Re: Concurrent Containers
On 2010-09-01 20:53:37 -0400, Scott Meyers said:
It's too late to change now, I think, but in retrospect I should have
used a subject of "Concurrent Data Structures" for this thread, because
the term "containers" suggests to many people all the usual STL API
stuff, and I'm not married to that API.
I realized after I'd sent my response that that was probably what you
were talking about. But this discussion of the wrong topic is, I hope,
helpful to others.
In fact I'd be surprised if concurrent containers can offer the same
API. Java's ConcurrentHashMap, for example, has a size method that
returns only an approximation of the number of elements in the map,
because, as Brian Goetz puts it in "Java Concurrency in Practice," "the
result of size could be out of date by the time it is computed."
Right. That's the point I was trying to make: that adding concurrency
to existing containers doesn't get you much.
What I'm really interested in is the availability of
already-implemented-and-proven commonly-useful concurrency-friendly
data structure types for C++. One that's been mentioned by more than
one person (other than me) in this thread is a queue,
Yes, that's probably the most obvious one.
and it's probably no coincidence that both TBB and PPL offer
concurrent_queue. They also both offer concurrent_vector and
(apparently) concurrent_unordered_map, which suggests to me that uses
for those types are not particularly difficult to come by.
I haven't looked at those, but in general, those last two sound like
too broad an interface. vector and map are implementation tools, not
design-level tools, and if concurrent_vector and concurrent_map are
what their names suggest, they don't sound like a good idea. Thread
safety has to be designed in at the application level; there's no set
of tools that will make a bad design safe. There are a few things that
are useful on their own, such as a queue, but vector and map have too
wide an interface to be useful as concurrent objects.
--
Pete
Roundhouse Consulting, Ltd. (www.versatilecoding.com) Author of "The
Standard C++ Library Extensions: a Tutorial and Reference
(www.petebecker.com/tr1book)