Hi Christian,
There's quite a number of them actually. Counting from the Call class
only in Call.hpp, I find 12 methods that do not throw(Error) while 21
do, but the biggest difference is of course the constructor and
destructor. It will surely break a lot of applications and cause them
to fail to build. I tried it here and even our sample Java app
couldn't compile if all functions throw exceptions.
We appreciate your hard work, unfortunately Java and Android is a
major platform for PJSIP, and the exception specification is important
for this language/platform. In fact, due to the popularity of Android
alone, I will not be surprised if there are more users using PJSUA2
Java binding as compared to the native C++.
The PJ_THROW() is just an idea, it may not even have to be that way.
The necessary requirement is to make exception specifications and
runtime exceptions still work for languages and platforms that do
support them.
Best regards,
Ming
On Wed, Oct 17, 2018 at 2:15 PM, Christian Hoff <christian_hoff@xxxxxxx> wrote:
> Hello Ming,
>
> I see. Well, of course I can rework the patch to use this "PJ_THROW(..)" as
> you suggest - even though this would be quite frustrating because I spent so
> much time on eliminating the "throw" specification altogether, which is the
> much more complex option compared to a PJ_THROW() macro. So I would have to
> throw quite some code away. But I could still do it if you are convinced
> that this is the right way to go. Personally I am not really convinced
> because using "throw(..)" is deprecated in C++, so I think it might be
> better to get rid of this deprecated syntax altogether.
>
> But what I am wondering about is this: are there actually any C++ methods in
> PJSIP that currently do not have a "throw (Error)" in the throws
> specification? And how many are they? Is this actually a frequent case? From
> my experience it seems that almost all methods are declared as "throw
> (Error)". So the incompatibility might be minimal, but I am not sure.
>
> Best regards,
>
> Christian
>
>
>
> On 17/10/18 04:03, Ming wrote:
>>
>> Hi Christian,
>>
>> Unfortunately both options are still not ideal :)
>>
>> To make all generated Java methods to throw exceptions may require a
>> lot of changes in existing PJSIP Java apps, which is of course
>> undesirable.
>>
>> We still prefer the idea of replacing throw() with PJ_THROW(), which
>> will translate to no-op for C/C++ and throw() for SWIG. This way,
>> backward incompatibility is minimized while full feature is
>> maintained.
>>
>> Best regards,
>> Ming
>>
>> On Wed, Oct 17, 2018 at 4:46 AM, Christian Hoff <christian_hoff@xxxxxxx>
>> wrote:
>>>
>>> I am fordwarding this mail to the mailing list as well.
>>>
>>>
>>> On 16/10/18 22:42, Christian Hoff wrote:
>>>
>>> Hello Ming,
>>>
>>> you are absolutely right and I am sorry for the confusion. Of course the
>>> SWIG Java bindings throw "java.lang.Exception" and not the
>>> "RuntimeException" as I assumed.
>>>
>>> You actually discovered a bug in my patch. The problem with my patch is
>>> that
>>> I am throwing a java.lang.Exception from the Java JNI code, but this
>>> Exception is now no longer mentioned in the "throws" specification of the
>>> Java methods generated by SWIG - even though it is a checked exception.
>>> In
>>> fact my change (unintentionally) removed the "throw" specification also
>>> on
>>> the Java side! For this reason you no longer get compile errors when
>>> omitting the "catch" blocks in your sample code. This is a bug. Because
>>> the
>>> Exception is thrown from JNI C++ code, Java cannot find out that the
>>> generated C++ JNI code is actually violating the Java exception
>>> specification of the generated method (which declares that no checked
>>> exceptions should be thrown).
>>>
>>> After some reading of the SWIG documentation, I found out that there is a
>>> relatively simple way to fix this issue and to restore the "throw"
>>> specification on the Java side. To do this, please replace the line no.
>>> 50
>>> in file "pjsip-apps/src/swig/pj_error.i" by
>>>
>>> %javaexception("java.lang.Exception") {
>>>
>>> This should restore the "throw" specification for all PJSIP Java methods.
