On Mon, 29 Nov 2010 11:44:23 -0500, dsimcha <[email protected]> wrote:
== Quote from Steven Schveighoffer ([email protected])'s article
On Mon, 29 Nov 2010 10:58:05 -0500, dsimcha <[email protected]> wrote:
> == Quote from Steven Schveighoffer ([email protected])'s article
>> On Wed, 17 Nov 2010 12:09:11 -0500, dsimcha <[email protected]>
wrote:
>> > == Quote from Steven Schveighoffer ([email protected])'s article
>> >> The issue is that if you append to such an array and it adds more
>> pages
>> >> in
>> >> place, the block length location will move. Since each thread
caches
>> >> its
>> >> own copy of the block info, one will be wrong and look at array
data
>> >> thinking it's a length field.
>> >> Even if you surround the appends with a lock, it will still cause
>> >> problems
>> >> because of the cache. I'm not sure there's any way to reliably
>> append
>> >> to
>> >> such data from multiple threads.
>> >> -Steve
>> >
>> > Would assumeSafeAppend() do the trick?
>> >
>> No, that does not affect your cache. I probably should add a
function
>> to
>> append without using the cache.
>> -Steve
>
> How about using std.array.Appender? This looks safe as far as I can
> tell, but I
> want to make sure there aren't any obscure implementation details that
> would
> prevent this from working, too.
That should be fine, std.array.Appender does not affect the LRU cache.
In
fact, if you try to do normal appending to an array built with Appender,
it will automatically reallocate because the memory does not have the
APPENDABLE bit set (new GC bit I added to avoid misinterpretations).
This is a good solution.
-Steve
Sounds like a good solution to me, too. As long as this situation is
unlikely to
change in the future, I think we should scrap the idea of making
appending to
__gshared using ~= safe with manual synchronization,
I think it's worth giving people who want low-level access to the runtime
functions the ability to avoid using the LRU cache. The cache is meant to
support everyday coding, but can possibly cause problems if you are
interested in doing low-level optimizations.
BUT the following needs to be
documented:
1. Due to obscure implementation details, it is **not** safe to append
to a
non-shared array even if you synchronize manually.
I think you meant __gshared, not non-shared. It's perfectly safe to
append to non-shared arrays.
-Steve
