On Jul 13, 2004, at 12:06 PM, Peter Dimov wrote:
Yes, having both mutex and timed_mutex will satisfy our hypotheticals. However if mutex::timed_lock is required, timed_mutex makes no sense from specification point of view.
My bad. There are at least 3 important clients to consider: 1. Give me mutex::timed_lock(), but only if it doesn't cost much, else I want a compile time error. 2. Give me timed_mutex::timed_lock(). Gotta have it on every platform. 3. Give me mutex::lock(), and please make it as small and fast as possible. I'm putting this mutex into my objects, and I'll have container<my_object>, so minimal overhead in the mutex is important (I don't care about timed_lock(), never use it). Did I miss any? Have I enumerated any "clients" that anyone thinks don't exist, or exist in vanishingly small numbers? Personally I feel that 2 and 3 definitely exist in significant numbers. I'm not positive about 1, but readily admit that I wouldn't want to bet much that 1 exists in vanishingly small numbers.
I want the standard to require mutex::timed_lock, because if there is no such requirement, no implementation will provide it. Why bother? No points are taken off conformance tests, and the users can't really demand it, because it's not required.
I think you grossly understate the motivation of all the std::lib vendors I'm aware of today. While the Metrowerks implementation is quite clearly the best one available, ;-) all implementations are aggressively pursuing conformance, optimizations and extensions. I'm not aware of any mediocre implementations of the std::lib today (compared with say 7 years ago). And I'm also not aware of any std::lib vendor that isn't listening very closely to their customers. My compliments to my competitors. If an optional mutex::timed_lock() is a good idea, and if C++0X blesses the idea, and if a few customers of a specific vendor request it for a specific platform where it would indeed make sense, I can practically guarantee you it will be implemented. If on the other hand, mutex::timed_lock() is required, I can guarantee you that customer #3, on some platforms, is going to be a very unhappy camper. Unhappy enough to not use this library, and thus we will have failed. -Howard