Is content locking needed in the P2P protocol? Based on re-reading
bugs/concurrent_drop--from_presence_checking_failures.mdwn,
I think so: Peers can form cycles, and multiple peers can all be trying
to drop the same content.
So, added content locking to the protocol, with some difficulty.
The implementation is fine as far as it goes, but note the warning
comment for lockContentWhile -- if the connection to the peer is dropped
unexpectedly, the peer will then unlock the content, and yet the local
side will still think it's locked.
To be honest I'm not sure if Remote.Git's lockKey for ssh remotes
doesn't have the same problem. It checks that the
"ssh remote git-annex-shell lockcontent"
process has not exited, but if the connection closes afer that check,
the lockcontent command will unlock it, and yet the local side will
still think it's locked.
Probably this needs to be fixed by eg, making lockcontent catch any
execptions due to the connection closing, and in that case, wait a
significantly long time before dropping the lock.
This commit was sponsored by Anthony DeRobertis on Patreon.
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