Re: [boost] concurrent_hash_map, RFC

From: Keith Burton (kb_at_[hidden])
Date: 2005-10-16 02:53:13

Given the nice simple definition of the container ( "hashed associative
container that can be used without synchronization from multiple threads" )
, I believe find_and_visit should synchronise despite the breaking the "C
don't pay for what is not used" mantra.
Unless, of course, two functions are provided.

Keith Burton

Peter Dimov wrote:
> A preliminary documentation for a concurrent_hash_map is available:
> 
> http://www.pdimov.com/cpp/concurrent_hash_map.html
> 
> There exists a prototype implementation for that :-) and I'll post it
> online after a bit of cleanup.
> 
> I have a question on the interface that hopefully may be of interest
> to someone. concurrent_hash_map implements the following member
> function: 
> 
> template<class F> bool find_and_visit( K const & k, F f );
> 
> that looks up the element with a key k in the map and, if found,
> invokes f on its associated value. This can be useful in a number of
> situations, but it poses the following problem: what if two threads
> call find_and_visit at the same time with the same k and f modifies
> its argument? Should the map serialize the two calls to f, or should
> it leave the responsibility of ensuring proper synchronization (or
> atomic update, if the mapped_type allows it) to the user?
> 
> Thanks in advance for any comments/opinions on the interface.