Re: Marshalling auto_ptr/unique_ptr objects
On 7 Mrz., 09:29, Brian <c...@mailvault.com> wrote:
I'm adding support for auto_ptr/unique_ptr to the C++
Middleware Writer. In the past I've gotten a few pointers
on implementations here and since I'm not an expert on
either of those classes, I would like to get some
feedback on what I have so far. There are two pieces
of input:
Disclaimer: I don't know the C++ Middleware Writer
and given the context of this newsgroup you
might get further replies that concentrate on the
C++ language aspects of your question. Many
type definitions remain unresolved in your
posting and I didn't look into the details
that your link will probably provide.
class mytype
{
[..]
void
Send(SendCompressedBuffer* buf, bool = false) const
{
SendMemberData(buf);
}
What is the meaning of the bool parameter, that is
not used: Forward compatibility for an intended
future use?
void CalculateMarshallingSize(Counter& cntr) const;
};
And the Middle file is:
tst_shepherd
(auto_ptr<vector<mytype> >, auto_ptr<uint32_t>, auto_ptr<mytype>)
}
Is this a constructor call? I don't understand the
syntax, but I also couldn't find a matching c'tor
in your definition of tst_shepherd given here:
The output is:
// Generated by the C++ Middleware Writer version 1.11
#include <memory>
#include <vector>
#include <tst.hh>
#include <MarshallingFunctions.hh>
#include <ReceiveCompressedBuffer.hh>
#include <SendCompressedBuffer.hh>
extern uint32_t msg_length_max;
struct tst_shepherd
{
void
Send(SendCompressedBuffer* buf, const auto_ptr<vector<mytype> >&
abt1,
const auto_ptr<uint32_t>& abt2, const auto_ptr<mytype>& abt3)
{
[snipping away everything that is not resolved by your former
definitions]
}
template <typename B>
void
Receive(B* buf, auto_ptr<vector<mytype> >& abt1, auto_ptr<uint32_t>&
abt2, auto_ptr<mytype>& abt3)
{
uint32_t headCount[1];
vector<mytype>* raw1 = new vector<mytype>;
This looks like a potential memory leak, because I don't
see any guarantee that the following code will not
throw an exception. Why do you not store the pointer into
either of an std::auto_ptr or std::unique_ptr?
buf->Give(headCount[0]);
raw1->reserve(raw1->size() + headCount[0]);
while (headCount[0] > 0) {
--headCount[0];
mytype rep3(buf);
raw1->push_back(rep3);
}
abt1.reset(raw1);
This saving is too late. If you would have stored raw1 in
a previous std::auto_ptr raw1, you could replace this by
abt1.reset(raw1.release());
uint32_t* raw3 = new uint32_t;
Same exception-safety problem. Store the memory
*immediately* in a smart pointer
buf->Give(*raw3);
abt2.reset(raw3);
mytype* raw4 = new mytype(buf);
abt3.reset(raw4);
This looks OK.
}
};
uint16_t const mytype_num = 7001;
template <typename B>
inline
mytype::mytype(B* buf)
{
buf->Give(c_);
uint32_t* raw5 = new uint32_t;
Same exception-safety problem.
buf->Give(*raw5);
a_.reset(raw5);
}
[..]
inline void
mytype::SendTypeNum(SendCompressedBuffer* buf) const
{
buf->Receive(&mytype_num, sizeof(mytype_num));
}
inline void
mytype::SendMemberData(SendCompressedBuffer* buf) const
{
complexSend(buf, c_);
buf->Receive(a_.get(), sizeof(uint32_t));
}
-----------------------------------------------------------------------
I've only confirmed that the output compiles correctly
on g++ 4.4.2. I'd like to hear ideas on what could be
done to improve the implementation. In particular, I
wonder if the Receive function and mytype's stream
constructor are correct and efficient.
I concentrated on the aspects that can be deduced
without knowing the details of the framework.
If you want to
dig into the details, there's an archive here --http://webEbenezer.net/build_integration.html--
that has everything needed to compile the above
code. The implementation for unique_ptr is the
same, except it pulls in the file "utility" rather than
"memory."
You need to include header <memory> for std::unique_ptr
as well. AFAIK this was so from the initial proposal
of std::unique_ptr on, and it this is still true for
the recent working draft.
HTH & Greetings from Bremen,
Daniel Kr?gler
--
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