[erlang-questions] Enhancing the ETS API

[Jay Nelson]

Recently I have been working on an ets_buffer module that allows
for concurrent updates with multiple readers and writers to a
central queue or stack data structure. Through careful combination
of {write_concurrency, true} and atomic operations with update_counter
it is possible to dramatically improve performance over a strictly serial
gen_server wrapper around normal erlang queues, but the limited
number of atomic mutable operations on ets tables make it difficult
to architect useful data structures safely in ets.

The most glaring missing features are to read and remove an entry
in one operation, and to increment data elements which may be
thresholded by another data element in the same record.

The following commands could be useful with a write_concurrency ets table:

1) ets:match_delete(Tab, MatchSpec, Return_Objects::true) -> [Deleted_Object]
   ets:select_delete(Tab, MatchSpec, Return_Objects::true) -> [Deleted_Object]

    Currently, delete does not return any objects.

2) ets:update_counter(Tab, Key, Cmd)
     where Cmd also allows:

   {Field_Pos, Inc, Thresh, rollback}

     Do not change value, but return existing value if Thresh violated

   {Field_Pos, Inc, {Thresh_Pos}, New_Value | rollback}

     Threshold_Pos refers to another value stored in same record


Anyone else interested in enhancements to the ets interface to allow
more variants on update_counter? Are there other API calls that would
make concurrent mutable data structure operations easier?

jay