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