Re: using a new_handler
On May 21, 1:49 pm, desktop <f...@sss.com> wrote:
James Kanze wrote:
On May 20, 7:21 pm, desktop <f...@sss.com> wrote:
Ok the example I made was more or less based on Bjarne Stroustrup's
example on page 129 i the C++ Programming Language. His new_handler
looks like this:
void out_of_store() {
cerr << "operator new failed: out of store\n";
throw bad_alloc();
}
He also show a function that uses new:
void f() {
try{
for(;;) new char[10000];
}
catch(bad_alloc) {
cerr << "Memory exhausted!\n";
}
}
But I don't see why the out_of_store() function is needed if all
functions that uses new just makes sure to catch bad_alloc.
Probably, his goal was only to show how you can create a new
handler, not what it might be used for in practice. In this
exact example, for example, there really isn't much point in
using a new handler (and it's likely to fail anyway, at least on
some implementations, because cerr will also try to allocate
memory).
Would it not make more sense to make a new_handler that catches
bad_alloc and then omit the try/catch in all functions using new, since
the new_handler takes care of the catch for all new calls?
That's what I usually do. For various reasons, it's not
generally possible to reliably recover from insufficient memory.
My applications (large servers) generally run on dedicated
machines, with what should be sufficient memory; if memory runs
out, it's almost certainly because there is a memory leak, and
of course, at that point, recovery is impossible. But more
generally, not all systems reliably report out of memory, and
even less will allow you to intervene if you run out of memory
increasing the size of the stack, or something like that. So
you reserve a bit on the side, and install a new handler which
logs the problem, and aborts.
--
James Kanze (GABI Software) email:james.kanze@gmail.com
Conseils en informatique orient=E9e objet/
Beratung in objektorientierter Datenverarbeitung
9 place S=E9mard, 78210 St.-Cyr-l'=C9cole, France, +33 (0)1 30 23 00 34