Andrey Chernyshev wrote:
With some changes I was able to run the DRLVM with classlib's
launcher. Here is what I did (you can see the experimental patch at
http://issues.apache.org/jira/browse/HARMONY-857):
- I have added JNI_CreateJavaVM declaration to jni.h (guess it will be
the most appropriate place for it);
- Added a simple implementations for JNI_CreateJavaVM and
DestroyJavaVM based on the existing create_vm and detroy_vm functions
in the vmcore/init submodule.
- To make vmcore/init functions visible for vmcore/jni code, I have
moved vmcore/init/init.h to vmcore/include;
- In parse_arguments.cpp, I had to silently ignore the option
"_org.apache.harmony.vmi.portlib" which is passed by the launcher to
VM for some reason, causing the DRLVM to complain about "unknown
option". What is the purpose of that option, should I process it
differently?
After all, I was able to run the DRLVM under classlib's launcher on
Windows with a command like:
Java.exe -vm:vmcore -vmdir:. Hello
and even was able to run Eclipse IDE with it. VM seems to exit cleanly
and didn't report any error messages.
Good work!
Some of the remaining issues / observations are:
(1)
DRLVM startup is organized a bit differently compared to the classlib
launcher startup, namely – the DRLVM after creating VM runs a special
class called VMStart which is, in it's turn, asynchronously calling
the main() method of the user application in a separate thread.
When we go with the classlib's launcher, the main() method is executed
in the same thread where the JavaVM is created.
What are the caveats with that?
I've had a look in the drlvm code, and I see what you mean - run_java_main
is expecting to receive the class name as a parameter, then launch the
VMStart class before running main().
It is standard practice for a Java launcher to call CreateJavaVM(),
then carry out a findClass() and CallStaticObjectMethod() on the specified
class and main method. However, the launcher does not necessarily have to
run the main method first - anyone could write a custom launcher that
calls a static "runme()" method first, or something similar, so the VM
should
not expect main() to be the first method called when launched from the
invocation API.
So, if I understand the drlvm code right, the call sequence on startup using
the drlvm launcher is:
drlvm launcher calls vm_main()
vm_main() calls create_vm() (which is essentially CreateJavaVM)
create_vm() completes and returns
vm_main() calls run_main()
run_main() calls run_java_main()
run_java_main() creates the VMStart class and executes its start() method
run_java_main() creates the specified class and runs its main() method
When drlvm is launched using a generic launcher (such as the classlib
launcher) the sequence would probably need to be either:
launcher calls CreateJavaVM()
CreateJavaVM() passes call to create_vm()
create_vm() makes its usual calls, but also executes required VMStart
code
create_vm() and CreateJavaVM() both exit, returning control to the
launcher
or:
launcher calls CreateJavaVM()
CreateJavaVM() passes call to create_vm()
create_vm() makes its usual calls and returns. A flag is set to
indicate that VMStart still needs to be run.
create_vm() and CreateJavaVM() both exit, returning control to the
launcher
launcher makes a call to run some Java code (possibly main method)
drlvm picks up flag indicating VMStart needs to be executed and runs
it before the specified class
The first approach seems better to me, since it gets all of the vm
initialization
completed within the CreateJavaVM() call.
Does this answer your question? Any other ideas?
(2)
If I pass a wrong app class name to the classlib launcher, drlvm
reports class not found exception and then is crashed. This happens
because the classlib launcher, once it fails to run the app class,
reports an exception (with ExceptionDescribe) but doesn't clear it
(doesn't call ExceptionClear). Then it immediately goes with
DestroyJavaVM those current implementation in drlvm doesn't expect
that there is some pending exception object in the TLS.
Eventually, destroy_vm fails with assert in the class loading code
while resolving VMStart class (VMStart holds the Java part of the
shutdown method), because it mistakenly picks up the ClassNotFound
exception object. It is remaining from unsuccessful attempt of
classlib launcher to run the app's class main method.
The question is, who's responsibility should be to clear the exception
object in that case? I tend to think that classlib launcher should be
doing this once it takes the responsibility to process the possible
exceptions while running the app main class.
