[Sugar-devel] One instance activity

david at lang.hm david at lang.hm
Wed Dec 10 05:56:49 EST 2008

On Wed, 10 Dec 2008, Bert Freudenberg wrote:

> On 10.12.2008, at 03:57, david at lang.hm wrote:
>> On Tue, 9 Dec 2008, Bert Freudenberg wrote:
>>> On 09.12.2008, at 18:55, Eben Eliason wrote:
>>>> Are you sure?  Browse makes use of shared code, but still presents the
>>>> user with the appearance of multiple instances.
>>> Right.
>>> The way to do it would be to create a unique D-Bus service in your
>>> activity. When the second instance tries to create that service it
>>> will notice that it already exists. It could then notify its first
>>> instance via said D-Bus service.
>> you don't need to use D-Bus for this, it can be done by X without any other 
>> communication channels.
>> I don't know the details for how to do this, but I've seen mozilla/firefox 
>> do this for a few years. to see this start firefox on one machine, connect 
>> to another machine and point the display back to the first one. then try 
>> and start firefox on that second machine. the end result will be a new 
>> window opening up, but running on the first machine (if you have trouble 
>> seeing the difference, make the two machines have different bookmarks, or 
>> give one network access that the other doesn't have)
>> please don't develop new mechanisms to do things that already exist.
> It's not a new mechanism. The usage of a named D-Bus service to ensure unique 
> program instances is documented and not my invention (though I cannot 
> remember where I saw it first).
> I should have written "One way to do this would be ...", I give you that.
> But you cannot know which way would be preferable for a given activity. And 
> since it is private to the activity and does not affect other activities, no 
> harm is done either way.
> E.g., twiddling X properties is hard in various high-level languages, in 
> particular when using higher-level UI toolkits. Sugar currently requires two 
> custom X properties and this is causing activity authors considerable pain. 
> Even Sugar itself had to resort to C code, adding a custom native library to 
> manipulate these properties, it was not easy in pure Python. This is in stark 
> contrast to the nicely general and easy-to-use Python D-Bus bindings, which 
> are similarly available in other high-level languages.
> So please consider that not all people like having to go down into the 
> machine room to make new plumbing with a C compiler. Having done too much of 
> that myself I can relate to them.

my initial reaction to this is that this sounds like a gap in the python 
libraries that would be very useful to fill. getting someone to write a 
python library to better access the X properties would help many areas.

any idea why nobody has written one yet? Python is much better than many 
languages at letting you write a library in C and then use it cleanly, so 
if doing this in python is as hard as you are indicating, why hasn't it 
been addressed?

David Lang

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