D array expansion and non-deterministic re-allocation
Andrei Alexandrescu
SeeWebsiteForEmail at erdani.org
Tue Nov 24 09:46:37 PST 2009
Steven Schveighoffer wrote:
> On Tue, 24 Nov 2009 11:41:17 -0500, Steven Schveighoffer
> <schveiguy at yahoo.com> wrote:
>
>
>>> The cache is a thread-local map from pointers to size_t. Using it
>>> does not require any locking I think.
>>
>> When reallocating, do you not also need to update the allocated length
>> in the heap, even if the allocation fits into the same block to
>> prevent other threads from stomping? Doesn't that require a lock?
>> Somewhere you have to share the allocated length between threads
>> sharing the same array. I assumed it was going to be in the MRU cache...
>
> If all this is true, I had another thought for an MRU cache. It could
> simply be a map of pointers to the right blocks in the GC that store the
> lengths (to avoid the block search with the global mutex locked).
That's a great idea. I keep on dreaming someone will implement all this
stuff we talk about :o).
> Lookup should be atomic without locking (I think, simply an integer load
> right?), but you'd have to lock to actually do an append.
>
> I don't think we solve the lock problem without having multiple heaps...
I don't think we need to worry about optimizing growth of shared arrays.
Andrei
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