Desktopcouch service should be started in background

[Roman Yepishev]

r55 (ui-misc-beautification branch)

It is possible for Devices list to be stuck in "Loading".
STR:
1. Click on any tab that triggers a DBus request
2. Quickly click on "Devices" tab.

Sometimes it is sufficient to doubleclick "Devices" tab (with 0.5-1s interval) for it to stuck in Loading state.

Workaround: Click on some other tab, wait for a bit then return to Devices tab. The "Loading..." label may be replaced by "Value Could not be retrieved" but it is an otherwise functional tab.

This effect can be seen @ http://ubuntuone.com/p/Zm3/

[Roman Yepishev (rye)]

This time it took more attempts to hang. Upon the exiting the application the "Loading..." label was still displayed on the form for about 30 seconds.

[Natalia Bidart (nataliabidart)]

The original report is caused by visiting the 'Services' tab and then going to other tab. The backend is being blocked on desktopcouch starting too slow.

[Roman Yepishev (rye)]

Naty, since desktopcouch originally intended to be started using DBus (and then it got reverted to direct access since DBus call from within desktopcouch to itself was causing deadlock), we may just do a getPort() call to desktopcouch over dbus and establish dbus listener when port is returned. Once the method returns, desktopcouch should be available.

[Natalia Bidart (nataliabidart)]

Roman,

thanks for the suggestion but I'm not sure what you're referring to. Right now we're using the ReplicationExclusion service to query the replication exclusion list, and never using dbus to access desktopcouch.

[Roman Yepishev (rye)]

Naty,

I wrote my message before i talked to Chad about the way python desktopcouch now communicates with "desktopcouch server". It is not done directly but here's the thing: Ubuntu One control panel expects desktopcouch exclusion service to be available right away as there is no callback mechanism to find out when desktopcouch has actually started. At the same time there is one dbus method that ubuntuone control panel can call in async mode to find out when desktopcouch is actually ready thus not blocking the UI.
So it will be something like this:
couchdb = bus.get_object('org.desktopcouch.CouchDB', '/')
couchdb.getPort(reply_handler=backend_method_to_signal_about_desktopcouch_readiness,
                               error_handler=backend_method_to_signal_about_desktopcouch_brokeness)

In this case backend will not be blocked.

[Natalia Bidart (nataliabidart)]

Hi Roman,

thanks for the very specific answer!

[Natalia Bidart (nataliabidart)]

Lowering priority since currently this is not being a blocking issue.