Robert Ramey
Martin Lederhilger wrote:
Hello Robert, hello Bogdan,
I have quite the same problem (Exception multiple_code_instantiation
thrown in basic_serializer_map.cpp at line 48) as Bogdan. It can be
reproduced by changing
the pointer type from polymorphic_base to polymorphic_derived2 in the
original test_dll_exported.cpp example, which comes with the library.
I think the problem is that when oa << BOOST_SERIALIZATION_NVP(rb2);
is called, that the system registers an type in oserializer.hpp, which
leads to creation of the singletons also in the executeable.
Ahhhh - a very useful hint. So the rule would be that if a class
is polymorphic is to be serialized through a pointer, it should ONLY
be done through a base class pointer? That is, if ALL polymorphic
base classes are abstract - this problem will never occur?
I'll have to think about this.
I have this problem when serializing a shared_ptr<A> in class B in
B.dll to an object of class A in A.dll.
I tried to simply comment out this check, but it seems that I get
problems with tracking later. I have a class hierarchy like this:
C derives from B derives from A. A has a weak_ptr<A> to itself
(something like boost::enable_shared_from_this). If I serialize an
object of type C via a base pointer of type B the serialization walks
like this: C::serialize, B::serialize, A::serialize, and again
C::serialize (with a wrong this pointer - and it should not do that).
Hmmm - why should it not do that? You may have a cycle - but
the library handles that. Seems unrelated to the other problem.
Maybe my second problem depends on the first one. I hope that my
report can be of help.
Thanks in advance for your answers,
And thanks for your useful information.
Martin Lederhilger
Hello Robert,
On your suggestion I have run a few tests. I hope they help:
I commented out the registration macro associated to the base class in
ExportDll.dll:
- //BOOST_CLASS_EXPORT_IMPLEMENT(polymorphic_base)
To make the example more realistic I modified the inheritance hierarchy as
follows:
class polymorphic_base{};
class polymorphic_derived1 : public polymorphic_base{};
class polymorphic_derived2 : public polymorphic_derived1{};
I added one integer data member to polymorphic_derived1 and
polymorphic_derived2.
Here are the results:
==================================================
Polymorphic serialization through a pointer to polymorphic_base WORKS AS
EXPECTED:
// Save code -----------------------------
polymorphic_base *rb0 = new polymorphic_derived1(100);
polymorphic_base *rb1 = new polymorphic_derived1(10);
polymorphic_base *rb2 = new polymorphic_derived2(10,20);
oa << BOOST_SERIALIZATION_NVP(rb0);
oa << BOOST_SERIALIZATION_NVP(rb1);
oa << BOOST_SERIALIZATION_NVP(rb2);
// Load code -----------------------------
polymorphic_base *rb0 = NULL;
polymorphic_base *rb1 = NULL;
polymorphic_base *rb2 = NULL;
ia >> BOOST_SERIALIZATION_NVP(rb0);
ia >> BOOST_SERIALIZATION_NVP(rb1);
ia >> BOOST_SERIALIZATION_NVP(rb2);
The serialized content is presented below:
- for polymorphic_xml_[io]archive
<?xml version="1.0" encoding="UTF-8" standalone="yes" ?>
<!DOCTYPE boost_serialization>