Linda is a concept for process communication.
For an introduction and a deeper description, see [Carreiro & Gelernter 89a] or [Carreiro & Gelernter 89b], respectively.
One process is running as a server and one or more processes are running as clients. The processes are communicating with sockets and supports networks.
The server is in principle a blackboard on which the clients can write
(out/1), read (rd/1) and remove (in/1) data. If
the data is not present on the blackboard, the predicates suspend
the process until they are available.
There are some more predicates besides the basic out/1,
rd/1 and in/1. The in_noblock/1 and
rd_noblock/1 does not suspend if the data is not available—they
fail instead. A blocking fetch of a conjunction of data can be done
with in/2 or rd/2.
Example: A simple producer-consumer. In client 1:
producer :-
produce(X),
out(p(X)),
producer.
produce(X) :- .....
In client 2:
consumer :-
in(p(A)),
consume(A),
consumer.
consume(A) :- .....
Example: Synchronization
...,
in(ready), %Waits here until someone does out(ready)
...,
Example: A critical region
...,
in(region_free), % wait for region to be free
critical_part,
out(region_free), % let next one in
...,
Example: Reading global data
...,
rd(data(Data)),
...,
or, without blocking:
...,
rd_noblock(data(Data)) ->
do_something(Data)
; write('Data not available!'),nl
),
...,
Example: Waiting for one of several events
...,
in([e(1),e(2),...,e(n)], E),
% Here is E instantiated to the first tuple that became available
...,