[Openembedded-architecture] Bitbake server rework

[Richard Purdie]

I just wanted to give people a heads up that a pretty significant
change in bitbake's internal behaviour has merged.

In short, the server backend to bitbake has been reworked and bitbake
now always forks off a "cooker" or server process (if needed) and then
connects to it using a unix domain socket.

The xmlrpc and process server backends are replaced with one unified
interface where there is always a process server which can optionally
provide an xmlrpc interface for remote connections.

This means you get "memres" behaviour simply by setting
BB_SERVER_TIMEOUT to some positive value and then the cooker will
remain around for that length of time before unloading from memory.

Right now, the default is 0 giving the same behaviour as before, with
the change that the cooker is always an independent process.

BB_SERVER_TIMEOUT being non-zero is known to break some oe-selftests
right now, that is some we can start to address now we have the code
baseline merged. It does seem to work well in normal use although the
internal server resets for new connections may need optimisation too.

I do expect we may have some teething issues with this as its a major
change to the way we've done things. I (and other bitbake developers)
do believe this is the best way forward for the project though and now
is the best time to merge this and get people using it. Not least, it
replaces a load of horrible code nobody really understood with
something simpler and more understandable and capable. I am delaying M2
a little to ensure we get this in now and have time to fix issues
before 2.4.

Cheers,

Richard