208     def linearize(self, ixs):

   209         '''linearize and topologically sort a list of revisions

   210 

   211         The linearization process tries to create long runs of revs where

   212         a child rev comes immediately after its first parent. This is done by

   213         visiting the heads of the given revs in inverse topological order,

   214         and for each visited rev, visiting its second parent, then its first

   215         parent, then adding the rev itself to the output list.

   216         '''

   217         sorted = []

   218         visit = list(self.headsetofconnecteds(ixs))

   219         visit.sort(reverse=True)

   220         finished = set()

   221 

   222         while visit:

   223             cur = visit.pop()

   224             if cur < 0:

   225                 cur = -cur - 1

   226                 if cur not in finished:

   227                     sorted.append(cur)

   228                     finished.add(cur)

   229             else:

   230                 visit.append(-cur - 1)

   231                 visit += [p for p in self.parents(cur)

   232                           if p in ixs and p not in finished]

   233         assert len(sorted) == len(ixs)

   234         return sorted

   235