Transcript A Peek at the Next Releases of SMF and OSGi

IBM Pervasive Computing
A Peek at the Next Release:
OSGi
BJ Hargrave and Peter Kriens
[email protected] [email protected]
OSGi Fellows
OSGi Confidential | 08 Aug 2003
© 2003 IBM Corporation
IBM Pervasive Computing
General Requirements
 Backward compatible
 Transparent
 Life cycle aware
 Optional
 Focus on embedded systems
 Flexibility
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Service & Resource Arbitration
 Problem
– Multiple clients need to use the same service but the service can not
be (partly) shared
 Use case
– Telephone used in normal operation when an emergency call need to
be made. How is the current user of the telephone notified?
– The audio system is used by he nav system when a phone call comes.
The nav system must give up the audio system until the call is finished.
 Requirements
– Session Management: Grant deny, terminate, suspend, resumed, abort
– As transparent as possible
– Notifications about resource usage changes
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Resource Management
 Problem
– A system must carefully manage its resource usage (memory, cpu
cycles, threads, etc.) by bundles to guarantee the correct operation of
the service platform.
 Use case
– A bundle is to be installed. The bundle is interrogated for its persistent
storage requirements. This are compared with the available storage.
There is sufficient storage and the bundle is installed.
 Requirements
– Ability to describe and check resource requirements of a bundle
– Notification of exceeding resource allocation
– Monitoring of allocated resources
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Power State Notification
 Problem
– Bundles need to be able to react to imminent power state changes to:
• Maintain integrity
• Conserve energy.
 Use case
– The navigation system has a display and a CD-ROM drive. When the
car goes to battery mode, the CD-ROM and display need to be
powered down. When the engine is started, the CD-ROM and display
can be powered up.
 Requirements
– Allows monitoring of power states in (near) real time
 Note: May be realized by the creation of a general event delivery
mechanism with specific power state events.
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Diagnostics Support
 Problem
– Need a generalized mechanism to perform diagnostics on services and
devices connected to the service platform
 Use case
– Navigation system is sometimes displaying incorrect map data. The car
is taken in for service and the technician has a diagnostic bundle
installed. The diagnostic bundle performs tests on all the connected
devices and determines the GPS has a memory error.
 Requirements
– Request self test of device
– Monitor/collect device data
– Change device parameters
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CECED & EHS
 Problem
– EHS is a highly popular power line bus in Europe for home automation
and CECED is an abstraction of busses like EHS. Whitegood devices
connected to such buses need to be supported in the OSGi
environment.
 Use case
– User buys a washing machine and connects it up in home. The OSGi
gateway discovers this device on the powerline network and installs a
bundle for the device. The bundle collects information from the washing
machine and sends it to the manufacturer. The manufacturer, can now
perform remote diagnostics if necessary.
 Requirements
– Provide low level API to support communication between bundle and
device
 Note: Need to agree on CECED vs. EHS as abstraction
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Web Container
 Problem
– The OSGi SP as an application server has several advantages over a
J2EE environment. J2EE web applications should therefore run on
OSGi SP without much effort.
– Low level web site development with the servlet API requires skilled
(expensive) programmers. Content developed for OSGi based
platforms should be able to leverage existing web development tools
 Use case
– A developer uses WSAD to create a web application using servlets and
JSPs. This application can be test using WSAD. The resulting WAR file
is preprocessed by a tool that converts it to a bundle. This bundle is
installed and the web application can then be accessed.
 Requirement
– Use of standard web application development tools
– Pre-compilation of JSPs
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Bundle Suite
 Problem
– Sometimes bundles are not standalone but work with other bundles to
form an application
 Use case
– An application developer creates an application which is composed of
several bundles. These bundles share packages and services and are
closely coupled. An application assembler wants to assemble the
complete application (all necessary bundles) in one deliverable. It
therefore needs a standard artifact to hold the bundles and their
associated metadata.
 Requirement
– Define a flexible, extensible file format for delivery
– Support localization
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Transient Bundles
 Problem
– OSGi bundles are always permanently installed. Sometimes this is not
desirable since a bundle may only be necessary for a very short time.
After this it should be removed reliably.
 Use case
– A bundle containing a GPS firmware update is installed in the OSGi
device of a car. The bundle is started and updates the firmware on the
GPS. After this, the bundle is no longer needed and can be uninstalled.
 Requirement
– Allow framework to avoid persistent storage of transient bundles
– Automatically remove transient bundle when framework
stopped/restarted for reliability reasons
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Allow Bundles To Change Their State
 Problem
– A certain class of bundles can determine when they can be stopped or
uninstalled. However, the OSGi framework forbids these bundles to
stop/update/uninstall themselves because the calls are synchronous.
 Use case
– A technician must diagnose a car and loads a bundle in the platform. IT
performs the diagnosis and after this diagnosis is performed, the
bundle is no longer necessary.
 Requirement
– Provide an asynchronous mechanism for bundle to request to be
uninstalled, updated or stopped.
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Enumeration of Resources Within a Bundle
 Problem
– Resources contained in a bundle cannot be discovered in runtime,
requiring that the application to have a-priori knowledge of the content.
Many patterns exist where applications can adapt to included content
dynamically. These patterns can currently not be used.
 Use case
– A web container bundle implementing the Servlet (2.3) API needs to
implement the ServletContext.getResourcePaths method. This method
allows a web application to examine its contained resources.
 Requirement
– Provide a method that can be called to enumerate the resources in a
bundle.
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Code Matching Enhancements
 Problem
– The native code is only selected by OS, processor and language. In
certain cases, this set is not sufficient to make the correct decision. A
richer selection algorithm is necessary.
– There are sometimes platform dependencies on pure Java code
requiring alternative implementations. There is currently no means to
selectively load these implementations.
 Use case
– Eclipse GUI (SWT) requires native code and a Java library. For Unix, it
can run on Motif and X requiring a specific native code library and
swt.jar for each. Bundles can carry the alternatives and right shared
library and jar file is selected in run time.
 Requirement
– A general and extensible mechanism to select components in the
Bundle-NativeCode and Bundle-Classpath header
– Reuse existing selection techniques.
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Optional Native Libraries
 Problem
– Some Native libraries may not be required for all platforms because
there is a fallback mechanism when the native library does not exist.
Currently if a native library is specified, a library must exist for the
specific platform or the installation will completely fail.
 Use case
– A bundle provides a crypto API to other bundles. This bundle contains
an all Java implementation of the crypto API so that it operates on all
platforms. The bundle also contains native implementations of the
crypto library for some platform as a performance enhancement.
 Requirement
– Installation of a bundle must (optionally) succeed if a native library is
not available
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Life Cycle Transactions
 Problem
– Certain bundle installations can be dependent upon each other. In
those cases it is necessary to install all or none of the bundles.
 Use case
– A feature (made up of one or more bundles) is to be installed via the
Eclipse update manager. The update manager creates a bundle life
cycle transaction object. It then performs bundle installations, updates
and uninstalls against the transaction. If all the operations are
performed without an exception, the update manager commits the
transaction.
 Requirement
– Bundle life cycle operations can be grouped and validated for success
before being committed
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Singletons

