Re: [Swig-devel] Exception handling in C#

[William S F. <ws...@fu...>]

On 22/10/13 15:16, Marvin Greenberg wrote:
> I'm looking at migrating the director exception handling from Java over
> to C#.  I actually think there is more work than a simple port -- the C#
> capabilities are missing some of the preexisting (before my patch)
> capabilities in Java.  Specifically, the equivalent of a "throws"
> typemap in java to map thrown exceptions from C++ into an "equivalent"
> exception in C#.
The throws typemap should work in C#. What isn't working? Perhaps you 
are referring to the 'throws' attribute in all the Java typemaps? These 
are very Java specific for checked exceptions and not relevant to C# though.

But, for now I have a simple question as I'm trying to
> understand the process of carrying exceptions from the C++ layer into C#.
>
> In the code below, is numExceptionsPending serving any purpose?  It
> seems like only a single exception can be pending.  Is this some
> performance issue -- assignments are expensive so don't want to hold the
> lock?  It seems like simply testing pendingException for null is
> sufficient.
It is a performance optimisation where performance is most critical when 
there are no exceptions pending and hence a non-thread local variable is 
read in the normal code path which is a lot faster than reading a thread 
local variable.

There is the possibility of more than one exception pending if more than 
one thread is in use. The csharp_exceptions_runme.cs file tests this.


With regard to the Java exceptions patch, I think there are a handful 
more things to be done, that is:

- Derive DirectorException from std::exception in all languages for 
consistency as well as add in support for directorthrows in the other 
director languages for a consistent experience for directors and exceptions.

- Add support for $packagepath/$javaclassname in the Java "throws" 
typemap using a call to canonicalizeJNIDescriptor()

- Your patches to directorout typemaps and std_string.i add in an
   if (!jenv->ExceptionCheck())
call. This needs to be done in all Java directorout typemaps that throw 
exceptions and also in the documentation (and examples/test-suite)

- Have you looked at the two warnings in the Java test-suite, they look 
related to director exceptions:
WARNING in native method: JNI call made with exception pending
	at director_abstract.director_abstractJNI.Foo_ping(Native Method)
	at director_abstract.Foo.ping(Foo.java:54)
	at director_abstract_runme.main(director_abstract_runme.java:29)


WARNING in native method: JNI call made with exception pending
	at 
director_exception.director_exceptionJNI.Foo_pongSwigExplicitFoo__SWIG_1(Native 
Method)
	at director_exception.Foo.pong(Foo.java:62)
	at director_exception_runme.main(director_exception_runme.java:21)


William