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Linda--Process Communication

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
       ...,