Re: [SHEPHERD] [PATCH] service: Improve 'service-list'.

[Alex Kost]

Ludovic Courtès (2016-01-25 18:06 +0300) wrote:

> Alex Kost <address@hidden> skribis:
>
>> From f3d21e3ec8a100a966153d03264639ebe48e8872 Mon Sep 17 00:00:00 2001
>> From: Alex Kost <address@hidden>
>> Date: Mon, 25 Jan 2016 11:18:00 +0300
>> Subject: [PATCH] service: Improve 'service-list'.
>>
>> * modules/shepherd/service.scm (service-list): Use
>>   'lookup-canonical-service' on each name instead of removing duplicates
>>   from the final list.
>
> [...]
>
>> diff --git a/modules/shepherd/service.scm b/modules/shepherd/service.scm
>> index f84d1dd..94f2aae 100644
>> --- a/modules/shepherd/service.scm
>> +++ b/modules/shepherd/service.scm
>> @@ -871,12 +871,13 @@ Return #f if service is not found."
>>  
>>  (define (service-list)
>>    "Return the list of services currently defined."
>> -  (delete-duplicates
>> -   (hash-fold (lambda (key services result)
>> -                (append services result))
>> -              '()
>> -              %services)
>> -   eq?))
>> +  (hash-fold (lambda (name services result)
>> +               (let ((service (lookup-canonical-service name services)))
>> +                 (if service
>> +                     (cons service result)
>> +                     result)))
>> +             '()
>> +             %services))
>
> OK, except that we know that SERVICE is necessarily true, because the
> canonical service for NAME is necessarily among SERVICES.
>
> So I would remove the ‘if’ and add a comment explaining the above.
>
> OK with this change?

No, the service is not necessarily true.  When a service has several
names (e.g., "root" and "shepherd"), then %services table will contain 2
entries (with 'root' and 'shepherd' keys and the same (#<<service> …>)
value).  So for one of the hash-table entries:

  (lookup-canonical-service 'root (list root-service))

returns #t, and for the other:

  (lookup-canonical-service 'shepherd (list root-service))

it returns #f.

-- 
Alex