notifications support

3.16: adda/notifications:

. after reading about dev.mac's notification system
I'm wondering how adda, too,
can provide this service .
. existing parts of adda should be reused
when possible;
eg, all coprograms having mailboxes .
[3.29: coprograms include all concurrent processes:
coroutines, tasks, type-mgt's,
and other background services .]

multi-level interfaces:
. you can see notifications in action
during a debug watch-point command:
that makes execution stop at
any code that modifies a given obj .
. this is economically possible because of
the multiple levels of interface
where all the high-level entries
use just one low level write function;
so, then an obj's write function
can be replaced with a
(call me instead of writing);
likewise, in the same way that
classes can be subclassed,
objects within the same class can be
individually customized
so as to facilitate notifications .

3.17:
. this can be done while still
reusing class functions
by having every object include
along with a tag
a watched bit for impl'ing notifications .
. the way to identify an object
is that every object
-- even when on the stack rather than heap --
is part of a process with an id#
and then part of a call path:
eg, process#2/sub1/sub2
. or,
every object is part of an act'rec ...
(this needs a proof,
but the future looks bright);
anyway,
the run-time exec' is checking the watched.bit
during each object access,
and if it's set,
then it's got that obj's id,
which is used to look up the object
in a notification database
to see what about the object is customized .
. the db can provide
the conditions under which
notifications need to be sent out,
and can also keep the list of
which mailboxes should be notified,
or what actions need to occur
if a certain trigger is set .

3.16: addm/notifications:
. assuming every obj has a watched bit
for impl'ing notifications:
. a problem with letting arbitrary obj's be watched
is it brings down performance across the entire system
regardless of how little
the watching feature is used ?
. for obj watching to be efficient,
have 2 versions of addm:
one will be checking the watch bit,
while the other version will ignore it .
. every process has a pointer indicating
which virtual processor it's being run on .