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From Oliver Deakin <oliver.dea...@googlemail.com>
Subject Re: [drlvm] Should the launcher print uncaught exceptions?
Date Thu, 21 Sep 2006 09:32:10 GMT
Hi Evgueni,

I wrote a simple launcher [1] that does the following:
1) Calls CreateJavaVM
2) Runs the main method of your Test class below
3) Calls DestroyJavaVM

Note that it does *not* call env->ExceptionDescribe() before destroying 
the VM.
I tested this launcher against the RI and J9 and found that no stack 
trace or
error details are printed.
So I would say that it is standard behaviour for the VM not to output any
information about uncaught exceptions when shutting down, and that the 
launcher
is expected to call ExceptionDescribe() if it wants any details to be 
printed.

So from what you have said below, IMHO we need to:
 - Change DRLVM to not print stack trace if there is an uncaught 
exception at
shutdown.
 - If necessary, change the launcher to make sure ExceptionDescribe() is 
called
before DestroyJavaVM().

Does that sound right?

Regards,
Oliver

[1]
#include <jni.h>
main() {
    JNIEnv *env;
    JavaVM *jvm;
    jint result;
    jclass cls;
    jmethodID mid;

    JavaVMInitArgs vmargs;
    vmargs.version = 0x00010002;
    vmargs.nOptions = 0;
    vmargs.ignoreUnrecognized = JNI_TRUE;

    result=JNI_CreateJavaVM(&jvm, (void**)&env, &vmargs);

    if (result<0) {
        fprintf(stderr, "Cannot create JavaVM\n");
        exit(1);
    }

    cls = (*env)->FindClass(env, "TestClass");

    if(cls == NULL)
    {
        printf("ERROR: FindClass failed.\n");
        goto destroy;
    }

    mid = (*env)->GetStaticMethodID(env, cls, "main", 
"([Ljava/lang/String;)V");
    if(mid==NULL)
    {
        printf("ERROR: GetStaticMethodID call failed.\n");
        goto destroy;
    }

    (*env)->CallStaticVoidMethod(env, cls, mid, NULL);

destroy:
    (*jvm)->DestroyJavaVM(jvm);
}



Evgueni Brevnov wrote:
> Hi All,
>
> I'm almost done with the implementation of Invocation API for DRLVM.
> While testing it I ran into a problem when an exception is printed
> twice. I created a simple application which just throws an error and
> it is not handled by any exception handler:
>
> public class Test {
>    public static void main(String [] args) {
>        throw new Error("my");
>    }
> }
>
> In this case the launcher calls env->ExceptionDescribe() before
> destroying VM.  Then it calls DestroyJavaVM() which identifies
> unhanded exception and calls an uncaught exception handler (see
> java.lang.Thread.getUncaughtExceptionHandler()) for the current
> thread. By default the handler prints the exception one more time.
> That's definitely differs from RI where the exception is printed out
> only once.
>
> To identify where the problem is I created another simple test and
> runs it on RI and DRLVM:
>
> public class Test {
>
>    static class MyHandler implements Thread.UncaughtExceptionHandler {
>        public void uncaughtException(Thread t, Throwable e) {
>            System.out.println("My Handler Called!!!");
>        }
>    }
>
>    public static void main(String [] args) {
>        Thread.currentThread().setUncaughtExceptionHandler(new 
> MyHandler());
>        throw new Error("my");
>    }
> }
>
> Here is the output:
>
> RI: java.exe Test
> My Handler Called!!!
>
> DRLVM: java.exe Test
> java/lang/Error : my
> at Test.main (Test.java: 12)
> My Handler Called!!!
>
> As you can see RI doesn't print exception stack trace at all. But
> DRLVM does. To be precise the launcher does. So we need to fix the
> launcher.....
>
> Note: The behaviour of DRLVM you have may differ from listed above
> since all experiments were done on my local workspace with Invocation
> API implemented.
>
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>

-- 
Oliver Deakin
IBM United Kingdom Limited


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