Please review: VM side of Jigsaw classpath mode support

[Mandy Chung]

On 8/23/2012 1:14 PM, Karen Kinnear wrote:
> The VM side of this webrev is at:
>      http://cr.openjdk.java.net/~acorn/vm.classpath/webrev/
Looks good, Karen.  I should take this opportunity to describe
the new properties VM sets for JDK to use but they are removed
from System properties at startup time

sun.boot.class.prepend.path - paths set by -Xbootclasspath/p
sun.boot.class.append.path - paths set by -Xbootclasspath/a and
   added by JVMTI or java.lang.instrument.
   The above 2 are used for searching system resources.
   It used to search system resources from "sun.boot.class.path"
   but in a modular JDK, we need to separate the prepend and
   append paths.  We take this simple approach to pass these 2
   properties to the JDK properties since the VM already has
   the separated search paths.

sun.boot.module.classpath - Class.getPackage() calls JVM_GetSystemPackage
   to obtain the source where a system class is loaded (it may
   be a JAR file or a directory).  If a system class is loaded
   from a module image in classpath mode, it can be loaded from
   any module for the runtime.  The current VM implementation
   only supports an entry to the bootclasspath be appended.
   In addition, there is no manifest for modules anyway. All
   we need is to tell the JDK that this system class is loaded
   from modules; then it will construct a Package instance
   based on the system properties.  So sun.boot.module.classpath
   serves as a unique tag for JDK to compare with the returned
   value from JVM_GetSystemPackage.

I have a few minor comments and you can be addressed in
future revisions.  There will be another update for modulepath
support next.

In os.cpp, does it need to reset UseModuleNativeLibs if there
is no base module?  You already check for the flag and
has_module_image():
   if (UseModuleNativeLibs&&  Arguments::has_module_image())

os.cpp L1140-1142 - I thought this is no longer needed and can be
removed.

classLoader.hpp looks like "_boot_module_source" is not used.
BTW, should Arguments::boot_module_index() belong to classLoader.hpp?

It's an open issue what "sun.boot.class.path" should be.
I believe your current patch includes the legacy rt.jar and other
paths in sun.boot.class.path because you want the VM to be able
to run on a legacy image (e.g. JDK8).  Perhaps you can detect from
JDK_Version if it's a jigsaw build, not to include the legacy paths
in sun.boot.class.path.  I have been considering adding some interface
to indicate it's a modular image (since the JDK release is still 8
in our build).  I can add a bit in the jdk_version_info in our next
revision.

Thanks
Mandy