Re: Complexity of protected objects

[dmitry@elros.cbb-automation.de (Dmitry A. Kazakov)]

On 2 Mar 2002 17:08:06 -0800, dewar@gnat.com (Robert Dewar) wrote:

>dennison@telepath.com (Ted Dennison) wrote in message news:<4519e058.0202251401.27b95bb0@posting.google.com>...
>> I've generally found that to be good advice. In particular, my PO's
>> always seem to end up just being specialized semaphores or locks, no
>> matter how grandiose I start out planning to make them. Things just
>> work a lot better that way.
>
>This is MUCH too restrictive, it is perfectly reasonable
>to have a large complex data structure as a protected type
>where the operations on it ensure that consistency is
>maintained by doing related updates in a non-interruptible
>manner.

Theoretically, yes. Practically, I have observed the same effect as
Ted Dennison pointed out. There are too many reasons why it does not
work, sigh. One of them is that protected types are not tagged. As a
result, very often one fails to use PO as the base for that large
complex data structore. Instead of that one has a PO with an access
discriminant pointing to some class wide. Slowly but steadily all the
functionality flows into that tagged type and in the end the PO
degrades to a simple lock.

Regards,
Dmitry Kazakov