Question

I’m looking for something similar to the CopyOnWriteSet in Java, a set that supports add, remove and some type of iterators from multiple threads.

Answer 1

there isn’t one that I know of, the closest is in thread building blocks which has concurrent_unordered_map

The STL containers allow concurrent read access from multiple threads as long as you don’t aren’t doing concurrent modification. Often it isn’t necessary to iterate while adding / removing.

The guidance about providing a simple wrapper class is sane, I would start with something like the code snippet below protecting the methods that you really need concurrent access to and then providing ‘unsafe’ access to the base std::set so folks can opt into the other methods that aren’t safe. If necessary you can protect access as well to acquiring iterators and putting them back, but this is tricky (still less so than writing your own lock free set or your own fully synchronized set).

I work on the parallel pattern library so I’m using critical_section from VS2010 beta boost::mutex works great too and the RAII pattern of using a lock_guard is almost necessary regardless of how you choose to do this:

template <class T>
class synchronized_set
{
    //boost::mutex is good here too
    critical_section cs;
public:
    typedef set<T> std_set_type;
    set<T> unsafe_set;
    bool try_insert(...)
    {
        //boost has a lock_guard
        lock_guard<critical_section> guard(cs);
    }
};