jsonpatch_error() shutdown crash

[andysCaplin]

Hi. I'm getting a weird error trying to catch a jsonpatch_error(). My code is quite simple -

        try {
                    jsoncons::jsonpatch::apply_patch(jsonob->json, delta);
...
            } catch ( std::exception& e ) {
...

I'm assuming that std::exception is ok here - is that correct ?

This code works fine normally but sometimes I'm getting this crash during shutdown.

#0  0x0000003ae9a325e5 in raise () from /lib64/libc.so.6
#1  0x0000003ae9a33dc5 in abort () from /lib64/libc.so.6
#2  0x0000000000af6e75 in __gnu_cxx::__verbose_terminate_handler () at ../../../../libstdc++-v3/libsupc++/vterminate.cc:95
#3  0x0000000000af6a26 in __cxxabiv1::__terminate (handler=<optimized out>) at ../../../../libstdc++-v3/libsupc++/eh_terminate.cc:38
#4  0x0000000000af6a53 in std::terminate () at ../../../../libstdc++-v3/libsupc++/eh_terminate.cc:48
#5  0x0000000000af6bcf in __cxxabiv1::__cxa_pure_virtual () at ../../../../libstdc++-v3/libsupc++/pure.cc:50
#6  0x00000000006a4971 in message (this=<synthetic pointer>) at /usr/include/c++/4.8.5/system_error:158
#7  std::system_error::system_error (this=this@entry=0x7f7e78de5f80, __ec=...) at /usr/include/c++/4.8.5/system_error:316
#8  0x00000000006b431e in jsonpatch_error (ec=..., this=0x7f7e78de5f80, __in_chrg=<optimized out>, __vtt_parm=<optimized out>)
    at ../../libs/jsoncons/include/jsoncons_ext/jsonpatch/jsonpatch_error.hpp:19
#9  jsoncons::jsonpatch::apply_patch<jsoncons::basic_json<char, jsoncons::sorted_policy, std::allocator<char> > > (target=...,
    patch=...) at ../../libs/jsoncons/include/jsoncons_ext/jsonpatch/jsonpatch.hpp:487

i.e. It's saying a pure virtual method is being called when the patch errror message is being accessed.

Also, the patch message being processed is not invalid but is being interpreted as invalid.

This seems to happen only when we're shutting down the application.

I noticed that I can call the patch method and pass an errorcode ref and that won't throw an error so I could avoid the crash that way.

[danielaparker]

Catching a reference to a std::exception is fine.

Updating my earlier reply.

From the error message, it appears that you are using gcc 4.8.5. I think this error on termination is related to the fact that the std::error_category default constructor is not marked constexpr in libstdc++ in gcc 4.8, as it should have been, and which was fixed in 4.9. What this means is that we are not guaranteed that the initialization of our global object jsonpath_error_category_impl in

inline
const std::error_category& jsonpatch_error_category()
{
  static jsonpatch_error_category_impl instance;
  return instance;
}

is performed during constant initialization, which can lead to a static deinitialization issue, and which you would most likely observe when using shared libraries. I don't think you would see this error on termination with gcc 4.9 or later. If it's possible for you to check with 4.9, that would be much appreciated.

In any case, I'll implement a work around that should work with 4.8.

Daniel

[andysCaplin]

Thank your for replying so quickly.

All our build and development machines are on version 4.8.5 - but I'll try to get a machine with 4.9 and update here when I do that.

The issue we have is repeatable so I'll be able to verify any fix. I noticed that you created an error_category branch. I'll try testing that today.

In response to your earlier question the value of ec at frame 8 ( jsonpatch_error ) is

$1 = (const std::error_code &) @0x7fb96bffc8d0: {_M_value = 1,
  _M_cat = 0xfe6640 <jsoncons::jsonpatch::jsonpatch_error_category()::instance>}

One more question about this. Do you think that this issue could also have caused the messages to have been misdiagnosed as invalid in the 1st place ?
Because the other issue is that just before shutdown I get several logs indicating that I got invalid patch messages which aren't actually invalid. ( In the code extract above we log the exception message in the catch ).
In each of those cases the code has hit the catch successfully and the message has been extracted and logged.

[andysCaplin]

Ok - looks like I jumped the gun. I got this compile error using gcc 4.8.5 when I built the new branch you created.

