MutVar# and GC

[chessai .]

Cheng,

That's perfect. Thanks

On Thu, Jan 17, 2019, 11:51 PM Shao, Cheng <cheng.shao at tweag.io wrote:

> Hi,
>
> I believe it's mentioned here:
>
>
> https://ghc.haskell.org/trac/ghc/wiki/Commentary/Rts/Storage/GC/RememberedSets
>
> Regards,
> Shao Cheng
>
> On Fri, Jan 18, 2019, 12:34 PM chessai . <chessai1996 at gmail.com> wrote:
>
>> Ryan,
>>
>> That makes perfect sense, thanks. Is that documented explicitly anywhere?
>> If not, I'd like to add the documentation to any place relevant.
>>
>> Thanks
>>
>> On Thu, Jan 17, 2019, 8:19 PM Ryan Yates <fryguybob at gmail.com wrote:
>>
>>> Hi,
>>>
>>> Because GHC's GC is generational it needs a way to handle heap objects
>>> from older generations that point into younger generations.  This only
>>> happens when an older object is mutated to point to a younger object.  GHC
>>> solves this by invoking the GC write barrier (not to be confused with write
>>> barriers for memory synchronization) `dirty_MUT_VAR`.  This will add that
>>> mutable object to a mutable list that will be traversed in minor GCs along
>>> with young generation roots.  Additionally the write barrier will mark the
>>> heap object as "dirty" to avoid adding it to the list more than once.
>>>
>>> Ryan
>>>
>>> On Thu, Jan 17, 2019 at 4:29 PM chessai . <chessai1996 at gmail.com> wrote:
>>>
>>>> Devs,
>>>>
>>>> I've heard from a few friends that MutVars, TVars, etc. are more
>>>> challenging for the garbage collector. I'm writing to ask if someone can
>>>> answer: 1. Is this true, and 2: Why? I can't seem to find anything like a
>>>> writeup or documentation that mentions this. The HeapObjects trac page also
>>>> mentions nothing about these supposed difficulties that GC faces with
>>>> mutable heap objects.
>>>>
>>>> Thanks
>>>> _______________________________________________
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>>>>
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>
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