suspend_np( pthread_t, ucontext_t* );
>> pthread_resume_np( pthread_t );
>
>    No.

Ok. How about any Linux specific function to grab a copy of a thread's 
context? I am not a Linux Kernel guru.




> What could you do while the thread was suspended?

> How can you be sure you don't trip over a lock the suspended thread holds?

Yes, this can be so dangerous...

Microsoft recommends that the thread that calls SuspendThread API not hold 
and/or access "any" sync objects:

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dllproc/base/suspendthread.asp

If you can't guarantee this with 100% certainty, then using SuspendThread is 
like playing with a lit stick of dynamite.

:)

.

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