Pls let it as it is!
-----Ursprüngliche Nachricht-----
Von: pjsip <pjsip-bounces@xxxxxxxxxxxxxxx> Im Auftrag von Ming
Gesendet: Mittwoch, 17. Oktober 2018 08:43
An: pjsip list <pjsip@xxxxxxxxxxxxxxx>
Betreff: Re: Patch for pjsua2
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-jav
>>> a/
>>>
>>> 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
>>> C++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.htm
>>> l#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
>>>
>>> _______________________________________________
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