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https://issues.apache.org/jira/browse/HBASE-3260?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12965845#action_12965845
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Neil Bartlett commented on HBASE-3260:
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I was directed to this JIRA by a Twitter conversation between Gary and
@asynchronaut (Holger Hofstätte)
If you are looking for a lightweight library that can help to provide OSGi-like
lifecycle management, there is an obvious answer: OSGi itself. Apache Felix is
a fully certified OSGi implementation and it is just a 300k JAR file. It can be
embedded in a Java application with literally five lines of code.
You seem to be concerned that OSGi is heavyweight. While it's true that it is
used in many heavyweight servers including e.g. IBM WebSphere, the core of OSGi
is very tight indeed, consisting of only 15 interfaces and 16 classes (of which
9 are "Permission" classes for Java 2 security).
By embedding OSGi you will benefit from existing tools and skills, in addition
to opening up the possibility for users to use many higher level frameworks
that build on top of OSGi. Also you will be using lifecycle management code
that is very well tested and proven.
> Coprocessors: Lifecycle management
> ----------------------------------
>
> Key: HBASE-3260
> URL: https://issues.apache.org/jira/browse/HBASE-3260
> Project: HBase
> Issue Type: Sub-task
> Reporter: Andrew Purtell
> Fix For: 0.92.0
>
> Attachments: statechart.png
>
>
> Considering extending CPs to the master, we have no equivalent to
> pre/postOpen and pre/postClose as on the regionserver. We also should
> consider how to resolve dependencies and initialization ordering if loading
> coprocessors that depend on others.
> OSGi (http://en.wikipedia.org/wiki/OSGi) has a lifecycle API and is familiar
> to many Java programmers, so we propose to borrow its terminology and state
> machine.
> A lifecycle layer manages coprocessors as they are dynamically installed,
> started, stopped, updated and uninstalled. Coprocessors rely on the framework
> for dependency resolution and class loading. In turn, the framework calls up
> to lifecycle management methods in the coprocessor as needed.
> A coprocessor transitions between the below states over its lifetime:
> ||State||Description||
> |UNINSTALLED|The coprocessor implementation is not installed. This is the
> default implicit state.|
> |INSTALLED|The coprocessor implementation has been successfully installed|
> |STARTING|A coprocessor instance is being started.|
> |ACTIVE|The coprocessor instance has been successfully activated and is
> running.|
> |STOPPING|A coprocessor instance is being stopped.|
> See attached state diagram. Transitions to STOPPING will only happen as the
> region is being closed. If a coprocessor throws an unhandled exception, this
> will cause the RegionServer to close the region, stopping all coprocessor
> instances on it.
> Transitions from INSTALLED->STARTING and ACTIVE->STOPPING would go through
> upcall methods into the coprocessor via the CoprocessorLifecycle interface:
> {code:java}
> public interface CoprocessorLifecycle {
> void start(CoprocessorEnvironment env) throws IOException;
> void stop(CoprocessorEnvironment env) throws IOException;
> }
> {code}
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