Problem
– There are times when it is appropriate that only a single version of a
bundle, service or a package is present in the framework

Use case
– A bundle provides the UI framework for the device. There is only one
display on the device and correspondingly there should only be one
bundle providing the UI framework. The bundle is marked a singleton
so the framework can prevent attempts to install or use another
version of the bundle.

Requirement
– Detect and prevent multiple versions being present at the same time
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Bundle as Module

Problem
– Bundles need to share classes based upon implementation versions.
Current class sharing is based upon package exporting by
specification version. Many time the packages to be shared are not
well specified and really contain implementation details. It may also be
the case that these packages should not be globally exported to all
bundles.

Use case
– The xerces parser consists of many packages which contain the
implementation of the parser. The developer specifies that his bundle
is dependent on the xerces bundle as a module using some versioning
constraints (e.g. = 4.1.*). When the developer’s bundle is resolved, its
class loader will then have access to all the implementation packages
in the xerces bundle.

Requirement
– Allow bundles to share classes based upon the implementation
versions of the bundles
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Bundle Fragments

Problem
– Sometimes bundles can be composed of parts which do not always
have to be deployed at the same time but are still strongly coupled

Use case
– A bundle developer seperates the national language message catalogs
from the base bundle into a set of bundle fragments, one per national
language. The base bundle and some set of the corresponding
fragments are installed. The message catalogs in all the installed
fragments are now loadable by the base bundle.

