On Mon, Nov 23, 2009 at 9:45 AM, Francois Barel <frabar666@gmail.com> wrote:
Anthony Williams wrote:
The current implementation handles exceptions "properly" in the sense that if the once function exits with an exception then it is not marked as called and another thread (possibly one of those waiting) will call it.
Does this mean the function will be called again? Isn't that disturbing for something named "call_once"?
I think the spec of the original POSIX pthread_once was that it was a thread 'cancellation point', and they decided that the function would be considered 'uncalled' on cancellation. For C++ the analog would be exceptions. But I agree, it doesn't match the name. In our case, if the function threw, it must have been *called*. Maybe it didn't 'complete' (depending on your definition of complete) but it was called. At times in the the past, I've toyed with having two functions - call_once() and complete_once() (implemented by a common function internally). But then complete_once() would imply recursion also, so I decided to separate the concepts. IMO, the big advantage of re-calling on exception is that the same exception would likely be thrown in each thread. Which is hard to do otherwise. Tony