Re: Pool of threads with one producer and several consumers

[Jan Wedekind]

You can use condition variables (together withvthe mutex) to signal 
availability of a new item to consume.

On 17. Juli 2016 12:52:49 GMT+00:00, Amirouche Boubekki <address@hidden> wrote:
>I forgot the attach to the previous mail the full code mocking
>a pool of thread. So here it is.
>
>On 2016-07-17 13:51, Amirouche Boubekki wrote:
>> Héllo guilers!
>> 
>> This is more like system programming question, but hopefully someone
>> will enlighten me.
>> 
>> I'd like to create a pool of thread with one producer and several
>> consumers. This needs comes from the need to make my database server
>> multithread. The flow of the program I imagine is the following:
>> 
>> 1. The client application need to do a query against the database
>> 
>> 2. The client open a connection against the server
>> 
>> 3. The client send the query
>> 
>> 4. The server's main thread accept a new connection
>> 
>> 5. The server dispatch the connection to consumer threads
>> 
>> 6. The consumer thread reads the query, execute it, returns the
>result
>>    and close the connection
>> 
>> The point I'm trying to solve is the point 5, when the server main
>> thread receive a new connection it must send the new connection to
>one
>> of the consumer.
>> 
>> My first idea was to create a queue protected by a mutex. The
>> protected queue will be used:
>> 
>> - by the mainthread to produce new connections for consumers
>> 
>> - by the consumers to retrieve connections
>> 
>> I translated this into Guile as follow:
>> 
>> ```
>> (define (make-handler queue mutex init proc)
>>   (lambda () ;; thread thunk
>>     (init)  ;; thread initilisation
>>     (let loop ()  ;; thread loop
>>       (lock-mutex mutex)  ;; try to pick a connection
>>       (if (not (empty? queue))
>>         (let ((item (pop! queue)))  ;; pick a connection
>>           (unlock-mutex mutex)
>>           (proc item))  ;; process connection
>>         (unlock-mutex mutex))  ;; XXX: else, there is nothing in the 
>> queue.
>>                                ;;      In theory I must put a sleep 
>> here, right?
>>       (loop))))
>> ```
>> 
>> AFAIU, sleep'ing is not a good thing to do. So I am investigating how
>
>> to use
>> select or epoll instead. But i'm not sure how this should happen.
>> 
>> Any ideas?
>> 
>> NB: Right now, I don't plan to have persistent connections. What I
>> mean is that once a query is executed the connection to the client is
>> closed. If you have idea on how to use persistent connection, I am
>> also interested.
>
>-- 
>Amirouche ~ amz3 ~ http://www.hyperdev.fr

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