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Comments on OSGi <comments />


Neil Bartlett said ...

In the introduction you appear to be asking to be enlightened about OSGi, but then you go on to attack it from a position of ignorance and with heaps of bad attitude. Sorry but this is not the way to engage with people when you're asking for help.

If you have some specific questions about how or why OSGi works the way it does, then I and many others will be delighted to help you on the osgi-dev mailing list. Unfortunately this particular page is little more than a rant and can't be the basis for useful discourse.

--Neil Bartlett 00:07, 20 November 2011 (CET)

Hello Neil, thanks for your comment. Yes, you are right, the page is unlikely good start for a useful discourse. On the other hand, it nicely illustrates my frustration with OSGi. Still, I'd be glad to be enlighten about the design misconceptions.

--JaroslavTulach 10:02, 21 November 2011 (UTC)

Mirko Jahn said ...

First of all, I agree that OSGi is not perfect. In fact I do not know any technology that reached some sort of complexity that doesn't have its flaws. I guess that's nature. However, I think you're missing some background/ experience in the underlying concepts and frameworks you're referring too.

First of all, start/stop of a bundle. Here it is important to distinguish between a mere library and a state aware module. For libraries it is perfectly fine to not have an initialization (static initialization is fine here as well, but no "object" related one). In the OSGi world you then do not need to create an Activator. For all modules that are in fact state aware or need some sort of initialization (like Service dependencies), you could create you Activator (or use a declarative way of expressing that). In case a module does not comply with this contract this is a bug in the bundle code. As a general rule, you only expose API's and provide the instances as services, as long as the bundle is not started, no services will be available and no harm is done. Of course there is the "ugly" overhead of needing to know what bundles need to be started and which don't (you could also start all of them - no overhead in case of library bundles, because they won't execute any code). This seems not entirely clean as an approach, but it is powerful. Just imagine you have one bundle providing the API and a simple default service with the implementation. Once you realized the implementation is not good enough, you could just go ahead, reuse the API and not the exposed service (simply do not start the bundle) and provide your own bundle implementing the service in a way you require it.

Second, stopping order. There is an order in which bundles are stopped and they are stopped in the reverse order they were actually started, so what you saw might be a timing issue or an error in the implementation. Also Eclipse is not a perfect OSGi citizen. They did a lot to improve that but they are still not there. For instance many bundles still do not use the service registry, but a more static eclipse specific construct that has flaws with the dynamism of OSGi. I guess this might explain the problem you were experiencing. Also when done correctly (with services), a stopped bundle would not expose the service any longer and the bundle consuming such service would be able to call such bean (because it wouldn't find it) - no harm could be done here. Unfortunately the developer has to account for that or us a framework that does it for him like BluePrint for instance.

Range dependencies are tricky, I agree. Also the approach on handling the correct version, updating handles in the container, refreshing the wiring between bundles. All that is not trivial and error prone. However, I haven't seen anything even close to what is possible with OSGi. You could by designing the exposed and consumed packages correctly, a powerful and future prove API. Implementers know base on version changes when they have to take a closer look (minor version change) and simple service consumers can rely on the major version as an indicator that something might have changed that they should be aware of. Especially with many modules, keeping track of changes is hell. With such ranges, it at least gives you a way to better track where to look and what to adapt in case something happens. This is still not perfect and I am not sure there is a silver bullet at all, but it's the best thing I've seen so far.

To summarize what I am trying to say. OSGi, like many other specs, is not perfect and there might be a better one in the future, but for the time being, it is pretty good and well thought through. Unfortunately the concepts are not simple and certainly not easy to adhere. Especially with the latest version 4.3, many improvements have been done to make it easier and remove potential for errors, but like every complex system, one first has to know it to fully appreciate it. ;-)

--Mirko Jahn 19:59, 23 November 2011 (CET)

A comment by Jesse Glick left at bug 205019

I think this is a bit off the mark. Seems like Eclipse is not really using OSGi as designed. Proper OSGi bundles are (acc. to spec) supposed to work regardless of what other bundles have or have not been started; that is why dynamic services exist, and why bundles are not started in topological order. In other words, we are working around misdesign in Eclipse, not OSGi per se. The problem presumably does not affect Eclipse and its RCP apps because they are not attempting to load code from an arbitrary compliant OSGi container, and so can make assumptions about runtime behavior not guaranteed by the spec.

--Jesse Glick 14:00, 23 November 2011 (CET)

Reply to Mirko's Post

Hello Mirko, first of all - thank you for your time to write down such a long post here. I value your effort.

"I agree that OSGi is not perfect" - sure, I know that NetBeans Runtime Container is not perfect either. Over years in production you just have to come up with a lot of compromises which, when looking backward, may not seem perfect.

"distinguish between a mere library and a state aware module" - yes, I am aware that nobody needs to use Activator - however that is not the problem. I am puzzled by OSGi allowing to load classes from modules with Activator which has not been called! What kind of strange idea is that? In my opinion the fact that I provide an Activator should mean that whenever somebody wants to use me (e.g. activate me), I want that Activator to be called. Why this is not true in OSGi?

