D array expansion and non-deterministic re-allocation

[Steven Schveighoffer]

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).  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...

-Steve