Difference between pages "Java Configuration Design Update" and "User:Bunyk"

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This page describes a potential update to the Java support code in Gentoo and Funtoo Linux, with the intention of simplifying <tt>java-config</tt> code and also making it more correct and better integrated with Portage itself. The proposal intends to address deficiencies in the current design of <tt>java-utils-2.eclass</tt> while maintaining its useful features and avoiding a full rewrite. Rather than replace the current system with more code, the goal is to simplify the existing code while retaining functionality, while allowing a graceful migration of advanced functionality inside Portage itself.
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== Design Challenges ==
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The current Java eclasses have some very interesting and powerful features, yet are lacking in some areas.
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=== Dependency Handling ===
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Currently, <tt>java-utils-2.eclass</tt> uses <tt>depend-java-query</tt> to automatically select the most optimal Java VM for building. This is a sophisticated feature that is intended to be 'smart', yet it has some flaws. These flaws are fixable:
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* While JVM auto-selection is smart, it is not always correct -- it doesn't use Portage's API, but instead uses regexes to parse the currently-executing ebuild's <tt>DEPEND</tt> string.
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* Related to the regex issue, the code in <tt>depend-java-query</tt> is complex as it tries to duplicate some functionality that could be handled better by Portage's API.
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This proposal provides a mechanism for the Portage API to be used to always generate a completely correct result. This may seem like a minimal optimization since the existing code is correct ''most'' of the time. But it is duplicative, in that it does a rough approximation of what the Portage API could do absolutely correctly. So there is no good reason to keep it -- less code means more maintainability.
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{{fancyimportant|Moreover, there is even a better reason for doing things the right way -- eclasses should as much as possible be able to behave as "first-class citizens" in the world of Portage. This is an important architectural goal, and there are severe costs for not pursuing it, namely having every eclass under the sun re-implement various parts of Portage, albeit poorly, creating much uncessary code and frustration!}}
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=== Atoms ===
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Currently, <tt>eselect java-vm</tt> and <tt>java-config</tt> have their own "atoms" that they use to identify Java virtual machines, which seems to be <tt>${PN}-${SLOT}</tt>. Yet Portage already has atoms, and we should try to allow support for them over time. This proposal does require there to be some "link" between the existing JVM atom and the Portage atom. This link currently does not exist.
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== Proposal ==
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=== java-config Settings ===
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This proposal involves a minor upgrade to the java-config settings for a JVM -- adding a <tt>PORTAGE_ATOM</tt> setting to the file, which allows the <tt>java-config</tt> atom to be linked to the Portage atom:
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{{file|name=/usr/share/java-config-2/vm/oracle-jdk-bin-1.7|desc=Java-config settings|lang=bash|body=
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# Copyright 1999-2011 Gentoo Foundation
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# Distributed under the terms of the GNU General Public License v2
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# $Header: /var/cvsroot/gentoo-x86/dev-java/oracle-jdk-bin/files/oracle-jdk-bin-1.7.env,v 1.2 2011/11/17 22:49:56 caster Exp $
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VERSION="Oracle JDK 1.7.0.60"
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JAVA_HOME="/opt/oracle-jdk-bin-1.7.0.60"
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JDK_HOME="/opt/oracle-jdk-bin-1.7.0.60"
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JAVAC=${JAVA_HOME}/bin/javac
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PATH="${JAVA_HOME}/bin:${JAVA_HOME}/jre/bin"
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ROOTPATH="${JAVA_HOME}/bin:${JAVA_HOME}/jre/bin"
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LDPATH="${JAVA_HOME}/jre/lib/amd64/:${JAVA_HOME}/jre/lib/amd64/xawt/:${JAVA_HOME}/jre/lib/amd64/server/"
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MANPATH="/opt/oracle-jdk-bin-1.7.0.60/man"
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PROVIDES_TYPE="JDK JRE"
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PROVIDES_VERSION="1.7"
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BOOTCLASSPATH="${JAVA_HOME}/jre/lib/resources.jar:${JAVA_HOME}/jre/lib/rt.jar:${JAVA_HOME}/jre/lib/sunrsasign.jar:${JAVA_HOME}/jre/lib/jsse.jar:${JAVA_HOME}/jre/lib/jce.jar:${JAVA_HOME}/jre/lib/charsets.jar:${JAVA_HOME}/jre/classes"
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GENERATION="2"
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ENV_VARS="JAVA_HOME JDK_HOME JAVAC PATH ROOTPATH LDPATH MANPATH"
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VMHANDLE="oracle-jdk-bin-1.7"
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BUILD_ONLY="FALSE"
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PORTAGE_ATOM="dev-java/oracle-jdk-bin-1.7.0.60"
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}}
 
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With this very minor and easy-to-implement change, new possibilities are available -- namely, for <tt>java-config</tt> code to tap into the Portage API and leverage its advanced dependency handling functionality.
 
