This document is under construction.
Generally speaking, an OSGi framework (hereafter we call fw) needs some configuration files for its launch. A fw will be launched by invoking java command or by executing an executable launcher file. In the former case, configurations for fw implementation to to read will be required. In the latter case, executable launcher file also might read some configuration files at its invocation.
- As in Eclipse, org.eclipse.osgi plug-in that contains main class of equinox fw implementation reads config.ini in a configuration area. In addition, eclipse.exe is provided as an executable launcher which reads eclipse.ini in the same directory and invokes fw.
Currently, the focus of OSGi Service Platform Specification has been to standardize a runtime infrastracture. On the other hand, how to configure and launch a fw is not addressed. Therefore, scenarios such as bootstrapping OSGi on a clean system are left difficult to manage in a fw independent way.
Overview:What FramerowkHandler enables?
We would like to address this problem by proposing a simple API that would allow to configure a non running framework and launch it in a fw independent way. Framework Handler provides fw independent way for a bundle running on a fw to do the followings.
- Set configurations required to launch a fw, such as
- Java VM location,
- Java VM arguments,
- executable launcher location,
- beginning start level and initial bundle start level,
- Bundles to be installed and started with their start levels,
- fw configuration location,
- fw persistent date location,
- Launch a fw with the specified configurations, such as Java VM, Java VM arguments and so on.
- Expect its bundles state if the specified configurations are used for a fw launch.
Terminologies used in here
- Fw config files
- configuration files that will be read by a fw implementation at its launching, e.g. config.ini in the directory specified by osgi.configuration.area system property as for equinox.
- Executable launcher
- an executable fw launcher file, e.g. eclipse.exe as for Eclipse.
- Launcher config files
- configuration files that will be read by an executable launcher, e.g. eclipse.ini as for eclipse.exe.
- Bundles state
- state of bundles that represents what kinds of bundles are installed, resolved and to be started on a fw.
Senarios that the API would help
- PDE UI
- to ease the targetting of various frameworks
- Provisioning agent
- to setup a non running framework
- Building an application
- to create all the config files required to run
- Running the framework
- to configure and start a framework from java command
API: Package org.eclipse.core.fwhandler
Interfaces defined in org.eclipse.core.fwhandler package will be introduced briefly. See the codes and Java docs in detail.
The only interface whose implementation will be registered into the OSGi service registry in this package is FwHandlerAdmin.
The client bundle will get the appropriate FwHandlerAdmin service object that can meet its requirements by filtering service properties in the service registry. An example of filtering is the target fw implementation and its version. As for filtering, later section will explain it in detail. Then, the client will get new instance of FwHandler which plays a main role in this API.
In addition, it also has a method to launch a fw according to the specified FwHandler object.
A client bundle can get a FwHandler object by FwHandlerAdmin.getFwHandler(). This object keeps both a FwConfigData object and a FwLauncherData object, each of which has setter and getter methods on parameters to be required for a fw launch. The client can set some parameters to be required for launching a fw via FwConfigData object or FwLauncherData object. The parameters set in this object can be saved. Where to save is determined according to the parameters set at that time in a target framework and launcher implementation dependent way.
The client also can load parameters from fw config files and launcher config files in the specified locations.
After parameters are set to this object either by setting via a FwConfigData or a FwLaucnherData or loading from configuration files, FwHandlerAdmin.launch(FwHandler, File) will launch a fw according to the current parameters set in this object. It migiht invoke a fw by java command or executing the specified launcher.
Remember if you have set parameters but not have saved yet, this launch might use other parameters because actual launch will use parameters retrieved from the configuration files.
In addition, FwHandler enables for a client bundle to expect bundles state if the specified configurations are used for launch without actual launch.
FwConfigData is a class that keeps some parameters for a FwHandler object such as,
- Bundles list to be installed, with their persistently marked flag as started or not and their start level for its configuration.
- Beginning start level and initial bundle start level.
- System properties dependent of a fw implementaion.
- System properties independent of a fw implementaion.
For most fw implementaions, these parameters will be saved into their fw config files. However, this API doesn't restrict where to save. For example, a fw implementation and a launcher implementation might need to save these parameters not in fw config files but in a launcher config files. It depends on the target implementations.
FwLauncherData is a class that keeps some parameters for a FwHandler object such as,
- Location of Java VM.
- Java VM arguments.
- Location of fw config files.
