Re: task-safe hash table?

[tmoran@acm.org]

>Functions on protected objects could potentially run in parallel on a
>multi-core CPU. Does anybody know if GNAT does this?
>...
>What about a window in which each task makes, say, n searches. n is the
>window size. All misses are postponed till the window end. At that point
  I tried a simple approach:  Lookup is asynchronous, Insert is Protected.
I ran the test data using Gnat 3.15p on a dual-core Pentium and looking at
the Task Manager CPU usage.  With a small number of large buckets in the
hash - so a lookup scans a rather long list and takes a long time - CPU
usage is around 75% (of the total two CPUs).  So there's overlap.  With a
more reasonable hash with a large number of small buckets, the Protected
overhead is larger relative to the "useful work", and CPU usage goes down
to more like 40% (I presume the missing 10% is probably tallied as System
time in task switching instead of app time).  Since by far the best speed
comes from a large number of small buckets, this approach to doing the job
concurrently is a losing proposition.
  Perhaps a windowing or batching approach such as you suggest would
distribute the Protected overhead over more useful work and make the
concurrent approach faster.  I'll look into that this weekend.