[m-rev.] for review: thread safe mutables (part 2)

[Peter Wang]

On 2006-08-29, Julien Fischer <juliensf at csse.unimelb.edu.au> wrote:
> 
> Estimated hours taken: 12
> Branches: main
> 
> Make the get and set operations for non-constant mutables thread safe.  (The
> get operation for constant mutables is thread safe by definition.)  The
> source-to-source transformation for (non-constant) mutables is modified as
> follows: we introduce four primitive operations: unsafe_get, unsafe_set, 
> lock and unlock.

I think there's a problem with this.  This code no longer compiles:

    :- mutable(localsupp, random.supply, random_init(0), mostly_unique,
	[attach_to_io_state, untrailed]).

(the important part is the mostly_unique inst)

rand.m:022: In clause for `set_localsupp(in(mostly_unique))':
rand.m:022:   in argument 1 of call to predicate `rand.unsafe_set_localsupp'/1:
rand.m:022:   unique-mode error: the called procedure would clobber its
rand.m:022:   argument, but variable `X' is still live.
rand.m:022:   The goal could not be reordered, because it was impure.
rand.m:022: In clause for `set_localsupp(in(mostly_unique), di, uo)':
rand.m:022:   in argument 1 of call to predicate `rand.unsafe_set_localsupp'/1:
rand.m:022:   unique-mode error: the called procedure would clobber its
rand.m:022:   argument, but variable `X' is still live.
rand.m:022:   The goal could not be reordered, because it was impure.


Also, I'm not sure what backtrackable update of [non-thread-local]
mutables is supposed to mean in the presence of multiple threads.
Probably nothing sane.

Peter
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