On Thu, Sep 17, 2009 at 9:57 AM, Chouser <chou...@gmail.com> wrote:
>
> On Thu, Sep 17, 2009 at 12:28 AM, Krukow <karl.kru...@gmail.com> wrote:
>>
>> Final question. The docs say that 'ensure' permits more concurrency
>> than promoting the ref to a write. Is there a quick/simple way of
>> explaining how? (Or do I need to go to the source :-)
>
> If you have multiple transactions ensuring the same var but
> no transactions changing it, all those transactions can
> proceed simultaneously.  If they all did dummy writes
> instead of ensure, they could only proceed in order.

Ah ... I think I misunderstood an important part of the question. I
wasn't assuming that all the concurrent transactions were going to use
ensure or a dummy write on the same Ref. So the key is that multiple
transactions can successfully ensure the same Ref, but multiple
transactions cannot successfully write the same Ref.

-- 
R. Mark Volkmann
Object Computing, Inc.

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