- Location of fw persistent data, where a fw implementation save information to be kept persistently, such as bundles state, permissions of bundles, start level information, private persistent storages for bundles, and so on. In addition, this location sho
- Clean flag: a flag to clean the specified locaiton of fw persistent data.
For most fw implementaions, these parameters will be saved into their launcher config files, if executable launcher is used. However, this API doesn't restrict where to save. As in Apache Felix, location of fw persistent data should be written in its fw config file. Therefore, the implementation of FwHandler for Felix should save it into not launcher config file but its fw config file.
The implementating object of FwBundleState will be created by FwHandler object. At the time of its creation, this object will compose bundles state according to the parameters that the FwHandler object keeps. It means, bundles which can be obtained by FwHandler.getFwConfigData().getBundles() will be installed on a virtually launched fw using parameters about fw persistent data location. If the data location is not empty and clean flag is false, the installed bundles persistently recorded there should be taken into consideration to compose the bundles state.
After creating this object, this object also provides ways for a client to resolve bundles, install additional bundles, uninstall bundles virtually. Modification of this object never affects the parameters of the FwHandler object which created this object.
Provider of these APIs
First of all, we supposed that an implementation of this API for each fw implementation will be provided by the implementators of the target fw, because the persons who know the fw implementaion the most are the implementators of the target fw.
For clients to filter the proper service object, the provider must register the FwHandlerAdmin object with service properties keyed by the followings.
- String; name of the framework
- String; version of the framework
- String; name of the launcher
- String; version of the launcher
- Current Limitation: there is no version range.Version Range might be required.
Offline, the implemenentator of FwHandlerAdmin must declare these values and client must know them.
Client of these APIs
A client bundle will get appropriate FwHandlerAdmin service object from an OSGi service registry by filtering the service properties described previously in order to get the FwHandler objects to handle the desired fw and launcher implementation.
Which interface should a method of launch operation belong to?
Currently, a method of launch operation belongs to FwHandlerAdmin interface. I can seperate this API into another interface like "FwLauncher". But I am not sure how much merit of it would be.
- One merit of the separation is, we can restrict some bundles so that can configure a fw but cannot launch it, by not giving ServicePermission("GET","FwLauncher").
- One demerit of it is, number of interface will be increased by one, even if this interface only has one method.
Launching a fw instance in the Same Process
At this point, launching a fw instance in the same process is not considered yet in this API, explicitly. However, it will be supported in the future.
- What is not sure is “general way of launching a fw instance in the same process”. The API might be able to support it (JavaVM and JavaVM arguments are not used for it obviously).
How to get the running fw information?
There is a need for manipulating configurations not only non-running fw but also running fw. The following stuff are not determined yet. But that's our current idea for realizing it.
Realizing the following goals will result in realizing what we want.
- allow a client to know the values required for filtering in order to get the proper FwHandler service object that can manipulate the running fw.
- allow a client to know FwConfigLocation, FwPersistentDataLocation, and FwLauncherLocation of a running fw.
- This location contains the fw config files that used for a target fw launch.
- This location contains the fw persistent data files that used for a target fw launch.
- This location contains the fw launcher file that used for a target fw launch.
Then, a client can get information about running fw and manipulate it after setting the location information to the FwHandler object.
First, let me think about how we realize the first goal. In order to know the values about running fw, coorporation of fw and launcher implementation is required. We would like to standardize as follows:
- A fw implementation will receive values about its launcher name, version, and location of its executable launcher, somehow, if executable launcher is used. The way how to pass the values from a launcher to a fw implementation is not specified here. The typical way is via system properties keyed by the predefined name. On the other hand, a fw implementation itself can specify its fw implementation name and version.
- Then, a fw implementation needs to tell these information to a client somehow. There are several ways to realize it.
- One of them is assigning the dedicated key name of framework properties that can be retrieved by BundleContext#getProperty(name). For example of the dedicated key name are "org.osgi.framework.service.fwhandler.fwname/fwversion/lanchername/launcherversion".
- The other is defining another service interface that is registered by a fw implementation and allows a client to get these information.
Next, let me think about how we realize the second goal. While we defined it yet, there are two ideas how to realize it:
- A fw implementation will register several DataLocation services for each Location of running fw, as an API of org.eclipse.osgi.service.datalocation.Location.
- A fw implementation will register a DataLocation service, whose methods allow a client bundle to get to know each location of running fw. In this case, this API also can provide the information about fw name/version and launcher name/version as described previously.