Re: [boost] Preliminary Review Request: boost-memory

From: shiwei xu (xushiweizh_at_[hidden])
Date: 2008-05-06 22:47:00

Your question is very interesting. I thought it before. In fact I don't know
a perfect solution. If the constructor of an object throws, should the
destructor be called?

class Foo
{
private:
    A m_a;
    B m_b;
    C m_c;

public:
    Foo() {
        m_a.init();
        m_b.init();
        thow std::exception("error");
        m_c.init();
    }
    ~Foo() {
        ...
    }
};

Suppose we initialized m_a and m_b. m_c was uninitialized when the exception
throws. If the destructor is called, it may cause a crash. If the destructor
isn't called, the allocated memory of m_a and m_b will be leaked.

I choose to call the destructor because I think that a crash is easy to be
detected and be solved.

On Wed, May 7, 2008 at 9:34 AM, Steven Watanabe <watanabesj_at_[hidden]>
wrote:

> AMDG
>
> shiwei xu wrote:
> > typedef void (*DestructorType)(void* data);
> >
> > concept GCAllocator
> > {
> >     // Allocate memory without given a cleanup function
> >     void* allocate(size_t cb);
> >
> >     // Allocate memory with a cleanup function
> >     void* allocate(size_t cb, DestructorType fn);
> >
> >     // Cleanup and deallocate all allocated memory by this GC Allocator
> >     void clear();
> >
> >     // Swap two GCAllocator instances
> >     void swap(GCAllocator& o);
> > };
> >
>
> I have a question about exception safety.  Suppose that
> I specify a destructor when I allocate memory, and then,
> the constructor of the object throws.  Is there any way
> to prevent the destructor from being called, given this interface?
> Otherwise, the destructor might end up being called on
> an object that was never initialized.
>
> In Christ,
> Steven Watanabe
>