Re: threads, queues, and make

On 10/10/2013 04:07 AM, Anne Ogborn wrote:
> I'm writing a logger that runs in it's own thread and communicates via message queues.
> The logger keeps some running statistics. I don't want to assert these for performance reasons,
> so the separate thread is easiest.
> 
> start_logger_thread :-
> message_queue_create(logger_response_queue),
> thread_create(logger_thread,
>      _,
>      [
>  alias(my_logger),
>  detached(true)
>      ]).
> 
>        
> The problem comes in maintaining a pleasant development environment.
> 
> I'd like to continue to have make. update my code happily, but of course the thread and the message
> queue exist, and the system whines when I try to redefine them.
> 
> At the moment I'm just catching the exception, but it'd be better to detect the existance of the queue before creating it. There doesn't seem to be a queue_exists?

message_queue_property/2 can be used for that.  Same for
thread_property/2 to test for the
existince of the thread.  You could also have a log/1 predicate that
creates the thread
lazily.  Something like this (not tested; details may be wrong):

log(Term) :-
	catch(thread_send_message(logger_response_queue, Term),
	      error(existence_error(message_queue, _, _),
	      fail), !.
log(Term) :-
	with_mutex(create_log_thread, start_logger_thread),
	log(Term).

	Cheers --- Jan


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