"Peter Dimov" <pdimov@mmltd.net> writes:
Anthony Williams wrote:
Also, the semaphore version runs the function once, even if it throws an exception. The mutex version runs the function repeatedly if it throws an exception. The docs say that the function isn't allowed to throw, so this is a moot point.
I like the signature of call_once:
template<typename Function> void call_once(Function f, once_flag& flag)
but you need to fix the above behavior. The function is considered "run" only when it returns without an exception. So your semaphore version runs it zero times when an exception is thrown.
void f() { throw "something"; } int main() { try { f(); } catch(...){} } How many times has f() been *called*? One, or none? I find your concept of a function only having run if it exits without an exception odd. In my mind call_once means just that --- call the function once, not let it run without an exception once. The docs (http://www.boost.org/regression-logs/cs-win32_metacomm/doc/html/call_once.ht...) say that "the function func shall not throw exceptions", so handling it this way is certainly acceptable, IMO. Anthony -- Anthony Williams Software Developer