i sort of agree with you. throwing an object through a DLL boundary may be
problematic due to memory allocation/deallocation. but in this case, it's
throwing a pointer (_jthrowable*), which is pretty much the same as
throwing an int...
On Tue, Nov 28, 2017 at 12:42 PM, Andi Vajda <va...@apache.org> wrote:
>
> > On Nov 28, 2017, at 11:27, William Schilp <william.sch...@ansys.com>
> wrote:
> >
> > i'm using JCC in a rather large project where a C++ interface drives a
> java
> > application through the JCC interface. the java application makes
> > considerable use of exceptions (as it should) and the C++ interface needs
> > to catch the various exceptions and perform various actions based on the
> > exception thrown. unfortunately i have to use visual studio to compile
> the
> > C++ interface as well as the JCC interface. with vs2012 i was getting
> > random problems when trying to extract information from an exception
> thrown
> > by the java application as ExceptionOccurred() would randomly return
> NULL..
> > with vs2015, ExceptionOccurred() always returns NULL. the basic flow was
> > this:
> >
> > // setup the JNI interface, which returns a pointer to the JNIenv
> > JNIEnv* jniEnv = setupJNIenv();
> >
> > _jthrowable* jException = NULL;
> > try
> > {
> > <call something via JCC which fails throwing an exception in the java
> > code>;
> > }
> > catch(_EXC_JAVA jErr);
> > {
> > _jthrowable* jException = jniEnv->ExceptionOccurred(); <--- in vs2012
> > this randomly returns NULL for exceptions that are caught
> > }
> > if(jException != NULL)
> > {
> > <do something for exception>
> >
> > as noted, ExceptionOccurred() would randomly return NULL when built with
> > vs2012, this was annoying but only happened on windows 10 machines. we've
> > moved to vs2015, and now ExceptionOccurred() always returns NULL. in
> > debugging this issue i put a break in JCCEnv::reportException():
> >
> > void JCCEnv::reportException() const
> > {
> > JNIEnv *vm_env = get_vm_env();
> > jthrowable throwable = vm_env->ExceptionOccurred(); <---- throwable is
> > not NULL here...
> >
> > if (throwable)
> > {
> > if (!env->handlers)
> > vm_env->ExceptionDescribe();
> >
> > // python code removed
> > }
> > throw _EXC_JAVA;
> > }
> >
> > when i break at vm_env->ExceptionOccurred() it returns a non-NULL
> > throwable. then when i break in my catch block: catch(_EXC_JAVA)...
> > and look at the return value for ExceptionOccurred() it returns NULL. for
> > whatever reason, between the break in reportException() at
> > ExceptionOccurred() and my catch block, whatever is supposed to store the
> > jthrowable pointer gets set to NULL.
> > so i made a change to the throw _EXC_JAVA to throw a copy of the
> jthrowable
> > as such:
> >
> > throw jthrowable;
> >
> > and then catch the jthrowable in my interface. this appears to work as
> the
> > jthrowable is now non-NULL and i'm able to extract the actual contents of
> > the exception.
> >
> > my questions:
> >
> > 1. Why does JCCEnv::reportException() throw an int instead of the
> > jthrowable?
>
> Because throwing object exceptions across DLL boundaries is fraught. Using
> int is recommended.
>
> > 2. do you have any idea why the return of JCCEnv::ExceptionOccurred()
> would
> > return non-NULL in reportException() and then in a later catch block
> return
> > NULL?
>
> If I remember correctly, the exception support requires JCC to be built in
> shared mode.
> Did you build it this way ?
>
> Andi..
>
>
>