../../libs/jsoncons/include/jsoncons_ext/jsonpatch/jsonpatch_error.hpp: In constructor ‘constexpr jsoncons::jsonpatch::jsonpatch_error_category_impl::jsonpatch_error_category_impl()’:
../../libs/jsoncons/include/jsoncons_ext/jsonpatch/jsonpatch_error.hpp:65:5: error: call to non-constexpr function ‘std::error_category::error_category()’
     {}


 60 class jsonpatch_error_category_impl
 61    : public std::error_category
 62 {
 63 public:
 64     constexpr jsonpatch_error_category_impl() noexcept
 65     {}

[danielaparker]

Too soon to try error_categry branch :-)

[andysCaplin]

Yeah -sorry. Got excited. Will try 4.9 if I can get a machine with it installed.

[danielaparker]

While comparing json_error.hpp and jsonpatch_error.hpp, which are otherwise similar, I noticed there was a difference in the order in which the error category class and exception class are defined. I changed jsonpatch_error.hpp to accord with json_error.hpp on master. Before proceeding further, could you download master and see if that changes anything?

Thanks,
Daniel

[andysCaplin]

Yes. I'll test today and get back as soon as I have a result. Thanks.

[andysCaplin]

Sorry, I just found out that we won't be able to test this til next week. As soon as we have tested it - I'll let you know the results. Thanks again for the quick response.

[andysCaplin]

Sorry but the crash still happens. I double checked the code to make sure that I had the latest changes. I printed the version string in the binary but it's 144 and that hasn't changed for a while.

I pulled the latest code today and noticed there are more changes but they don't seem related to the error message issue. I'll test with that as well though and add another note for those results.

Here's the stack trace info

#0  0x0000003ae9a325e5 in raise () from /lib64/libc.so.6
#1  0x0000003ae9a33dc5 in abort () from /lib64/libc.so.6
#2  0x0000000000b38f65 in __gnu_cxx::__verbose_terminate_handler () at ../../../../libstdc++-v3/libsupc++/vterminate.cc:95
#3  0x0000000000b38a76 in __cxxabiv1::__terminate (handler=<optimized out>) at ../../../../libstdc++-v3/libsupc++/eh_terminate.cc:38
#4  0x0000000000b38aa3 in std::terminate () at ../../../../libstdc++-v3/libsupc++/eh_terminate.cc:48
#5  0x0000000000b38cbf in __cxxabiv1::__cxa_pure_virtual () at ../../../../libstdc++-v3/libsupc++/pure.cc:50
#6  0x00000000006c3301 in message (this=<synthetic pointer>) at /usr/include/c++/4.8.5/system_error:158
#7  std::system_error::system_error (this=this@entry=0x7fb7be60a6a0, __ec=...) at /usr/include/c++/4.8.5/system_error:316
#8  0x00000000006e15fe in jsonpatch_error (ec=..., this=0x7fb7be60a6a0, __in_chrg=<optimized out>, __vtt_parm=<optimized out>)
    at ../../libs/jsoncons/include/jsoncons_ext/jsonpatch/jsonpatch_error.hpp:89
#9  jsoncons::jsonpatch::apply_patch<jsoncons::basic_json<char, jsoncons::sorted_policy, std::allocator<char> > > (target=...,
    patch=...) at ../../libs/jsoncons/include/jsoncons_ext/jsonpatch/jsonpatch.hpp:487

#8  0x00000000006e15fe in jsonpatch_error (ec=..., this=0x7fb7be60a6a0, __in_chrg=<optimized out>, __vtt_parm=<optimized out>)
    at ../../libs/jsoncons/include/jsoncons_ext/jsonpatch/jsonpatch_error.hpp:89
89                  : std::system_error(ec)
(gdb) p ec
$2 = (const std::error_code &) @0x7fb7d3ffc870: {_M_value = 1,
  _M_cat = 0xfe3210 <jsoncons::jsonpatch::jsonpatch_error_category()::instance>}

[andysCaplin]

Finally got a build on Red Hat 6 with a later tool chain containing GCC 8.3.1 and it fixes one of the 2 problems - i.e. the crash. This was with a binary with the original jsoncons i.e. without the fixes you implemented.

We still get deltas being misinterpreted as incorrect after shutdown but this is not an issue as we're shutting down anyway so we don't need to process these updates.