>>> I
>>> tested this briefly and it works. One possible downside of this change is
>>> however that this change will add a "throw Exception" specification to
>>> all
>>> generated Java methods inside PJSIP, so every PJSIP Java generated method
>>> now explicitly throws java.lang.Exception. This could be an issue if
>>> there
>>> are some PJSIP methods that cannot throw "pj::Error". In this case the
>>> user
>>> has to handle an exception that can never occur. However I am not even
>>> sure
>>> if such methods exist.
>>>
>>> Another option would be throw non-checked exceptions - such as
>>> RuntimeException - from the PJSIP Java bindings. But I think you like the
>>> idea of exception specifications and checked exceptions and therefore
>>> probably the first option will be the better one. As I said, the fix
>>> works
>>> by just changing a single line.
>>>
>>>
>>> Best regards,
>>>
>>> Christian
>>>
>>>
>>> On 16/10/18 11:24, Ming wrote:
>>>
>>> Hi Christian,
>>>
>>> Thanks for your detailed explanation, which I'm sure help us
>>> (especially me) improve our knowledge about Java.
>>>
>>> After checking the code (in pjsua2.i), our current exception actually
>>> uses java.lang.Exception, which, according to the reference below,
>>> belongs to checked exceptions. I verified this by trying to compile
>>> our sample code and remove a try-catch block and it did fail to
>>> compile.
>>>
>>> Ref:
>>> https://www.geeksforgeeks.org/checked-vs-unchecked-exceptions-in-java/
>>>
>>> Best regards,
>>> Ming
>>>
>>> On Tue, Oct 16, 2018 at 2:45 PM, Christian Hoff <christian_hoff@xxxxxxx>
>>> wrote:
>>>
>>> Hello Ming,
>>>
>>> thank you very much for your quick feedback and I am happy to hear that
>>> the
>>> propagation of exceptions works well with my patch!
>>>
>>> Regarding your point about exceptions and thr "throw (...)"
>>> specification:
>>> You are right in saying that an exception specification is still an
>>> important in programming languages such as Java. However in Java two
>>> kinds
>>> of exceptions exist and only one kind of them (the checked exception)
>>> works
>>> with exception specifications:
>>>
>>> Checked exceptions. Checked exceptions are the kind of exceptions that
>>> you
>>> are talking about, where the programmer is forced to somehow handle the
>>> exception. Handling the exception can mean either installing a catch
>>> handler
>>> or adding this exception type to the "throws" declaration of your method.
>>> If
>>> the exception is not handled, a compile error will be generated - as you
>>> wrote.
>>> Unchecked exceptions. Unchecked exceptions are the kind of exceptions
>>> that
>>> the programmer is not forced to handle. For this kind of exception, the
>>> programmer is not forced to install a "catch" handler, so no compile
>>> error
>>> will be generated if the exception is not handled at all. Such exceptions
>>> also do not appear in the "throws" declaration of the methods. Unchecked
>>> exceptions are all exceptions that derive from the RuntimeException and
>>> Error classes.
>>>
>>> For PJSIP a "pj::Error" was mapped to a RuntimeException up to now
>>> (already
>>> before my changes), so a "pj::Error" from the C++ PJSIP library raises an
>>> unchecked exception. This is true before and after my changes. This means
>>> that - as of now - a Java programmer is not forced to handle a
>>> "pj::Error"
>>> from the C++ code. This is because the "pj::Error" will be mapped to an
>>> unchecked exception. The consequence is that there is no compile error if
>>> the user forgets to install a catch handler on the Java side for errors
>>> from
>>> PJSIP. The exception for the "pj::Error" also does not appear in the
>>> "throws" declaration of the Java methods generated by SWIG as only
>>> checked
>>> exceptions should appear there, but not unchecked exceptions such as
>>> "RuntimeException".
>>>
>>> What I want to say in short is that my patch does not change anything in
>>> terms of exception handling on the Java side. The old behaviour was
>>> already
>>> to throw an unchecked exception that the user was not required to catch
>>> and
>>> the new approach is the same. And already before my changes we were not
>>> using exception specifications on the Java side as we were using
>>> unchecked
>>> exceptions. Or have I missed or overlooked something?
