Thanks for the response. I'm sorry, and perhaps I misunderstand, but I
believe your statement about inline operator new is incorrect. Unless I
misunderstand you, what you say is not supported by any existing
compiler nor is it supported by the C++ language standard. In summary,
the 'inline' keyword does not negate or obviate the One Definition
Rule. You can demonstrate the problem with the code below. Feel free to
correct any misunderstanding that I may have of your explanation.
I do not mean to criticize WebKit. We think it is a great thing which
in general is surprisingly well coded. We would love to work with any
resolution which has the desired effect in the way of memory management.
The error you get:
SomeLib.lib: error LNK2005:
"void * __cdecl operator new(unsigned int)" ([EMAIL PROTECTED]@Z) already
defined in main.obj
SomeLib.lib: error LNK2005: "void
__cdecl operator delete(void *)" ([EMAIL PROTECTED]@Z) already defined in
main.obj
Source code:
// Main.cpp
#include <stdlib.h>
extern void DoSomething();
void* operator new(size_t s) {
return malloc(s); }
void operator delete(void* p) {
free(p); }
void* operator new[](size_t s) {
return malloc(s); }
void operator delete[](void* p){
free(p); }
int main(int, char*[]) {
void* p = malloc(10);
free(p);
DoSomething();
return 0;
}
// SomeLib.cpp - compiled in a
separate lib
#include <stdlib.h>
inline void* operator new(size_t
s) { return malloc(s); }
inline void operator delete(void* p)
{ free(p); }
inline void* operator new[](size_t s)
{ return malloc(s); }
inline void operator delete[](void*
p) { free(p); }
void DoSomething(){
void* p = malloc(10);
free(p);
}
Thanks.
On 03/06/2008, at 21:13, Paul Pedriana wrote:
Thanks for the info. IMHO, tcmalloc is not
appropriate for console,
embedded, and mobile platforms. It trades space for speed, and that's
the opposite of what you want outside the desktop. This is why the
Nokia
S60 people replaced tcmalloc, for example.
As far as I can tell, Nokia's S60 port predates the adoption of
tcmalloc by WebKit. The code in their latest svn.webkit.org source
tree contains a variant of dlmalloc that was used up until Safari 2.0,
though I have not checked to see whether it is compiled in to their
build. That said, it is obvious that the space vs. speed tradeoffs
differ between devices, and that flexibility in the memory allocator
used is desirable.
Unfortunately, overriding operator new and
delete does not do the right
thing. These operators are application-global functions and when you
redirect them for one library you are thus redirecting them for the
entire rest of the app. Needless to say, that is a bad thing. In
console
and embedded development, as I note in the aforementioned paper, it is
typically verboten for a library to use operator new/delete.
On the platforms with which I am familiar, the implementation that I
linked to has no effect outside of the library in which it is defined.
I've not worked with consoles or embedded devices so the toolchain and
environment may differ there, but I would be a little surprised to see
an inline function that is implemented in a header become visible to an
object file that did not include the header.
Neither will you see professional commercial
software do this.
It's also a problem to have any calls to
system malloc at all, because often on
these platforms there is little or no memory available, as the
application has taken it all to distribute to private heaps as per
their
budget.
The direct calls are few and far between. They can easily be evaluated
to determine which, if any, have a legitimate need to call the system
allocator and the remainder updated to use "fastMalloc" / "fastFree".
I'd gladly review a patch that moves in this direction.
One simple and effective way to solve this
problem is to provide a
memory config header file which defines macros or templates which
replace new/delete, malloc/free. Instead of calling global new, WC_NEW
(e.g.) is called instead.
How does this differ from FastMalloc.h and "fastMalloc" / "fastFree"
that I described in my previous email, other than addressing the
perceived problem with "operator new" / "operator delete"?
This is how commercial-quality software is
done
Kind regards,
Mark Rowe
|
