Re: How to avoid repeated run-time lookup for the virtual function?
On 24/02/2012 23:50, GH wrote:
Hi all, I am trying to optimize a piece of code that looks like the
following:
struct Game;
struct PlayerBase { virtual void play(Game*) const = 0; ... };
template<unsigned int CATEGORY> struct Player : PlayerBase { virtual
void play(Game*) const; ... };
struct Game {
bool gameOver();
void start(const vector<PlayerBase*>& players) {
while (! gameOver()) { // (1)
for (vector<PlayerBase*>::const_iterator i=players.begin(); i!
=players.end(); ++i) // (2)
(*i)->play(this); // (3)
}
}
};
At (3), there is some overhead because of the virtual function play(),
which is quite significant when play() itself is simple. But the
runtime resolution for the virtual function for each element in the
vector needs to be done only once at the first iteration of loop (1).
Is there a good way to achieve that?
I would be amazed if the code being called to execute play() was simple,
but the overhead for a dynamic call is actually rather low on most
systems (equivalent to a single pointer dereference.) I think that it is
unlikely that there is a real use case where the overhead will be
significant.
Also note that in real code for this kind of thing the membership and
ordering of the vector is probably subject to change by another thread
(managing adding and removing players)
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