On 05/28/13 15:07, Mike Duigou wrote:
Hi Chris & Doug;
- I don't see the advantage to exposing the ConcurrentHashMap.KeySetView type
particularly for newKeySet(). Why not return Set<K>? The additional methods
don't seem to offer much that's desirable for the newKeySet() case.
Since we don't have a ConcurrentSet interface, people are reduced to
instanceof checks to see if they have a concurrent one. But without
exposing the class, they couldn't even do this, so complained. This
will arise more frequently with j.u.streams.Collectors.
- I am reluctant to deprecate contains(Object) here unless we deprecate it in
Hashtable as well. I recognize that this has been a source of errors
(https://issues.apache.org/bugzilla/show_bug.cgi?id=48755 for one example).
Is it time to deprecate it there as well?
Sure, but why bother. Anyone still using Hashtable is not going to care
if they get more deprecation warnings :-)
- I think there could be more complete description of the
parallelismThreshold and interaction with common pool. i.e. does "maximal
parallelism" mean one thread per element or "size() /
getCommonPoolParallelism()". Some advice for choosing in-between values would
be good unless "1" is the best advice for cases where you just don't know. It
would be a shame to see people shooting themselves in the foot with this.
Changed to:
* <p>These bulk operations accept a {@code parallelismThreshold}
* argument. Methods proceed sequentially if the current map size is
* estimated to be less than the given threshold. Using a value of
* {@code Long.MAX_VALUE} suppresses all parallelism. Using a value
* of {@code 1} results in maximal parallelism by partitioning into
* enough subtasks to utilize all processors. Normally, you would
* initially choose one of these extreme values, and then measure
* performance of using in-between values that trade off overhead
* versus throughput. Parallel forms use the {@link
* ForkJoinPool#commonPool()}.
*
I'd rather not explicitly mention here any particular values for people
to try, since any number we might put is likely to be misused.
Sometime, we should write up a little how-to document about
tuning parallelism separately.
-Doug
