On Saturday 28 July 2012 02:00:31 Jonathan Nieder wrote:
> Thanks for explaining. Now we've discussed a few different approproaches,
> none of which is perfect.
> a. use --cat-blob-fd, no FIFO
> Doing this unconditionally would break platforms that don't support
> --cat-blob-fd=(descriptor >2), like Windows, so we'd have to:
> * Make it conditional --- only do it (1) we are not on Windows and
> (2) the remote helper requests backflow by advertising the
> import-bidi capability.
> * Let the remote helper know what's going on by using
> "import-bidi" instead of "import" in the command stream to
> initiate the import.
Generally I like your prefered solution.
I think there's one problem:
The pipe needs to be created before the fork, so that the fd can be inherited.
There is no way of creating it if the remote-helper advertises a capability,
because it is already forked then. This would work with fifos, though.
- add a capability: bidi-import.
- make transport-helper create a fifo if the helper advertises it.
- add a command for remote-helpers, like 'bidi-import <pipename>' that makes
the remote helper open the fifo at <pipename> and use it.
- fast-import is forked after the helper, so we do already know if there will
be a back-pipe. If yes, open it in transport-helper and pass the fd as command
line argument cat-blob-fd.
--> fast-import wouldn't need to be changed, but we'd use a fifo, and we get
rid of the env-vars.
(I guess it could work on windows too).
What do you think?
> b. use envvars to pass around FIFO path
> This complicates the fast-import interface and makes debugging hard.
> It would be nice to avoid this if we can, but in case we can't, it's
> nice to have the option available.
> c. transport-helper.c uses FIFO behind the scenes.
> Like (a), except it would require a fast-import tweak (boo) and
> would work on Windows (yea)
> d. use --cat-blob-fd with FIFO
> Early scripted remote-svn prototypes did this to fulfill "fetch"
> It has no advantage over "use --cat-blob-fd, no FIFO" except being
> easier to implement as a shell script. I'm listing this just for
> comparison; since (a) looks better in every way, I don't see any
> reason to pursue this one.
> Since avoiding deadlocks with bidirectional communication is always a
> little subtle, it would be nice for this to be implemented once in
> transport-helper.c rather than each remote helper author having to
> reimplement it again. As a result, my knee-jerk ranking is a > c >
> b > d.
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