Re: better new delete
* Joe Greer:
cppquester@googlemail.com wrote in news:1188220750.006159.197410
@r29g2000hsg.googlegroups.com:
Hi Folks,
I just had the following idea for opertor new and delete
(I am sure I am not the first one, haven't seen it
so far though):
class A
{
std::vector< int> someData;
static std::stack used;
You need to give a type here.
public:
static void * operator new (size_t size);
static void operator delete (void *p, size_t size);
};
void* A::operator new(size_t sz)
{
void* res;
if( used.size() > 0)
{
res = used.back();
used.pop();
return res;
}
return ::new( sz);
}
void A::operator delete (void *p, size_t sz)
{
someData.clear();
used.push( p);
}
If there are a lot of instances of A to be allocated and freed all the
time,
could (would) this result in a performance gain compared to
the standard new/delete operator as system calls are avoided in most
cases?
Of course it is obvious that there is a certain memory overhead (for
the stack and as all As are never freed), but it looks to me that this
is a very easy way to gain a lot of performance potentially. Am I
missing something?
At first I didn't understand the point of someData, but now I think I
do. What you really want to do with your delete operator is:
void A::operator delete(void *p, size_t sz)
{
static_cast<A*>(p)->~A();
used.push(p);
}
Considering that original code would not compile, it isn't necessarily
bad to introduce additional undefined behavior.
However, the OP and other readers may get the impression that the above
would be a good idea.
So, to correct that impression: it's just Undefined Behavior, the object
has already been destroyed.
Cheers, & hth.,
- Alf
--
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