[tahoe-dev] Lock files in Tahoe directories

[Brian Warner]

> What if all clients are using the same helper to make updated to the  
> shared
> dirs?  Does the internal serialization mentioned in mutable.txt  
> allow the
> helper to ensure that updates are serialized?

Nope, unfortunately the helper only handles immutable uploads. If it  
helped with mutable publishes too, then yeah, that would probably  
cover it. But it doesn't.

(we only implemented one of the four things that a Helper might help  
with, since immutable-download, mutable-publish, and mutable-retrieve  
weren't as important).

I think that a central lock manager is the way to go. A long time ago  
we talked about this, and I think we were planning on storing a FURL  
in the mutable file somewhere, and the rule would be that clients who  
see a FURL there are obligated to contact it and claim a lock before  
starting the read-modify-write sequence. Our RSA mutable-file design  
doesn't leave space for arbitrary extra data, though.. maybe I'll add  
a note to the DSA design notes page about providing extension space  
for the future...

cheers,
  -Brian