>>>
>>> What we might want to consider for the PJSIP Java bindings is to change
>>> the
>>> exception handling there to throw checked exceptions if a "pj::Error" is
>>> thrown from the C++ code, in order to force users to handle a
>>> "pj::Error".
>>> But this is more or less a separate change that does not really have
>>> anything to do with my changes.
>>>
>>> Thanks again for the quick testing and the quick feedback!
>>>
>>>
>>> Have a nice day and best regards,
>>>
>>> Christian
>>>
>>>
>>> On 16/10/18 06:31, Ming wrote:
>>>
>>> Hi Christian,
>>>
>>> I did some testing here and the exception does work great during runtime
>>> now!
>>>
>>> However, in my opinion, the "throw()" specification is still important
>>> for SWIG. While it's true that throw() is deprecated for C++, it
>>> remains a valid (and important) part of other languages such as Java.
>>> And having throw() in the declaration of the function will help the
>>> programmers during the development process.
>>>
>>> For example, if you try to call a function which throws an exception
>>> in Java but forget to put try and catch, the compiler will give an
>>> error such as:
>>> sample.java:155: error: unreported exception Exception; must be caught
>>> or declared to be thrown
>>>
>>> But it's now gone, so the developer must now carefully check each
>>> function in order to know whether it can throw an exception.
>>>
>>> Best regards,
>>> Ming
>>>
>>> On Mon, Oct 15, 2018 at 10:18 AM, Ming <ming@xxxxxxxxx> wrote:
>>>
>>> Hi Christian,
>>>
>>> Thank you for the hard work. Let us review and test this. Given the
>>> scale of the platforms and language binding affected, this may take
>>> some time. We will update you again.
>>>
>>> Best regards,
>>> Ming
>>>
>>>
>>> On Mon, Oct 15, 2018 at 4:19 AM, Christian Hoff <christian_hoff@xxxxxxx>
>>> wrote:
>>>
>>> Hello all,
>>>
>>> during the last weeks, I worked hard on the patch for PJSUA2 and C++ 17
>>> compatibility again. For those who have forgotten: Currently the PJSUA2
>>> headers cannot be compiled with C++ 17 because C++ 17 removes support for
>>> exception specifications. But unfortunately PJSUA2 makes have use of
>>> exception specifications.
>>>
>>> The open issue with my last patch was that SWIG no longer generates catch
>>> handlers that catch "pj::Error", as Ming pointed out. I have now updated
>>> the
>>> patch so that SWIG also generates the required catch handlers. Doing so
>>> has
>>> been a quite difficult, tedious and time-consuming task. But finally I am
>>> done and I am happy to share the resulting patch for inclusion into
>>> pjsip.
>>> The updated patch is attached to this mail.
>>>
>>> The magic on the SWIG side is done with the "%exception" directive, which
>>> installs a default global exception handler. In my updated patch, I am
>>> now
>>> using this "%exception" directive to generate the catch handler for
>>> "pj::Error" (see the new file "pjsip-apps/src/swig/pj_error.i"). The
>>> rationale behind this was that I really wanted to remove all the "throw
>>> (pj::Error)" from the header files, so I did not want to have a
>>> "PJ_THROW"
>>> that would expand to nothing during the compile and expand to the old
>>> "throw
>>> (...)" when using SWIG. "throw (...)" is now deprecated syntax and we
>>> should
>>> not keep it around for the sake of SWIG in my opinion.
>>>
>>> Some basic testing was also done:
>>>
>>> To verify the C++ 17 compatibility, I compiled my application with the
>>> installed adopted pjsua2 header files.
>>> To verify the generated SWIG language bindings and catch handlers:
>>>
>>> For the Python language binding, I verified that the compile works.
>>> Afterwards I installed the generated language binding and ran the test
>>> file
>>> "test.py". "test.py" also verifies the exception handling. I also
>>> inspected
>>> the generated catch handlers for pj::Error visually.