Although the classlib launcher should probably tidy up after itself and
call ExceptionClear, I don't believe that there is a spec requirement to
clear pending exceptions before calling DestroyJavaVM. Therefore
any launcher could call DestroyJavaVM with an exception pending,
and drlvm would throw a ClassNotFound.
IMHO drlvm should handle the fact that an exception already exists
on entering DestroyJavaVM, and clear it before trying to resolve
the VMStart class.
(3)
CreateJavaVM can only be called once for now – many internal data
structures in DRLVM are kept as global variables (jni_env, java_vm,
Global_Env e.t.c.). Therefore, it will be hard to organize the
multiple instances of JavaVM unless all these things are encapsulated
somewhere (into JNIEnv?).
(4)
Launcher wants the vm dll in the "default" directory unless the option
is specified. Should we realign the drlvm build output and move all
dll's into the "default" subdir?
yup, or put it into a deploy/jdk/jre/bin/drlvm directory and use the
launcher
options to specify its location.
(5)
What to do with the "_org.apache.harmony.vmi.portlib" option that
launcher is offering to VM?
This passes the classlib port library function table to the VM. I think
this just makes the classlib port library available to the VM for it to
use/query if it wishes. I think it is fine for the drlvm to ignore this
option
if it wants to.
Regards,
Oliver
Most likely there are more issues that I'm overlooking at the moment.
Please consider the suggested patch is a workaround to make the things
working, I'm wondering if there is a more graceful way to do this.
Thanks,
Andrey.
On 7/11/06, Andrey Chernyshev <[EMAIL PROTECTED]> wrote:
OK, so I'm going to add CreateJavaVM into vm\vmcore\src\jni\jni.cpp
and also add implementation into DestroyVM (stub is already seem to be
present there) based on destroy_vm(). Then we'll see how it works with
the launcher.
Thanks,
Andrey.
On 7/11/06, Geir Magnusson Jr <[EMAIL PROTECTED]> wrote:
> This has been my thinking - even if not perfect, lets get it working
> using the launcher and then fix as required. It's arguable if that
> "brokenness" matters at this point, and I think that there's plenty to
> be gained from having it work via the launcher.
>
> geir
>
> Rana Dasgupta wrote:
> > create_vm() looks quite close/complete to being a complete
prototype for
> > CreateJavaVM,
> > but I think more work is needed in DestroyVM which prototypes
DestroyJavaVM
> > for functional completeness. It is non waiting on user threads,
it does not
> > send the corresponding JVMTI shutdown events, I also don't know
if it
> > handles shutdown hooks cleanly ( but these "may" not be critical
right now
> > for hooking up to the launcher ). What do you think?
> >
> > When I ran a non trivial test.. upto 32 threads instantiating a
very large
> > number of objects with -XcleanupOnExit which uses
DestroyVM, it
> > exited cleanly. Maybe OK to hookup and fix bugs as we go.
> >
> > Thanks,
> > Rana
> >
> >
> > On 7/10/06, Andrey Chernyshev <[EMAIL PROTECTED]> wrote:
> >
> >> >Yes, it seems like the launcher will need at least
JNI_CreateJavaVM
> >> >and DestroyJavaVM functions.
> >>
> >> >I couldn't find implementation for CreateJavaVM in drlvm codebase.
> >> >Perhaps create_vm() function in vm\vmcore\src\init\vm_main.cpp
can be
> >> >adopted for that purpose?
> >> >Is there are any tricks and caveats one should be aware of before
> >> >trying to produce CreateJavaVM from it?
> >>
> >> >I've also seen a prototype for DestroyJavaVM in
> >> >vm\vmcore\src\init\vm.cpp - comment says it needs to be
improved to
> >> >wait till all Java threads are completed.
> >>
> >> >Any more ideas what needs to be done to implement those?
> >>
> >> >Thanks,
> >> >Andrey.
> >>
> >>
> >>
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--
Andrey Chernyshev
Intel Middleware Products Division
--
Oliver Deakin
IBM United Kingdom Limited