 
<div style="float: right; width: 40%; margin-left: 1em; margin-top: 1em; margin-bottom: 1em; background-color: #f8f8f8; padding: 0.5em; border-radius: 8px;">
 
 
=== Provides ===
 
 
{{fancynote|This section is not a requirement for the implementation of this proposal, but a suggestion for future Portage development.}}
 
 
Currently, the functionality that is provided by each JVM is stored in the <tt>java-config</tt> file shown above, namely in the <tt>PROVIDES_TYPE</tt> and <tt>PROVIDES_VERSION</tt> variables. This works for us, though it is unfortunate that the (in my opinion) not completely thought-out [http://wiki.gentoo.org/wiki/GLEP:37 GLEP 37] was implemented, which deprecated the <tt>PROVIDES</tt> variable in Portage. This is a useful variable because it gave us a "link" from the installed package to the virtual it provided. No such link currently exists, which is a reduction in useful functionality.
 
 
It is recommended that <tt>PROVIDES</tt> is un-deprecated in Portage, and used by ebuilds solely for recording what virtuals are provided by the ebuild, so that they can be queried later once the package is installed. This would allow <tt>PROVIDES_TYPE</tt> and <tt>PROVIDES_VERSION</tt> -- functionality duplicated by the Java tools -- to be removed, further reducing the complexity of the Java tools codebase.
 
</div>
 
 
=== java-config Dependency Handling ===
 
 
With these changes, <tt>java-config</tt> and <tt>depend-java-query</tt> to tap directly into the power of Portage dependency handling. Let's see how.
 
 
=== Query: List installed VMs ===
 
 
To list installed VMs, <tt>java-config</tt> could look in <tt>/usr/share/java-config-2/vm/</tt> to get a list of all installed Java VMs. However, thanks to the <tt>PORTAGE_ATOM</tt> variable, it can then compile a list of corresponding package atoms in <tt>/var/db/pkg</tt>.
 
 
=== Query: Is a Suitable or Best VM Selected? ===
 
 
Currently, the <tt>java-utils-2.eclass</tt> attempts to magically select the proper VM for building based on the contents of the <tt>DEPEND</tt> string. This is how this functionality would be implemented correctly, using the Portage API rather than custom code.
 
 
To perform this query correctly and efficiently, <tt>depend-java-query</tt> can compile a list of Portage atoms for all installed Java VMs, along with what virtual they provide using <tt>PORTAGE_ATOM</tt>, <tt>PROVIDES_TYPE</tt> and <tt>PROVIDES_VERSION</tt>. Then, the <tt>DEPEND</tt> handed to it can be correctly evaluated using Portage functions. This is how the Portage side of the algorithm would work:
 
 
# Pre-process <tt>DEPEND</tt> string:
 
## Remove all components that are not related to <tt>virtual/jdk</tt> and <tt>virtual/jre</tt>.
 
## Evaluate <tt>DEPEND</tt> string using currently-active USE settings to remove all conditionals.
 
# Create a <tt>fakedbapi</tt> and <tt>cpv_inject()</tt> the current system VM Portage atom into it.
 
# Evaluate the pre-processed <tt>DEPEND</tt> string and see if the dependencies are satisfied.
 
# If so, a suitable VM is selected.
 
 
To find the "best match" VM, a similar process would be followed. Instead of <tt>cpv_inject</tt>ing the current system VM, ''all'' installed VMs would be injected and a best match would be found.
 
 
== Future Directions ==
 
 
=== Reusing Code, Merging into Portage ===
 
 
Since this functionality could use useful to other eclasses, this could be used as a test for a more generic helper function that could be integrated into Portage. This would allow other eclasses to implement similar functionality without having to have their own custom helper applications.
 
 
The <tt>java-config</tt> settings file could be merged into <tt>/var/db/pkg</tt> and a simple API could be added to <tt>vartree</tt> and <tt>dblink</tt> to provide API access to it. This would provide a toolkit for eclasses for storing extra configuration settings with installed ebuilds, which could be useful for a variety of purposes.
 
 
All these goals support the idea of code re-use and maintainability, and addressing the problem at the correct architectural level.
 
 
[[Category:Portage]]
 
[[Category:FLOP]]
 
[[Category:Java]]
 
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Latest revision as of 10:10, July 2, 2014

Taras Bunyk

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Lviw, Ukraine (49.839683, 24.029717000000005The type of this property is invalid)