[Pan-devel] A proposal for faster threading.

[Charles Kerr]

I'm thinking of redoing threading so that we can remove the "threading 
articles" step of opening a group and would like to get some feedback on 
the idea:

Right now, Article has a pointer to its parent article and a list of 
children articles. Threading is done in a big pass after a group load, 
so that all the articles are in memory for us to find an article's right 
parent.  The big pass is repeated after an xover.

I'm thinking of moving the parent/child fields out of Article so that 
Article, by itself, won't know who its relations are.  A new, second 
struct will hold that information:

   ArticleNode
   {
      gchar * _message_id;
      Article * _article;
      ArticleNode * _parent;
      ArticleNode ** _children;
   };

So it's a simple tree.  The advantage is that by separating Article's 
fields (subject, date, etc.) from the hierarchy fields (parent, 
children), we can build the latter without the former, and fill in the 
former as we load/xover more headers.

Let's say we get this message:

  Subject: foo
  References: <address@hidden> <address@hidden> <address@hidden>
  Message-Id: <address@hidden>

We look in a Message-ID -> ArticleNode* lookup table for <address@hidden>.
Since it's a new message there's no match, so we create a new Node,
populate it with _article=a and _message_id=<address@hidden>, and add it to the 
lookup table.

Next we start walking backwards through the References: header.
We look for <address@hidden> in our lookup table.  If it's there, we link it
to <address@hidden>.  If it's not there, we create it, populate it with
_article=0 and _message_id=<address@hidden>, add it to the lookup table,
and link it to <address@hidden> anyway.  We repeat for the rest of References:.

Later, if/when <address@hidden> comes in from load/xover, all we have to do is 
set the _article field in the <address@hidden> ArticleNode.

So threading happens progressively, rather than requiring a separate 
step at the end of loading.  Moreover, an article is threaded exactly 
once, rather than once at load and then once per each xover.

This wouldn't affect the header pane, which would filter out empty 
ArticleNodes if it even knew about them at all.

Any thoughts or suggestions?