Le 26/06/13 18:03, Vicente Botet a écrit :
Ben Pope wrote
On 21/02/13 02:02, Vicente J. Botet Escriba wrote:
Hi,
boost::synchronized_value (not released yet [1][2][3]) is based on [4]. See below part of this paper adapted to the Boost.Thread interface.
Currently boost::synchronized_value is in addition Copyable and Swappable. I was wondering if it is worth adding value and move semantics to synchronized_value. Making it EqualityComparable, LessThanComparable and Movable if the underlying type satisfy these requirements will allow to store them on a Boost.Container/C++11 container.
Do you see something completely wrong with this addition? Has some of you had a need for this? Could you share the context? Sorry, I'm a bit late to the party and not really answering the question.
I can see the usefulness of synchronized_value for C++03, but not in C++11. Why?
It's just too easy to forget to call the synchronise() member:
boost::synchronized_value<std::queue<int>> synch_queue; if(!synch_queue->empty()) synch_queue->pop();
when was was meant was (excuse use of auto, I've become lazy):
boost::synchronized_value<std::queue<int>> synch_queue; { auto lock = synch_queue.synchronize(); if(!synch_queue->empty()) synch_queue->pop(); }
This is neither safe or efficient (2 lock/unlocks). this should be
boost::synchronized_value<std::queue<int>> synch_queue; { auto lock = synch_queue.synchronize(); if(!lock->empty()) lock->pop(); }
I think this should just not exist in C++11 and instead be replaced by something like monitor <T> described by Herb Sutter [1]:
monitor<std::queue<int>> synch_queue; queue([](std::queue& q) { if(!q.empty()) q.pop(); } Sorry I don't understand the syntax.
After looking at the slides I understand now what it means. I guess you meant sync_queue([](std::queue& q) { if(!q.empty()) q.pop(); } ); I like execute around a function locking pattern, and yes without lambdas this pattern is not practical, so no portable to C++03. Adding the function to synchronized_value would not be too hard. Best, Vicente