From: Mark Walters <markwalters1009@gmail.com>
To: Justus Winter <4winter@informatik.uni-hamburg.de>, notmuch@notmuchmail.org
Subject: Re: [PATCH 1/7] Split notmuch_database_close into two functions
In-Reply-To:
 <1332291311-28954-2-git-send-email-4winter@informatik.uni-hamburg.de>
References:
 <1332291311-28954-1-git-send-email-4winter@informatik.uni-hamburg.de>
	<1332291311-28954-2-git-send-email-4winter@informatik.uni-hamburg.de>
User-Agent: Notmuch/0.12+88~gb9fb613 (http://notmuchmail.org) Emacs/23.3.1
	(x86_64-pc-linux-gnu)
Date: Sat, 31 Mar 2012 18:17:15 +0100
Message-ID: <87fwcopu5g.fsf@qmul.ac.uk>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Precedence: list

Justus Winter <4winter@informatik.uni-hamburg.de> writes:

> Formerly notmuch_database_close closed the xapian database and
> destroyed the talloc structure associated with the notmuch database
> object. Split notmuch_database_close into notmuch_database_close and
> notmuch_database_destroy.
>
> This makes it possible for long running programs to close the xapian
> database and thus release the lock associated with it without
> destroying the data structures obtained from it.
>
> This also makes the api more consistent since every other data
> structure has a destructor function.

I like the idea of this series but have two queries before reviewing it.

The first is a concern that if we change the library functions we should
update the library version otherwise out of tree users won't know which
to call. (I don't actually know how versioning is done but I think we
should at least be able to make new out-of-tree code cope with the old
or new version). It might be worth keeping notmuch_database_close as it
is for now and adding something like notmuch_database_weak_close with
the new functionality. Then whenever the library version is next going
to get bumped we could move to the destroy/close nomenclature.

Secondly, I think the patch series could be made clearer and easier to
review. If you do it in three steps

1) change of notmuch_database_close to notmuch_database_destroy (just
   the function name change)
2) split the new notmuch_database_destroy into two as in the current
   first patch
3) Make any changes (if there are any) of notmuch_database_destroy to
   notmuch_database_close.

The advantage is that the first change is easy to test (essentially does
it build) and then changes from notmuch_database_destroy to
notmuch_database_close in step 3 are explicit rather than the current
situation where we need to grep the code to see if some instances of
notmuch_database_close were not changed to notmuch_database_destroy.

Of course if the decision is to go via the weak_close version then you
just need to do the analogues of 2 and 3.

Best wishes

Mark

>
> Signed-off-by: Justus Winter <4winter@informatik.uni-hamburg.de>
> ---
>  lib/database.cc |   14 ++++++++++++--
>  lib/notmuch.h   |   15 +++++++++++----
>  2 files changed, 23 insertions(+), 6 deletions(-)
>
> diff --git a/lib/database.cc b/lib/database.cc
> index 16c4354..2fefcad 100644
> --- a/lib/database.cc
> +++ b/lib/database.cc
> @@ -642,7 +642,7 @@ notmuch_database_open (const char *path,
>  			 "       read-write mode.\n",
>  			 notmuch_path, version, NOTMUCH_DATABASE_VERSION);
>  		notmuch->mode = NOTMUCH_DATABASE_MODE_READ_ONLY;
> -		notmuch_database_close (notmuch);
> +		notmuch_database_destroy (notmuch);
>  		notmuch = NULL;
>  		goto DONE;
>  	    }
> @@ -702,7 +702,7 @@ notmuch_database_open (const char *path,
>      } catch (const Xapian::Error &error) {
>  	fprintf (stderr, "A Xapian exception occurred opening database: %s\n",
>  		 error.get_msg().c_str());
> -	notmuch_database_close (notmuch);
> +	notmuch_database_destroy (notmuch);
>  	notmuch = NULL;
>      }
>  
> @@ -738,9 +738,19 @@ notmuch_database_close (notmuch_database_t *notmuch)
>      }
>  
>      delete notmuch->term_gen;
> +    notmuch->term_gen = NULL;
>      delete notmuch->query_parser;
> +    notmuch->query_parser = NULL;
>      delete notmuch->xapian_db;
> +    notmuch->xapian_db = NULL;
>      delete notmuch->value_range_processor;
> +    notmuch->value_range_processor = NULL;
> +}
> +
> +void
> +notmuch_database_destroy (notmuch_database_t *notmuch)
> +{
> +    notmuch_database_close (notmuch);
>      talloc_free (notmuch);
>  }
>  
> diff --git a/lib/notmuch.h b/lib/notmuch.h
> index babd208..6114f36 100644
> --- a/lib/notmuch.h
> +++ b/lib/notmuch.h
> @@ -133,7 +133,7 @@ typedef struct _notmuch_filenames notmuch_filenames_t;
>   *
>   * After a successful call to notmuch_database_create, the returned
>   * database will be open so the caller should call
> - * notmuch_database_close when finished with it.
> + * notmuch_database_destroy when finished with it.
>   *
>   * The database will not yet have any data in it
>   * (notmuch_database_create itself is a very cheap function). Messages
> @@ -165,7 +165,7 @@ typedef enum {
>   * An existing notmuch database can be identified by the presence of a
>   * directory named ".notmuch" below 'path'.
>   *
> - * The caller should call notmuch_database_close when finished with
> + * The caller should call notmuch_database_destroy when finished with
>   * this database.
>   *
>   * In case of any failure, this function returns NULL, (after printing
> @@ -175,11 +175,18 @@ notmuch_database_t *
>  notmuch_database_open (const char *path,
>  		       notmuch_database_mode_t mode);
>  
> -/* Close the given notmuch database, freeing all associated
> - * resources. See notmuch_database_open. */
> +/* Close the given notmuch database.
> + *
> + * This function is called by notmuch_database_destroyed and can be
> + * called multiple times. */
>  void
>  notmuch_database_close (notmuch_database_t *database);
>  
> +/* Destroy the notmuch database freeing all associated
> + * resources */
> +void
> +notmuch_database_destroy (notmuch_database_t *database);
> +
>  /* Return the database path of the given database.
>   *
>   * The return value is a string owned by notmuch so should not be
> -- 
> 1.7.9.1
>
> _______________________________________________
> notmuch mailing list
> notmuch@notmuchmail.org
> http://notmuchmail.org/mailman/listinfo/notmuch