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Hi,

I'm trying to throw an exception from my native C++ code, the code
snippet looks like this:

/////////
jclass clsException = pEnv->FindClass("MyExceptionClass");
if(clsException )
{
pEnv->ThrowNew(clsException, "HelloWorld");
}
return;
/////////

The 'ThrowNew' method is called, but no exception seems to be thrown or
caught on the Java side.

ThrowNew returns 0 if it's any help, and if I call 'ExceptionCheck'
afterwards, it returns 'true', before that it returns 'false' meaning
that the exception pending is the one that I have just thrown.

Any ideas would be appreciated,

Thanks,

Yaron

On 6 Sep 2005 09:59:07 -0700, wrote:
> I'm trying to throw an exception from my native C++ code, the code
> snippet looks like this:
>
> /////////
> jclass clsException = pEnv->FindClass("MyExceptionClass");
> if(clsException )
> {
> pEnv->ThrowNew(clsException, "HelloWorld");
> }
> return;
> /////////
>
> The 'ThrowNew' method is called, but no exception seems to be thrown
> or caught on the Java side.
>
> ThrowNew returns 0 if it's any help, and if I call 'ExceptionCheck'
> afterwards, it returns 'true', before that it returns 'false'
> meaning that the exception pending is the one that I have just
> thrown.

There's nothing wrong with the code you've posted, but there might be
something wrong in the code you didn't post.

For example, what is "ExceptionCheck()"? Do you mean
ExceptionOccurred()?

Have you tried calling ExceptionDescribe() after ThrowNew() to see
whether it really is your exception that's been thrown?

How are you handling this in the caller?

/gordon

--
[ do not email me copies of your followups ]
g o r d o n + n e w s @ b a l d e r 1 3 . s e

On 6 Sep 2005 09:59:07 -0700, wrote or quoted :

>jclass clsException = pEnv->FindClass("MyExceptionClass");
>if(clsException )
>{
> pEnv->ThrowNew(clsException, "HelloWorld");
>}
>return;

Is there a debugger that lets you debug Java when in Java and C++ or
MASM when in C++?
--
Canadian Mind Products, Roedy Green.
http://mindprod.com Again taking new Java programming contracts.

On Tue, 06 Sep 2005 09:59:07 -0700, yarona wrote:

>
> Any ideas would be appreciated,

I think your problem might be that after a ThrowNew, the native method
does not abruptly terminate automatically. That is, flow of control
returns to your native method, and the new exception is pending at this
point. You need to "abort" your method manually if ExceptionOccurred()
returns true (or handle the exception in native code, which is something
i'd call "severe pain").

--
You can't run away forever,
But there's nothing wrong with getting a good head start.
--- Jim Steinman, "Rock and Roll Dreams Come Through"

On 6 Sep 2005 09:59:07 -0700, wrote or quoted :

> pEnv->ThrowNew(clsException, "HelloWorld");

Insert this after the Throw:

pEnv->DeleteLocalRef( clsException );

Your problem basically is that C++ knows nothing about Java
exceptions. Exceptions are just control blocks lying about. It is up
to you in some C++ish way, after you set up the exception, return
quickly and gracefully up the call stack to your caller back in Java
who can then handle the exception. On your way back, C++ can handle or
notice the exception by explicitly testing for it with ExceptionCheck.

In Abundance this is known as a "graceful bailout".


--
Canadian Mind Products, Roedy Green.
http://mindprod.com Again taking new Java programming contracts.

On 6 Sep 2005 09:59:07 -0700, wrote or quoted :

> pEnv->ThrowNew(clsException, "HelloWorld");

see http://mindprod.com/jgloss/jni.html#EXCEPTIONS

also check out the book link that will explain this all for you.
--
Canadian Mind Products, Roedy Green.
http://mindprod.com Again taking new Java programming contracts.

On Tue, 06 Sep 2005 23:01:58 GMT, Roedy Green wrote:
> On 6 Sep 2005 09:59:07 -0700, wrote or quoted :
>
>> pEnv->ThrowNew(clsException, "HelloWorld");
>
> Insert this after the Throw:
>
> pEnv->DeleteLocalRef( clsException );

No, don't. There is seldom any need for DeleteLocalRef(), and
certainly not in this case.

This is akin to telling him to null method local references before
returning from a Java method.

/gordon

--
[ do not email me copies of your followups ]
g o r d o n + n e w s @ b a l d e r 1 3 . s e

Hello all, and many thanks for your replies,

"ExceptionCheck()" is a method which is much like "ExceptionOccured"
only it returns jboolean rather than a jthrowable.

I am returning from the native method immidiatly after "ThrowNew" (
actually I'm calling "ExceptionDescribe" first, and it is my exception
that is thrown).
I also put a break point in the exception object's c'tor on the Java
side, and sure enough it's getting called, meaning that it's being
created.

The Java side looks something like this:

try
{
MyThrower thrower = new MyThrower();
thrower.ExceptionThrowingMethod(); // a native method
}
catch(MyExceptionClass e)
{
//handle exception
}

MyExceptionClass is derived from java.lang.Exception

But I never reach the catch clause - even though as I've mentioned, the
"MyExceptionClass" object was constructed.

Thanks,

Yaron

On 7 Sep 2005 01:34:10 -0700, wrote:
> "ExceptionCheck()" is a method which is much like "ExceptionOccured"
> only it returns jboolean rather than a jthrowable.

Hmm, I wasn't even aware that that method existed, but I see it now in
the docs...

> I am returning from the native method immidiatly after "ThrowNew" (
> actually I'm calling "ExceptionDescribe" first, and it is my exception
> that is thrown).

This could very well be the problem: In my experience,
ExceptionDescribe() seems to clear the exception, at least sometimes.

Apparently others have also seen this behaviour:
http://bugs.sun.com/bugdatabase/view...bug_id=4067541

Try removing these checks from your native code. Just throw the
exception, then return.

/gordon

--
[ do not email me copies of your followups ]
g o r d o n + n e w s @ b a l d e r 1 3 . s e

On 7 Sep 2005 08:45:03 +0200, Gordon Beaton wrote:
> On Tue, 06 Sep 2005 23:01:58 GMT, Roedy Green wrote:
>> On 6 Sep 2005 09:59:07 -0700, wrote or quoted :
>>
>>> pEnv->ThrowNew(clsException, "HelloWorld");
>>
>> Insert this after the Throw:
>>
>> pEnv->DeleteLocalRef( clsException );
>
> No, don't. There is seldom any need for DeleteLocalRef(), and
> certainly not in this case.

Additionally, the JNI docs state clearly which JNI functions are safe
to call when there is a pending exception (as is the case here), and
DeleteLocalRef() isn't among them:

http://java.sun.com/j2se/1.5.0/docs/...n.html#wp17626

/gordon

--
[ do not email me copies of your followups ]
g o r d o n + n e w s @ b a l d e r 1 3 . s e