"ugly overhead of needing to know what bundles need to be started" - actually this may be the problem. NetBeans is worshiping so called Injectable Singletons. In this use-case, what ever API you link against means that the API is ready to work and is fully configured. The way Eclipse is using Activators violates this (which may be Eclipse fault as Mirko and Jesse indicate). You say "simply do not start the bundle" - sure, this is what works in NetBeans as well if you don't need a module with implementation of an API, just don't enable it. But still, I don't understand why there is the dichotomy between using and starting a bundle. To allow an API to be bundled with its implementation that is registered in Activator (so others can use the API without the implementation)? That sounds weird!

"reverse order they were actually started" - see, I did not know this. But then the problem is the start order. Obviously, those bundles with as less dependencies as possible, should be started first. However I understand the OSGi may have problem - there does not seem to be a bulk start operation. One can start just a single bundle, not a set of bundles. In NetBeans Runtime Container one just asks to enable a set of bundles and the system starts them in the correct order. The system always guarantee Activators are called on modules needed by somebody. Sounds like a deficiency in OSGi where determining the start order is fully left in hands of poor users of the OSGi API.

"Range dependencies are tricky" - RangeDependencies don't really belong into my most recent rant, but there are issues associated with them - althrough they may be mitigated to avoid NP-Complete problems.

"certainly not easy to adhere" - if a concept is not easy to adhere, then the system is not designed for clueless use. And that is a problem as most of us are completely clueless when using others APIs. Should we threat OSGi as an assembly language for modularity hoping somebody will wrap it with higher level concepts? That would support my conclusions - OSGi helped us see the value of modularity, but proper, widely used modularity should rather not expose OSGi at all.

--JaroslavTulach 18:23, 24 November 2011 (UTC)

Tristen said ...

why can't you make all 3 choices at once:-Save Page as MHTML-save html-save whole paghwey ony MHTML or only 2 last variants?

--Tristen 20:53, 25 June 2013 (CEST)

Meganedos said ...

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--Meganedos 01:46, 26 June 2013 (CEST)

Reinold said ...

Thanks, yeah, that was pretty much my point. I don't see how a new color being avalaible would spur buyer's remorse. If you hated the colors avalaible you wouldn't have bought the thing, I'm assuming. After that, what's the big deal?As far as a price drop, I was playing a bit of Michael Pachter there. There's higher potential for a price drop sooner than later because of the PSV, due to lukewarm 3DS sales and the unexpected competitive pricing of the Sony product spurring the sudden announcement of a new color pushing up the timetables. I find it hard to believe they'd announce a new color this quickly of their own volition. That's what they do, right? That's why the Wii and DS Lite were only avalaible in white for like the first 2 years or however long it took (seemed like forever), because they were selling gangbusters and there wasn't a need to kickstart sales yet with a new edition.No attempt at flamebait, and I do have a smartphone, which is why I don't have a pony in this race. I'm speaking strictly as an observer. :) If you're happy with your handheld that's all that shouldn't matter, and it shouldn't bother you that I don't care one way or the other.

--Reinold 08:12, 26 June 2013 (CEST)

Allie said ...

Of course, that's an itenrtsnieg point, which makes this exchange of interpretations rewarding.(On the side: From a deployment perspective, everything is a bundle. Because the plugins' folder has a history tied to the original Eclipse modularity system, the name of that folder is confusing. And perhaps a candidate for a change request.Historically, the adoption of OSGi has introduced a level of blurring which makes this discussion fairly complicated. The adoption introduced an overlap in functionality, as there are now different programming patterns available to contribute' or to extend'. As it stands today, the framework taps into those different layers at the same time, creating a mix which lies at the heart of this discussion, I think.Categorizing bundles, for example as a higher-level type such as a plug-in', has become debatable because a bundle can contain a mix of fingerprint meta-data: OSGi declarative services, plugin.xml Eclipse extensions, .Still, I find that sentences like mixing bundles and plug-ins' are still valid given the specific nature of the layers in the framework. Apart from meta-data content in the bundle, there are also life-cycle aspects to consider. I do consider the framework to have become a mix of both: bundles en plug-ins.There is enough to distinguish, enough to warrant that both names remain in existence. Unfortunately, as they are related', making the distinction in some cases is like separating Siamese twins, in which case only some convention helps to make the call. But because sometimes the distinction is clear-cut, I can't help feeling that we will never be able to use a single blanket term.

--Allie 19:44, 26 June 2013 (CEST)

Vikas said ...

I could suggest some IDE's or editros, but it's all personal preference. Some people like to use vim or emacs to develop, other people prefer fully functional IDE's like visual studio, netbeans, eclipse, etc.As far as IDE's concerned, you should take a look at these options:-Netbeans.Decent IDE, feels kind of slow but gets the job done.-EclipseSimilar to netbeans.-AptanaA classmate uses this for PHP development. He likes it a lot.-Visual Studio with VS.PHPVS doesn't support PHP out of the box, but there are plugins so you can develop PHP within visual studio. Haven't tried it, but you should check this out if you like visual studio.Not IDE's, but great editros:-Notepad++Simple, fast and gets the job done.-VimHighly customizable, but hard to learn.-EmacsAlso highly customizable, and hard to learn.There's probably more out there, but these are the ones i know about. Just browse through them all and try the ones you think you will like.Once again, there's no best IDE or text editor. Just use the one that you like the most. If you're wondering what i like the most: Visual studio and notepad++ for anything not microsoft related. I'm too lazy to learn emacs or vim.References : Was this answer helpful?

