hello Joaquin
You have to lockguard every access to the container; note this also includes, for instance, container traversal with iterators, i.e. iterator displacement. Strictly speaking, iterator dereference should also be lockguarded, although I can say unofficially that unguarded dereference is OK.
can you explain a litle more? as I konw from STL, multiple readers is ok. reading and inserting a new object does't invalidate iterators(for pointer-based conteiners offcourse,list, map etc...) a concurrent read and insert in multi_index are not (safely)possible? I mean there might be an iterator invalidation? offcourse there is a chance for a 'dirty-read' but this for the domain of the aplication if it is a problem and not for multi_index. thanks.