Re: Waiver question

[kilgallen@eisner.decus.org (Larry Kilgallen)]

In article <dewar.862381265@merv>, dewar@merv.cs.nyu.edu (Robert Dewar) writes:
> Richard Kenner said
> 
> <<The problem with these sequences is that they are not atomic.  That
> is that problem that will be remedied on Alpha processors starting
> with EV56.>>
> 
> Of course in Ada they do not *need* to be atomic -- if you waste a bit
> of space to make sure stand alone objects are not too close together,
> and the same in records.
> 
> You don't need to worry about atomic access in any packed structure of
> course, and the standard string type is packed (i.e. it is erroneous
> for one task to store the 3rd charater of a string while another task
> loads the fourth character).

Although a compiler can take care to place separate components
of an unpacked structure into separate quadwords, a programmer
can use representation clauses to bring them back together. If
a programmer uses representation clauses that is an implicit
declaration that they know what they are doing, so compiler
warnings seem inappropriate.

But programmers often do not know what they are doing. Alpha
programs often have code which does not properly handle atomicity,
and until recently even VMS had at least one such piece of code
(not written in Ada) of which I am aware.

Larry KIlgallen