StackThreads and Phobos

[Bruno Medeiros]

mclysenk at mtu.edu wrote:
> In article <e8artd$16e0$1 at digitaldaemon.com>, Bruno Medeiros says...
>> Unless my understanding of this is wrong, the use of the word "never" 
>> (gets collected) is too strong. If during normal program flow the stack 
>> is overwritten again, the reference becomes free. Or am I missing something?
>> Also, doesn't this happen with any regular function?
>>
> 
> Well, you are correct, that it may still get collected in the future -
> regardless, its prospects are fairly dim.  You are also right in your statement
> that this is not abnormal behavior for functions, and the GC knows this.  It has
> a special case which handles the stack of a regular function.
> 
> When the GC does a full collect, it pauses all threads and marks the range from
> the stack pointer to the bottom of the stack.  This prevents it from scanning
> stuff which is no longer valid, since that range never gets marked.  This works
> very well.
> 
> The bad part happens when we create multiple stacks for one thread.  In order
> for the GC to properly scan them, we need to mark their stack when it is not in
> use.  If the GC didn't scan their stack, then we'd accidentally over-collect
> stuff they were using.  If we mark the entire stack range, then we'd
> under-collect and get a bunch of memory leaks.  To fix this, we use addRange to
> mark the active part of their stack before we switch out their context, and
> removeRange to delete their old - and potentially invalid - stack range when we
> switch into their context.
> 
> This part is tricky, and it burned me many times while I was working on stack
> threads before I finally caught on.  It is not a big deal to fix once you know
> what's happening.  The main disadvantage at the moment is removeRange - it's
> just too slow!  It can be fixed, but it requires changing phobos.  
> 
> -Mikola Lysenko
> 
> 

That was clear now, but for what I understand, then your problem is 
simply that you must use removeRange(and it is slow).
That is, it doesn't really have to do with function contexts and stacks. 
Anyone who allocates manually managed memory for any purpose, and then 
uses addRange on it, will have the same problem, right? (because they 
too will have to use removeRange)

-- 
Bruno Medeiros - CS/E student
http://www.prowiki.org/wiki4d/wiki.cgi?BrunoMedeiros#D