[packagekit] The dbus backend

[Robin Norwood]

On Mon, 11 Feb 2008 23:28:06 +0000
Richard Hughes <hughsient at gmail.com> wrote:

> rnorwood and I have been working on the yum2 dbus backend. I've
> actually got the yum2 backend to run now, with search times down from
> 3 seconds to 0.7 seconds. So quite a dramatic speedup. Good stuff to
> look forward to.

Wait, it works?  Hey, it works!  Neat!  It wasn't working at all for me
until I read your message and tried again.  I guess dbus just needed to
think about things for a bit.

> What I really want to do is emit the enumerated values up the stack as
> numeric types. This poses a problem for python I think:
> 
> enum.py:
> STATUS_CANCEL = "cancel"
> STATUS_CLEANUP = "cleanup"
> 
> yumDBUSbackend.py:
> ...
>     self.StatusChanged(STATUS_WAIT)
> ...
>     @dbus.service.signal(dbus_interface=PACKAGEKIT_DBUS_INTERFACE,
>                          signature='u')
>     def StatusChanged(self, status):
>         print "StatusChanged (%i)" % (status)
> 
> So, the dbus interface is expecting an integer back (corresponding to
> src/pk-common.h) and python is passing back a string, hence boom.
> 
> So we have two ways to do this:
> 
> enum.py:
> STATUS_CANCEL_ID = 4
> STATUS_CLEANUP_ID = 7
> STATUS_CANCEL = "cancel"
> STATUS_CLEANUP = "cleanup"
> 
> yumDBUSbackend.py:
> ...
>     self.StatusChanged(STATUS_WAIT_ID)
> ...
>     @dbus.service.signal(dbus_interface=PACKAGEKIT_DBUS_INTERFACE,
>                          signature='u')
>     def StatusChanged(self, status):
>         print "StatusChanged (%i)" % (status)
> 
> This is the most efficient way, although needs a whole set of new
> constants, although, these are trivially autogenerated using Toms
> magic generator.
> 
> Or, we could just send text and parse the text back into enumerated
> types in the deamon, albeit with a speed penalty.
> 
> There's no API or ABI guarantees for DBUS modules for IPC (shoulnd't
> be built out of tree), so I'm not scared of using raw uint32 numbers.
> 
> So, do we be efficient and pass back integers (risking ABI breakage),
> or do it belt and braces and parse each one in the daemon.
> 
> Comments welcome.

Ok, I don't get it.  Why keep the text at all if you want ints?  Why
not pass everything up the stack as ints, and let the UI translate from
int -> string?

enum.py:
STATUS_CANCEL = 4
STATUS_CLEANUP = 7

yumDBUSbackend.py:
...
    self.StatusChanged(STATUS_WAIT)
...
    @dbus.service.signal(dbus_interface=PACKAGEKIT_DBUS_INTERFACE,
                         signature='u')
    def StatusChanged(self, status):
        print "StatusChanged (%i)" % (status)

Etc.

Or is that basically your idea #1?  If so, I'd go with that, except
I don't see why we need to keep the string version around in an enum at
all, except maybe as a map for display in the UI.

-RN

-- 
Robin Norwood
Red Hat, Inc.

"The Sage does nothing, yet nothing remains undone."
-Lao Tzu, Te Tao Ching