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Re: [equinox-dev] In which thread are OSGI services started
Lars,

One way to _guarantee ordering_ (in the sense that you are assured something else has already occurred) is by using a _static_ @Reference to a service. The other service must have been "registered" and in terms of DS it would have to also have been activated before you're @Reference would be satisfied (and when static, the reference is only satisfied BEFORE activation).

You can do this even if the other service was not published by DS.

So, if Eclipse early startup has somehow registered some service you could get which would allow you to detect a state you're be ok to run AFTER then your OSGi service would be forced to wait on it using the approach above.

There are many use cases like this. In fact the OSGi Alliance is working actively on a Condition Service Specification which is precisely this kind of "do something when condition X is satisfied" type of thing.

- Ray

On Wed, Sep 4, 2019 at 2:51 PM BJ Hargrave <hargrave@xxxxxxxxxx> wrote:
The DS specification says nothing about what thread a DS component's method is invoked upon. It may be someone else's thread or a thread that SCR manages in an executor. But as a component implementer you MUST NOT assume anything about the thread upon which your component's methods are invoked. (Other than it is not your thread to use for long periods of time.)
--

BJ Hargrave
Senior Technical Staff Member, IBM // office: +1 386 848 1781
OSGi Fellow and CTO of the OSGi Alliance // mobile: +1 386 848 3788
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----- Original message -----
From: Lars Vogel <lars.vogel@xxxxxxxxxxx>
Sent by: equinox-dev-bounces@xxxxxxxxxxx
To: Equinox development mailing list <equinox-dev@xxxxxxxxxxx>
Cc:
Subject: [EXTERNAL] Re: [equinox-dev] In which thread are OSGI services started
Date: Wed, Sep 4, 2019 14:44
 
Thanks Neil and BJ. What if I use OSGi ds (Felix) to define the service? 
 
 
Best regards, Laes
 
Neil Bartlett <njbartlett@xxxxxxxxx> schrieb am Mi., 4. Sep. 2019, 14:44:
Short answer is that you should not make any assumption about the thread that your component is activated.
 
Long answer is that for an immediate component, it is likely to be activated in whichever thread called Bundle.start(). For a lazy service component, it is likely to be activated in whichever thread called BundleContext.getService().
 
But the outcome is the same. You are always "borrowing" a thread and should never do long running work in the activate method of a component. If you have any such work to do, then you should spin it out as a thread or submit it to an executor service.
 
Neil
 
On Wed, 4 Sep 2019 at 13:41, Lars Vogel <lars.vogel@xxxxxxxxxxx> wrote:
Friends of Equinox,

If I create an immediate OSGi service, in which thread is it created?
How about lazy OSGi services?

The background of my question is that I would like to replace an
Eclipse early startup extension with an immediate OSGi but I'm not
sure if that would block the main thread until the service has been
created.

Best regards, Lars

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