On 4/22/11 5:21 PM, Iain Buclaw wrote:
== Quote from bearophile (bearophileh...@lycos.com)'s article
Timon Gehr:
But, as pointed out by Linus, the prime performance problem is _not_ the GC, but
the mindset that comes with it. Most programmers that "grew up" in a managed
environment tend to use very many "new" keywords all over their code, instead of
allocating large chunks of memory at once. (Java/C#/etc encourage you to do
this.)
In C99 (and Ada) you avoid the allocation of some dynamic arrays with new thanks
to variable length arrays.
Variable length arrays are just sugary syntax for a call to alloca.
Well in fairness they can be a fair amount more elaborate. The trouble
with alloca is that it's impossible to compose with. So in general you
need to write something like:
bool onStack = smallEnough(length * sizeof(T));
auto a = (cast(T*) (onStack ? alloca : malloc)(length * sizeof(T)));
scope(exit) if (!onStack) free(a.ptr);
initialize(enforce(a));
scope(exit) clear(a);
This block is difficult to factor out because of alloca.
Andrei
