[sugar] python activities startup

[Tomeu Vizoso]

Hi,

as we all know, activities that use the python API (most of them) start
up very slow in the XO, a trivial one launching in 7 seconds.

http://dev.laptop.org/ticket/5228

I don't know yet if performance work will land in update.2 or in
update.3, but now may be a good moment to summarize what we know and see
which are our options.

By the data in #5228, looks like more than 50% of time is spent
importing modules. dbus, telepathy and pygtk make for more than 30% of
_total_ startup time.

In that ticket is attached a file that lists the 161 modules imported at
startup. I doubt most of those modules are actually used during startup,
and many won't be used neither during the activity lifetime, they are
just imported because one module we actually use *may* need it at some
point.

It's clear that we would prefer to not pay this price upfront at
startup, but rather that the needed initializations happened during
runtime as (if) needed.

I would like to take the chance to ask to Guido what's his opinion on
this, as I'm sure this has been discussed in the python community at
some point. How could we move all these initializations from import time
to use time?

I see the following options:

- Reduce the number of things that are done at startup. We probably
could write to the datastore, initialize sharing and creating the D-Bus
service at a later point after startup. These changes look to me as
quite invasive and somewhat risky. The benefit from the user point of
view is not clear, as we would like those things to happen as soon as
possible after the activity window has been brought up.

- Modify the modules that do significant initializations at import time
so that code is executed lazily as needed. Those modules will be inside
python itself, dbus, pygtk, telepathy, sugar, etc. The drawback of this
approach is that we'll need to maintain forks for some time.

- Hack the import logic in python so that the module-level code is
executed only when some function or method from that module is called or
a variable is set. I'm not sure if this is possible by just using the
existing hooks or if we would need to patch python. In case this brings
some incompatibilities, we could activate this "fast mode" through some
flag.

I wonder too if python 2.6 and 3.0 will bring some improvement in these
areas?

Thanks,

Tomeu