On Tue, Apr 16, 2013 at 10:43 PM, ecat <emaman...@gmail.com> wrote:

> I've been using C++ GPBs in a real-time robotics system and have been
> getting (VERY rarely) a segfault when I use a protobuf copy constructor.
> When I say very rarely, I mean once in hundreds of thousands of method
> calls. I've followed the gdb backtrace multiple times, and it's always THIS:
>
> #0  0xad252ac5 in construct (this=0x8a00b20, __position=..., __x=...) at
> /usr/include/c++/4.6/ext/new_allocator.h:108
> #1  std::vector<google::protobuf::UnknownField,
> std::allocator<google::protobuf::UnknownField> >::_M_insert_aux (
>     this=0x8a00b20, __position=..., __x=...) at
> /usr/include/c++/4.6/bits/vector.tcc:335
> #2  0xad25233c in push_back (this=0x8a07608, field=...) at
> /usr/include/c++/4.6/bits/stl_vector.h:834
> #3  push_back (this=0x8a07608, field=...)
>     at
> /path/to/protobuf/protobufsrc/src/google/protobuf/unknown_field_set.cc:140
> #4  google::protobuf::UnknownFieldSet::AddField (this=0x8a07608, field=...)
>     at
> /path/to/protobuf/protobufsrc/src/google/protobuf/unknown_field_set.cc:142
> #5  0xad2523ac in google::protobuf::UnknownFieldSet::MergeFrom
> (this=0x8a07608, other=...)
>     at
> /path/to/protobuf/protobufsrc/src/google/protobuf/unknown_field_set.cc:64
> #6  0xad0eaacc in messages::MyProtobuf::MergeFrom(messages::MyProtobuf
> const&) ()
>    from /path/to/our/library
> #7  0xad0eb180 in messages::MyProtobuf::MyProtobuf(messages::MyProtobuf
> const&) ()
>    from /path/to/our/library
>
> The code it traces back to is:
>         std::map<float, ClassWithGPBMember> cdf;
>
>         float prev = 0.0f;
>         for(iter = particles.begin(); iter != particles.end(); ++iter)
>         {
>             ClassWithGPBMember c = (*iter);
>
>             // For loop continues
>         }
> Where ClassWithGPBMember has a member of type MyProtobuf (not a pointer).
> The copy in #7 above must come from the assignment in the first line of the
> for loop.
>
> I have looked at UnknownFieldSet, and if I understand correctly, it holds
> unrecognized fields from when a message is parsed. My messages (at least at
> this stage of the code) have not been serialized or parsed; we create them
> and set the fields. There is no way for us to have added an unknown one. So
> my question is, how could I have interfered with the UnknownFieldSet
> without having done any parsing? Also, any ideas on why is would occur so
> rarely? I would typically guess a timing bug, but all processing of this
> message is within one thread.
>
Do you share the map<float, ClassWithGPBMember> across multiple threads? Or
maybe the program is running out of memory when doing the copy?


>
> Anybody seen this before or know what could cause this? It's a bit beyond
> my understanding of GPBs.
>
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