>>> For the Java and C# bindings, I verified that the compile works and
>>> inspected the generated catch handlers visually. Unfortunately I did not
>>> find a suitable unit test for the exception handling, but I am optimistic
>>> that it works nevertheless. I could not run the generated code for the C#
>>> bindings because I do not have Xamarin installed on my machine. But as I
>>> said, at least I can compile the C++ wrapper code for C#.
>>>
>>> I hope that this patch can now be considered for inclusion into PJSIP.
>>>
>>>
>>> Best regards,
>>>
>>> Christian
>>>
>>>
>>> On 25/09/18 10:26, Max Truxa wrote:
>>>
>>> Hello Christian,
>>>
>>> how about replacing the throw specifications with a macro that expands
>>> to nothing when compiling as C++ but `throw(Error)` when being parsed
>>> by SWIG?
>>>
>>> Something like this:
>>>
>>> #ifdef SWIG // defined if SWIG is parsing the file
>>> # define PJ_CAN_THROW throw(Error)
>>> #else
>>> # define PJ_CAN_THROW
>>> #endif
>>>
>>> struct Foo
>>> {
>>> void bar() PJ_CAN_THROW;
>>> };
>>>
>>> Regards,
>>>
>>> - Max
>>>
>>> On Tue, Sep 25, 2018 at 8:30 AM Christian Hoff <christian_hoff@xxxxxxx>
>>> wrote:
>>>
>>> Hello Ming,
>>>
>>> this is also an interesting idea. But will this actually work..? I am
>>> wondering because SWIG only parses the header files of PJSUA2. However
>>> the actual function implementation is in the ".cpp" source files and in
>>> these files you can find the code that throws the exceptions and that
>>> could use "PJ_THROW()". But to my knowledge SWIG does not parse the
>>> source files and would thus not know which functions may call
>>> "PJ_THROW". Or am I wrong about this?
>>>
>>>
>>> Best regards,
>>>
>>> Christian
>>>
>>>
>>> On 25/09/18 03:08, Ming wrote:
>>>
>>> Hi Christian,
>>>
>>> We haven't found a good way either. Our idea is to put PJ_THROW()
>>> macro to replace throw(), which can somehow be used by SWIG to
>>> generate the exception specs.
>>>
>>> Regards,
>>> Ming
>>> On Tue, Sep 25, 2018 at 4:21 AM Christian Hoff <christian_hoff@xxxxxxx>
>>> wrote:
>>>
>>> Hello Ming and all,
>>>
>>> I have now done some research into SWIG and exceptions. After reading
>>> the SWIG documentation, I found out that SWIG indeed parses the C++
>>> exception specification to figure out for what types of exceptions
>>> "catch(..)" should be generated (see
>>>
>>> http://www.swig.org/Doc3.0/SWIGDocumentation.html#SWIGPlus_exception_specifications
>>> ). Exception types that are specified in the exception specification are
>>> automatically propagated to the higher language (Java, C# etc.). Now
>>> that we need to remove the exception specification, we lose that
>>> capability. Thanks to Ming for the hint. However there is the
>>> possibility to adapt the SWIG interface file
>>> ("pjsip-apps/src/swig/pjsua2.i") and to add explicit "%catches"
>>> statements for each method that describe which types of exceptions the
>>> method could possibility throw. So I guess I need to rework my patch for
>>> this. I just hope that I will find some way to avoid having to annotate
>>> every method with "%catches".... I'll see. Or if someone knows how to do
>>> it, then I would be very grateful for a reply.
>>>
>>>
>>> Best regards,
>>>
>>> Christian
>>>
>>>
>>> On 24/09/18 12:43, Christian Hoff wrote:
>>>
>>> Hello Ming,
>>>
>>> thanks for your reply! I will have a look into the SWIG topic this
>>> evening and will let you know my findings.
>>>
>>>
>>> Best regards,
>>>
>>> Christian
>>>
>>>
>>> On 24/09/18 09:03, Ming wrote:
>>>
>>> Hi Christian,
>>>
>>> We apologize for the delay in response. We're currently reviewing it
>>> and have also managed to do some testing. While for C/C++, this seems
>>> to be okay, we're still considering how to best handle this for our
>>> Android and Java (via SWIG binding), which may still need the "throw"
>>> specifications in order for the developers to know that the functions
>>> may throw some exceptions.
