[Bug 1282311] [NEW] [FFe] libclick

[Colin Watson]

Public bug reported:

I initially wrote click in Python in order to be able to get it up and
running quickly.  I still think Python is appropriate for large chunks
of it, particularly the parts that are only run by developers ("click
build", "click chroot", etc.), but it is not ideal to have to go through
Python in resource-constrained environments such as phones.  When we
start up Ubuntu Touch in an ARM emulator, it takes a very long time to
run all the click hooks, which directly affects how quickly we can turn
round CI tests; and I've also heard that various queries from desktop
infrastructure currently made by way of running click as a subprocess
can contribute as much as a second to application startup time.  This is
obviously unacceptable and we need to do something about it.

Not wanting to do a scorched-earth rewrite, my approach to this is to
rewrite hot parts of click in C and expose them as a "libclick" library,
using GObject in order to gain introspection support and thus trivially
have Python bindings available.  This will allow me to translate things
gradually, and in particular it will let me leave the existing rather
comprehensive test suite in place with only minimal adjustments, which
will provide quite good assurance that I haven't broken anything too
seriously.  By itself, it may well not speed things up very much as the
top-level /usr/bin/click program will still be a Python script (at least
for the moment), but we will be able to gain significant improvements to
application startup time shortly afterwards with a few very small
changes to packages such as upstart-app-launch.

I had hoped to have an initial version of this in place well before
feature freeze, and have been coding frenetically over the last week to
try to achieve that.  Unfortunately, the basic query functionality
that's top of the list for libclick requires essentially the whole
interwoven edifice of click.{database,hooks,user}, which is around 1000
lines of Python code, and I'm somewhere north of 3000 lines of
corresponding C code now without being finished yet.  If I were able to
separate out any particularly useful subset of this, I would, but I
don't think it's realistic.  I also don't want to try to rush a landing
given how critical it is to the phone.

As such, I'd like to apply for a feature freeze exception for the work
described here.  Based on my current rate of progress, I expect to have
something worth landing by around the end of next week.

** Affects: click (Ubuntu)
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/1282311

Title:
  [FFe] libclick

Status in “click” package in Ubuntu:
  New

Bug description:
  I initially wrote click in Python in order to be able to get it up and
  running quickly.  I still think Python is appropriate for large chunks
  of it, particularly the parts that are only run by developers ("click
  build", "click chroot", etc.), but it is not ideal to have to go
  through Python in resource-constrained environments such as phones.
  When we start up Ubuntu Touch in an ARM emulator, it takes a very long
  time to run all the click hooks, which directly affects how quickly we
  can turn round CI tests; and I've also heard that various queries from
  desktop infrastructure currently made by way of running click as a
  subprocess can contribute as much as a second to application startup
  time.  This is obviously unacceptable and we need to do something
  about it.

  Not wanting to do a scorched-earth rewrite, my approach to this is to
  rewrite hot parts of click in C and expose them as a "libclick"
  library, using GObject in order to gain introspection support and thus
  trivially have Python bindings available.  This will allow me to
  translate things gradually, and in particular it will let me leave the
  existing rather comprehensive test suite in place with only minimal
  adjustments, which will provide quite good assurance that I haven't
  broken anything too seriously.  By itself, it may well not speed
  things up very much as the top-level /usr/bin/click program will still
  be a Python script (at least for the moment), but we will be able to
  gain significant improvements to application startup time shortly
  afterwards with a few very small changes to packages such as upstart-
  app-launch.

  I had hoped to have an initial version of this in place well before
  feature freeze, and have been coding frenetically over the last week
  to try to achieve that.  Unfortunately, the basic query functionality
  that's top of the list for libclick requires essentially the whole
  interwoven edifice of click.{database,hooks,user}, which is around
  1000 lines of Python code, and I'm somewhere north of 3000 lines of
  corresponding C code now without being finished yet.  If I were able
  to separate out any particularly useful subset of this, I would, but I
  don't think it's realistic.  I also don't want to try to rush a
  landing given how critical it is to the phone.

  As such, I'd like to apply for a feature freeze exception for the work
  described here.  Based on my current rate of progress, I expect to
  have something worth landing by around the end of next week.

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