This avoids import with --no-content and with --content potentially
generating two different trees, leading to a merge conflict when run in
two different clones of a repo. And it's necessary groundwork to make
git-annex sync --no-content import from special remotes that support
importKey.
Only the directory special remote currently supports importKey, and it
generates the same key as git-annex usually does, so there is no
behavior change for it.
Future special remotes will need to take care when adding importKey,
if it generates different keys. Added some warnings about that to
comments.
This commit was sponsored by Noam Kremen on Patreon.
TVars were not updated atomically, which was ok when each thread got its
own External that was the only thing using these TVars. But, with the
async extension, several External instances can share the same var, so
it needs to be a TMVar to avoid read/write conflicts.
In particular, this makes PREPARE only be sent once.
Moving jobid generation to the git-annex side lets it be simplified a
lot.
Note that it will also be possible to generate one jobid per connection,
rather than a new job per request. That will make overflow not an issue,
and will avoid some work, and will simplify some of the code.
Receive loop looks right. Still need the send loop.
And, a complication is that some messages git-annex
sends need to be wrapped in REPLY_ASYNC, while others
do not. So will probably need to split externalSend
into two.
Now that I've started implementation, I see it's really necessary that
every message the special remote sends use the protocol, otherwise
nasty edge cases abound.