Requirement
– Provide a way for a bundle to be logically extended (within same
classloader) by separately installed components
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Export Multiple Versions of a Package
 Problem
– In large systems, installed applications can depend upon different
versions of the same package
 Use case
– Bundle A depends upon version 2.1 of the servlet API. Another
application in bundle B is dependent upon version 2.3 of the servlet
API. Neither bundle can work with the other version of the API. Both
bundles can be run and are bound to the proper version of the API.
 Requirement
– Multiple versions of the same package can be exported
– Bundles can bind to specific versions of an exported package
– Bundles bound to different versions of a package cannot exchange
object or detect services between each other to avoid
ClassCastException
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Different Package Specification Major Versions are defined
to be Non Compatible
 Problem
– Sustain backwards compatibility over major specification version
changes is not always feasible for larger systems.
 Use case
– The specification for a package is updated to a new major version. The
update introduces a non-backwards compatible change because a
method is removed. A bundle which imports the package at an earlier
major version is not exposed to the new major version of the package.
 Requirement
– Interpret specification version numbers according to a
major.minor.micro scheme with major version changes being noncompatible
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Filter packages from Base ClassLoader
 Problem
– The base java platform may include packages which cannot be
updated by a bundle
 Use case
– The J2SE installation provides a version of Xerces and the
org.w3c.dom and org.xml.sax packages. These packages are an older
version that the one needed by bundles running in the framework. So
we want to install a bundle which exports a newer version of these
packages. The framework must be configured to “hide” the old version
of these packages from all bundles, so that the new versions of the
packages can be instead used.
 Requirement
– Allow specific package provided by the base classloader to be
overridden by bundles
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Version Overrides
 Problem
– Version constraints expressed by bundle developer may cause the
installed bundle set to be unresolvable. Though in reality these bundles
could operate correctly with the provided versions.
 Use case
– Bundle A is written and specified to require bundle B version 1.2 or
higher. When installing the bundle, the management agent is informed
by the management system that bundle A has been tested successfully
and will work with bundle B version 1.1 which is already installed. So
that management agent overrides the required version information and
the framework will resolve bundle A using bundle B version 1.1.
 Requirement
– Allow management agent to override version constraints
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Demand Loading of Services from Bundles
 Problem
– Registering a service from a bundle requires the bundle to have a
classloader, be started and explicitly register a service. This requires
significant resources before the service is ever used.
 Use case
– A bundle containing an XML parser implementation wishes to register
SaxParserFactory and DocumentBuilder services to allow other
bundles to use the parser. The bundle declaratively specified these
services. The framework will automatically load and start the bundle
when someone requests the service.
 Requirement
– Allow bundle to declare services to be registered
– Start bundles on demand when services are obtained
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Dynamic Extensions to the Service Registry
 Problem
– In many cases services may be provided by external service registry
where it is not feasible to preregister all the external services in the
local OSGi service registry because of performance
 Use case
– A bundle attempts to find a service. The service is a web service which
is found in a UDDI registry. A bundle which communicates with the
UDDI registry will intercept the find request and can then provide
services matching the web service.
 Requirement
– Allow the service find mechanism to be extended to bundles
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Finer grained Framework administration permissions

Problem
– AdminPermission is too coarse grained. It protects too many different
privileged operations.

Use case
– HttpService currently requires AdminPermission to call
Bundle.getResource to access resources in a bundle. This requires
HttpService to be fully trusted and makes it difficult to use 3rd party
providers for this simple service.

Requirements
– Finer grain replacement for AdminPermission
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Bundle Signing
 Problem
– Currently the integrity and authenticity of bundles must be determined
in a proprietary way. This prevents interoperation and tooling support.
 Use case
– A bundle is installed in the framework. The framework validates the
integrity and authenticity of the bundle and completes the install. When
the bundle is loaded from the local storage, the framework again
validates the integrity and authenticity of the bundle. The permissions
for the code in the bundle is assigned based upon the code signers.
 Requirements
– Allow for standard mechanism to validate the integrity and authenticity
of the bundles
– Allow permissions for bundles to be assigned based upon the signers
of the code
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