Legacy mode, module mode, mixed mode

[Alan Bateman]

Mandy - this is good informative write-up. A couple of comments inlined.


Mandy Chung wrote:
> :
>
> 0. Module Images
>
>   A module image consists of the jdk base module and a set of platform
>   modules.  The jdk modules are installed in the system module
>   library ($JAVA_HOME/lib/modules).
>
>   jre-module-image is the full JRE (equivalent the legacy j2re-image).
>   The "jdk.jre" module is the aggregator module representing the entire
>   JRE.
>
>   jdk-module-image is the full JDK (equivalent to the legacy 
> j2sdk-image).
>   The "jdk" module is the aggregator module representing the entire JDK.
>
>   rt.jar, tools.jar and other jar files no longer exist in the module
>   image.
Should this section include a few words to make it clear that the 
directory/file layout for the jdk-module-image is the same as the 
jre-module-image? Just thinking we should make it very obvious to the 
reader that the jdk image doesn't have the runtime in a "jre" directory 
as before.

>
> :
>
>   In the legacy mode, the system classes are loaded from the platform
>   modules installed in the system module library whereas non-system
>   classes are loaded from classpath, extension mechanism or custom
>   class loader as it is today.
Should this paragraph make it clear that the "non-platform" modules are 
ignored (and perhaps reference the migration/mixed-mode support in 
section C).

>
>
> :
>
> B) Legacy mode
>
>   There are various ways to alter the bootclasspath that will continue
>   to work in legacy mode:
>
>   1. -Xbootclasspath/p to prepend bootclasspath
>   2. Endorsed directory to prepend the default bootclasspath
>      via -Djava.endorsed.dirs (one or more directories) and
>      the default $JAVA_HOME/lib/endorsed directory
>   3. -Xbootclasspath/a to append bootclasspath
>   4. JVMTI and java.lang.instrument to append the bootclasspath
Should this section mention the extensions mechanism (ext directory 
where provider implementations and other JAR files are often copied into)?

> :
>
> A) Module mode
>
> 1. Current implementation
>
>   - The module boot path is passed by the java launcher as a
>     "sun.java.launcher.module.boot" system property and the
>     VM will find the primordial classes from that path.
Will this be a problem for custom launchers, folks using the JNI 
invocation API, etc?

-Alan.