From: Mark Walters <markwalters1009@gmail.com>
To: Jani Nikula <jani@nikula.org>, notmuch@notmuchmail.org, amdragon@MIT.EDU
Subject: Re: [PATCH v4 07/11] lib: added interface
	notmuch_thread_get_flag_messages
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Date: Fri, 03 Feb 2012 09:36:29 +0000
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On Fri, 03 Feb 2012 08:48:27 +0000, Jani Nikula <jani@nikula.org> wrote:
> On Thu, 02 Feb 2012 23:24:56 +0000, Mark Walters <markwalters1009@gmail.com> wrote:
> > On Fri, 03 Feb 2012 01:07:59 +0200, Jani Nikula <jani@nikula.org> wrote:
> > > On Thu, 02 Feb 2012 22:27:36 +0000, Mark Walters <markwalters1009@gmail.com> wrote:
> > > > On Thu, 02 Feb 2012 23:55:33 +0200, Jani Nikula <jani@nikula.org> wrote:
> > > > > 
> > > > > Hi Mark -
> > > > > 
> > > > > This is my first look at any version of the series; apologies if I'm
> > > > > clueless about some details... Please find some comments below.
> > > > > 
> > > > > BR,
> > > > > Jani.
> > > > > 
> > > > > 
> > > > > On Thu,  2 Feb 2012 17:43:35 +0000, Mark Walters <markwalters1009@gmail.com> wrote:
> > > > > > The function is
> > > > > > notmuch_thread_get_flag_messages
> > > > > > (notmuch_thread_t *thread, unsigned int flag_mask, unsigned int flags)
> > > > > > 
> > > > > > and returns the number of messages with the specified flags on flag_mask.
> > > > > 
> > > > > Is the purpose of this function to get the count of messages that have
> > > > > certain flags set, certain flags not set, and certain flags don't-care?
> > > > 
> > > > Yes: I was trying to follow Austin's suggestion from
> > > > id:"20120124025331.GZ16740@mit.edu" (although stupidly I didn't
> > > > follow his suggestion of a function name).
> > > > 
> > > > > At the very least, I think the documentation of the function should be
> > > > > greatly improved.
> > > > > 
> > > > > I think the name of the function should be notmuch_thread_count_messages
> > > > > which is like notmuch_query_count_messages, but for messages in threads
> > > > > (and with some extra restrictions).
> > > > 
> > > > Yes I like your name; before I change it do you (and others) prefer it
> > > > to Austin's suggestion of notmuch_thread_count_flags. Or we could even
> > > > be more verbose with something like
> > > > notmuch_thread_count_messages_with_flags
> > > 
> > > I'd like to make it clear that it's about message count. Not about
> > > getting flags, not about flag counts. _with_flags is a matter of taste,
> > > no strong opinions there.
> > 
> > I think I will go with notmuch_thread_count_messages as you suggest.
> > 
> > > > > >  /* Message flags */
> > > > > >  typedef enum _notmuch_message_flag {
> > > > > > -    NOTMUCH_MESSAGE_FLAG_MATCH,
> > > > > > -    NOTMUCH_MESSAGE_FLAG_EXCLUDED
> > > > > > +    NOTMUCH_MESSAGE_FLAG_MATCH = (1<<0),
> > > > > > +    NOTMUCH_MESSAGE_FLAG_EXCLUDED = (1<<1),
> > > > > > +    NOTMUCH_MESSAGE_FLAG_MAX  = (1<<2)
> > > > > 
> > > > > How are these used by the current lib users at the moment? How will they
> > > > > break with this change?
> > 
> > I will just comment on this: the *only* reason I put in
> > NOTMUCH_MESSAGE_FLAG_MAX was as a way of keeping track of the size of
> > the bitfield. If there is a better way do say!
> 
> At least one improvement would be to make it NOTMUCH_MESSAGE_FLAG_ALL
> (or similar) which would be the OR of all the other flags. Above, it
> should be equal to (1 << 2) - 1. Not only is this something usable to
> the library users, but also more accurate - if I'm not mistaken, the
> flagset array currently has one element too many.
> 
> If documented properly, the users should not be surprised that in the
> future more flags might be added to NOTMUCH_MESSAGE_FLAG_ALL, and
> depending on the case they may or may not want to use that.

I think the current array is the correct size; I do need to keep
track of the number of messages matching no flags, for example to
calculate the total number of messages.

I am not sure of the utility of NOTMUCH_MESSAGE_FLAG_ALL as I think ~0
would give the same result.  I am very happy to add it if others see
some use, and with your earlier suggestions using ARRAY_SIZE etc I would
only have one use of NOTMUCH_MESSAGE_FLAG_ALL+1.

> Some purists might say that #defines are better suited for defining bit
> flags than enums, but I'm fine with either.

I am happy either way.