>>>
>>> If you have any feedback regarding this, please let us know.
>>>
>>> Best regards,
>>> Ming
>>>
>>> On Mon, Sep 24, 2018 at 2:32 PM Christian Hoff
>>> <christian_hoff@xxxxxxx> wrote:
>>>
>>> Hello all,
>>>
>>> some feedback for this patch is still appreciated. In general I am
>>> getting somewhat frustrated about the collaboration with people who
>>> want
>>> to contribute to the project. Already in the past other people have
>>> posted patches here to this list, but did not get any response - not
>>> even a response what needs to be changed for the patch to be
>>> accepted. I
>>> think this is not a good mode of collaboration. Everyone who posts a
>>> patch here to this mailing list has done this with the intention to
>>> help
>>> the project PJSIP to move along (and has spent much time developing the
>>> patch), so you should at least return the favour and review the patch.
>>>
>>> This particular issue that I am trying to address with my patch (that
>>> the PJSUA2 headers don't compile against C++17) is an issue that you
>>> will eventually need to fix anyhow, so why not fix it right now? As of
>>> now, modern versions of GCC use C++ 14 by default, it is only a matter
>>> of time until C++ 17 will become the default and people will start
>>> complaining that there are compile errors from the PJSUA2 headers.
>>>
>>> Besides this, my own app uses PJSUA2 with C++ 17 features, so I would
>>> have to revert back to C++14 if this patch is not accepted upstream.
>>> This would be really unnecessary. So I would really appreciate a patch
>>> review.
>>>
>>> Best regards,
>>>
>>> Christian
>>>
>>>
>>> On 18/09/18 20:57, Christian Hoff wrote:
>>>
>>> Hello all,
>>> Hello Ming & Riza,
>>>
>>> do you have any feedback regarding this patch for C++ 17 support? I am
>>> also willing to rework it if required, but some feedback would be
>>> nice.
>>>
>>>
>>> Thanks in advance and kind regards,
>>>
>>> Christian
>>>
>>>
>>> On 12/09/18 18:23, Christian Hoff wrote:
>>>
>>> Hello all,
>>>
>>> currently it is not possible to compile a pjsua2 application with
>>> C++17. The reason is that C++17 removes support for dynamic exception
>>> specifications (that is "throws ..." declarations at the end of a
>>> function). Unfortunately PJSUA2 makes heavy use of exception
>>> specifications and most PJSUA2 functions are declared as "throw
>>> (Error)" - meaning that they can throw an exception of type "Error"
>>> that the programmer is supposed to catch.
>>>
>>> The consequence is that a lot of compile errors can be observed when
>>> compiling a pjsua2 application with C++17. The compile errors look as
>>> follows:
>>>
>>> /usr/local/include/pjsua2/json.hpp:80:33: error: ISO C++17 does not
>>> allow dynamic exception specifications
>>> virtual string saveString() throw(Error);
>>> ^~~~~
>>>
>>> The compile of the same application worked fine when using the C++14
>>> standard, but it got broken when I switched from C++14 to the C++17
>>> standard.
>>>
>>> See
>>>
>>> https://www.bfilipek.com/2017/05/cpp17-details-fixes-deprecation.html#removing-deprecated-exception-specifications-from-c17
>>>
>>> and
>>> http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2015/p0003r0.html
>>> for more background about the removal of exception specifications.
>>>
>>> To make the application compile again, I had to remove "throw(Error)"
>>> in the whole PJSUA2 source code and include files. This seems to be
>>> the only viable and good fix for this issue. I wrote my own "sed"
>>> script to do that and made some cosmetic corrections afterwards. Then
>>> I generated the attached patch file. Could you please apply this
>>> patch to the code base or give me feedback what I still need to
>>> improve? I verified that pjsip compiles fine with the patch applied.
>>>
>>> Thank you very much!
>>>
>>>
>>> Best regards,
>>>
>>> Christian
>>>
>>> _______________________________________________
>>> Visit our blog: http://blog.pjsip.org
>>>
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>>>
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>
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