[MERGE] Convert workingtree.py's use of lock_write to lock_tree_write

[Robert Collins]

On Sun, 2006-09-10 at 19:21 -0500, John Arbash Meinel wrote:
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> Robert Collins wrote:
> > All WorkingTree methods which write to the tree, but not to the branch
> > have been converted to use ``needs_tree_write_lock`` rather than
> > ``needs_write_lock``. Also converted is the revert, conflicts and tree
> > transform modules. This provides a modest performance improvement on
> > metadir style trees, due to the reduce lock-acquisition, and a more
> > significant performance improvement on lightweight checkouts from
> > remote branches, where trivial operations used to pay a significant
> > penalty. It also provides the basis for allowing readonly checkouts.
> > (Robert Collins)
> > 
> > (Hopefully thats self explanatory :)
> > 
> > Next up: anonymous/readonly checkouts.
> > 
> > -Rob
> > 
> ...
> 
> > @@ -195,6 +200,7 @@
> >          builder.merge(interesting_ids=["1"])
> >          self.assertEqual(builder.this.get_file("1").read(), "text4" )
> >          self.assertEqual(builder.this.get_file("2").read(), "hello1" )
> > +        builder.cleanup()
> >          
> >      def test_file_moves(self):
> >          """Test moves"""
> 
> ^- Why all the additions of 'builder.cleanup()'?
> 
> Otherwise +1.

The merge_core tests do branch.pull() - which used to work because
TreeTransform took out a write lock. With TreeTransform taking out
tree_write lock, that pull fails because the branch is read-locked and
we dont support upgrading to write locks from reads. So, MergeBuilder
needs to take out a write lock before the TreeTransform is created
(TreeTransform uses a RAII-like approach locking on construction). This
then leads to failure-to-unlock spew unless the builder is cleaned up
always.

Rob
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