> 
> > 
> > > > The only existing flag is NOTMUCH_MESSAGE_FLAG_MATCH: that is currently
> > > > zero but in the current code that is the bit offset of the flag; in my
> > > > version it is the actual bit for the flag (otherwise I think flag masks
> > > > end up very ugly). I believe all callers use notmuch_message_set_flag
> > > > and notmuch_message_get_flag so they should not notice the difference.
> > > > 
> > > > > Please align the assignments. 
> > > > 
> > > > Will do.
> > > > 
> > > > > > @@ -457,8 +452,8 @@ _notmuch_thread_create (void *ctx,
> > > > > >      thread->message_hash = g_hash_table_new_full (g_str_hash, g_str_equal,
> > > > > >  						  free, NULL);
> > > > > >  
> > > > > > -    thread->total_messages = 0;
> > > > > > -    thread->matched_messages = 0;
> > > > > > +    for (i = 0; i < NOTMUCH_MESSAGE_FLAG_MAX; i++)
> > > > > > +	thread->flag_count_messages[i] = 0;
> > > > > 
> > > > > memset (thread->flag_count_messages, 0, sizeof(thread->flag_count_messages));
> > > > 
> > > > 
> > > > Will do 
> > > > 
> > > > > >      thread->oldest = 0;
> > > > > >      thread->newest = 0;
> > > > > >  
> > > > > > @@ -473,6 +468,7 @@ _notmuch_thread_create (void *ctx,
> > > > > >  	 notmuch_messages_move_to_next (messages))
> > > > > >      {
> > > > > >  	unsigned int doc_id;
> > > > > > +	unsigned int message_flags;
> > > > > >  
> > > > > >  	message = notmuch_messages_get (messages);
> > > > > >  	doc_id = _notmuch_message_get_doc_id (message);
> > > > > > @@ -485,6 +481,10 @@ _notmuch_thread_create (void *ctx,
> > > > > >  	    _notmuch_doc_id_set_remove (match_set, doc_id);
> > > > > >  	    _thread_add_matched_message (thread, message, sort);
> > > > > >  	}
> > > > > > +	message_flags =
> > > > > > +	    notmuch_message_get_flag (message, NOTMUCH_MESSAGE_FLAG_MATCH) |
> > > > > > +	    notmuch_message_get_flag (message, NOTMUCH_MESSAGE_FLAG_EXCLUDED);
> > > > > > +	thread->flag_count_messages[message_flags]++;
> > > > > 
> > > > > The first impression of using a set of flags as index is that there's a
> > > > > bug. But this is to keep count of messages with certain flag sets rather
> > > > > than total for each flag, right? I think this needs more comments, more
> > > > > documentation. Already naming the field flag_set_message_counts or
> > > > > similar would help greatly.
> > > > 
> > > > I will try and document it better: on first reading I parsed your name
> > > > as flag set (as verb) message counts whereas I assume you mean "flag
> > > > set" as a noun! I will see if I can come up with something though.
> > > 
> > > Yes, as a noun! :)
> > 
> > I haven't come up with a good name: the best I have come up with is
> > flagset_message_count so if you have any suggestions...
> > 
> > > > > >  	_notmuch_message_close (message);
> > > > > >      }
> > > > > > @@ -511,15 +511,28 @@ notmuch_thread_get_thread_id (notmuch_thread_t *thread)
> > > > > >  }
> > > > > >  
> > > > > >  int
> > > > > > +notmuch_thread_get_flag_messages (notmuch_thread_t *thread, unsigned int flag_mask, unsigned int flags)
> > > > > > +{
> > > > > > +    unsigned int i;
> > > > > > +    int count = 0;
> > > > > > +    for (i = 0; i < NOTMUCH_MESSAGE_FLAG_MAX; i++)
> > > > > 
> > > > > ARRAY_SIZE (thread->flag_count_messages)
> > > > 
> > > > ok
> > > > 
> > > > > 
> > > > > > +	if ((i & flag_mask) == (flags & flag_mask))
> > > > > > +	    count += thread->flag_count_messages[i];
> > > > > > +    return count;
> > > > > > +}
> > > > > 
> > > > > I wonder if the same could be accomplished by using two flag mask
> > > > > parameters, include_flag_mask and exclude_flag_mask. I'm thinking of the
> > > > > usage, would it be easier to use:
> > > > > 
> > > > > notmuch_query_count_messages (thread, NOTMUCH_MESSAGE_FLAG_MATCH, NOTMUCH_MESSAGE_FLAG_EXCLUDED);
> > > > > 
> > > > > to get number of messages that have MATCH but not EXCLUDED? 0 as
> > > > > include_flag_mask could still be special for "all", and you could use:
> > > > > 
> > > > > notmuch_query_count_messages (thread, 0, NOTMUCH_MESSAGE_FLAG_EXCLUDED);
> > > > > 
> > > > > Note the name change according to my earlier suggestion. It might be
> > > > > wise to not export the function before the API is chrystal clear if
> > > > > there is no pressing need to do so.
> > > > 
> > > > (I assume you mean notmuch_thread_count_messages.)
> > > 
> > > Doh! Yes.
> > > 
> > > > Can I just check this
> > > > would return the number of messages which have all the flags  in
> > > > include_flag_mask and none of the flags in exclude_flag_mask?
> > 
> > Yes I think this works better: these are the flags I want, these are the
> > ones I don't want seems natural (versus here are the ones I care about
> > and here are the ones of those I want). But I will wait to see if anyone
> > else has an opinion.
> > 
> > > Yes, but only if it makes sense to you! :)
> > > 
> > > > 
> > > > I completely agree about leaving it until we have the API well worked
> > > > out. I wrote it in response to Austin's suggestion and then it looked
> > > > like it would useful in my attempts to remove the
> > > > notmuch_query_set_omit_excluded_messages API. However, those attempts
> > > > failed so it doesn't have any users yet.
> > > > 
> > > > Best wishes
> > > > 
> > > > Mark