--Vikas 05:07, 21 October 2013 (CEST)

Nikhil said ...

The problem with difineng your product based on Features is that it leaves you at the mercy of the various Eclipse projects and how they've chosen to define their Features. Not all of them do what I would consider a good job of it; some (many?) publish only one or a few very coarse-grained Features, rather than taking the time and effort to properly separate and distinguish multiple units of reuse. In the RCP apps I've worked on, bloat was a concern (justified or not) and using Features would have forced us to include and inherit a lot of stuff from Eclipse projects that we didn't really need or want.

--Nikhil 15:32, 21 October 2013 (CEST)

Manish said ...

I have a team implementing a apipicatlon on top of RCP right now, and I have to say we almost went with Netbeans rather then eclipse.The biggest problems with RCP are not it's name:1) No Visual Editor for apipicatlons means that every apipicatlon we right looks like Eclipse.2) The steep steep learning curve. The technology behind RCP is solid. Why is programming it so hard? Simple wizards to make actually functional EMF/Resource apipicatlons would be welcome.3) Speaking of which. EMF is so powerful. Why isn't there a forms/wizard based proccess to guide users through:* Create a EMF model.* Create a RCP apipicatlon that edits the EMF object.* Use TENEO extensions to make it write to and from database.* Make it easy to port this apipicatlon into RAP.The EMF + RCP stuff is so powerful that you could easily write a java apipicatlon that does CRUD. If we had the right tooling, it could be as easy as Ruby on Rails, but with a full desktop apipicatlon instead of a stripped down web apipicatlon.The points that Eclipse has going for it:1) EMF is wicked powerful. But where is the documentation to write a useful applciation? Why doesn't the mail app use a EMF model for example?2) OSGI.3) Existing OSGI functionality that can be added into other apipicatlons. Update site, etc. This needs to be easier.

--Manish 19:12, 21 October 2013 (CEST)

Maria said ...

I agree with you both as well. The org.eclipse.platform feature in pacariultr is not something I would add directly to a product. I usually add this feature to my target and then pull out the bundles I need into a custom feature.My argument here is really more about whether to use features at all or just stick with bundles. I can't imagine managing a non-trivial RCP app without features, but I'd be interested to hear from someone who has. Do either of you manage your product dependencies using bundles?

--Maria 04:21, 22 October 2013 (CEST)

Rodrigo said ...

I agree with you both as well. The org.eclipse.platform feature in parcatulir is not something I would add directly to a product. I usually add this feature to my target and then pull out the bundles I need into a custom feature.My argument here is really more about whether to use features at all or just stick with bundles. I can't imagine managing a non-trivial RCP app without features, but I'd be interested to hear from someone who has. Do either of you manage your product dependencies using bundles?

--Rodrigo 04:43, 22 October 2013 (CEST)

Arzo said ...

Features are a great feature, but I have to agree with Eric, the fartuees provided in the eclipse main P2 repository are not good citizens I've passed days trying to identify which fartuees would I use to setup a SDK IDE.There are lot of not described and lot of feature that has duplicated things.I ended up creating my own new Feature and adding the bundles that I wanted to.

--Arzo 06:00, 22 October 2013 (CEST)

Maria said ...

thanks for touching this pain point . In my own execnipree when talking with non Plug-in Developers, Eclipse is always perceived as an IDE and almost never as a Application Development Platform. I'm supportive of anything that would help change that.@Josh: I have looked at Eclipse Riena, and I like lots of it, but once again, how does this technology mix and match with everything else? Not well it seems.Josh, we are currently investigating how to allow Riena to mix and match better with existing RCP code-bases. One goal is to enable developers to use parts of Riena instead of forcing them to adopt all or nothing . Another goal is to refactor Riena so one can easily use GUI tools like SWT Designer with our code base.Regards,Elias.

--Maria 11:18, 23 October 2013 (CEST)

Vinicius said ...

I will listen to the poscadt, because I will never be able to listen to it live, 3:00 is prime time here, plus I have two home sick!! I am interested in this topic, for now, more as an adult child, but as my children get older I would love for them to feel empowered to have their own boundries (even as children when appropritate!) Thanks! Congratualtions, I'm sure it will be a wonderful success!Kathy recently posted..

--Vinicius 11:35, 23 October 2013 (CEST)

Sergey said ...

/ If I do anything in Linux for pmnigomrrag, I use Eclipse if I need an IDE. I also like doing as much as I can in terminal or even a note pad-like program. On Windows (for school), I really like using Notepad++, so the best alternative in Linux for NP++ that I've found is Geany.

--Sergey 14:15, 23 October 2013 (CEST)

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