On Sun, Nov 22, 2009 at 9:08 PM, Vicente Botet Escriba <vicente.botet@wanadoo.fr> wrote:
Hi,
I don't know if I have already requested that but ...
Is there any deep reason to don't provide the equivalent of the free functions lock, try_lock
My guesses at the reasons:
Non-member function lock(Lockable1,Lockable2,...) Non-member function lock(begin,end)
Locking a bunch of locks is a recipe for deadlock. Do we lock them in order? Then hold lock1, lock2, waiting to get lock3? Sounds dangerous. On the other hand, I suppose you could argue that using these functions (exclusively) could guarantee that locks were always locked in the same order (thus preventing deadlock)?
Non-member function try_lock(Lockable1,Lockable2,...) Non-member function try_lock(begin,end)
Sounds even scarier - after trying lock1, do you try lock2? - so you don't get lock1, you do get lock2, other thread gets the opposite == deadlock.
to unlock multiple lockables?
Non-member function unlock(Lockable1,Lockable2,...) Non-member function unlock(begin,end)
Thanks, Vicente --
Only other reason would be because they are not common enough, and easy enough to write on your own (using for_each, etc) for when you do need them. Oh, and lastly, because in general direct calls to lock/unlock are discouraged (although at times useful/necessary) and scope_lock is preferred. So if you really wanted multiple locks, a multi_lock class should be used. It's lock() function would lock a set of locks, etc. Then use scope_lock. Tony