> 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..
