[dmd-concurrency] shared arrays

[Sean Kelly]

On Jan 14, 2010, at 1:05 PM, Andrei Alexandrescu wrote:

> Sean Kelly wrote:
>> Earlier, I had been thinking it might be nice to have this though:
>> shared(char)[] a, b;
>> synchronized( lock( a, b ) ) { // some fancy algorithm on a and b }
>> Basically, use the hashtable of mutexes discussed earlier to allow
>> users to obtain locks on a set of N arrays in a safe manner (because
>> expecting them to do it manually will generally result in deadlock).
>> This makes what's happening explicit and allows the whole mess to be
>> handled in library code.  In theory, this same approach could work
>> for any reference type.  The optimization issue would be making
>> gc_query() not need to obtain the GC lock to return a valid result
>> (this may be safe already, I haven't spent the time to figure it
>> out).
> 
> Defining a hashtable of mutexes would be an interesting idea, but it has many aspects we need to think about. One extreme approach would be to always lock a region of memory, not a particular class object. In that case the mutex pointer stored in each class object could disappear, and you'd essentially just say "lock this guy/these guys" and the system would take care of locking the pages in which those guys reside. It might also reduce deadlock risks, but increase contention because of coarser granularity.
> 
> Anyhow, I think it would be quite a rush to go with this for D2.

Yeah definitely.  Since this would be a library thing there's no rush.