[Monotone-devel] Fixed netsync-wedging bug

[Graydon Hoare]

Hi,

I just tracked down a subtle and annoying netsync bug that has been 
pestering us for a while. It involves a not-very-hard-to-trigger case 
wherein the nesting of queries and subqueries gets broken. The symptom 
is just netsync going dead awaiting i/o, with no obvious logic errors or 
data corruption.

If netsync has been hanging for you recently (post-0.26), I'd be curious 
to hear feedback on whether this change fixes your problems. The head 
containing a merge of my change is

502422b06d27c0bd826d4ace41ad433cec2c1256

I also added a randomizing unit tester for the netsync refiner (which is 
what isolated the bug, actually) so this sort of thing should be 
slightly more readily caught in the future.

-graydon