Is there any way to check if an iterator is valid?

Question

For two threads manipulating a container map for example, what the correct way to test whether an iterator still valid (for performance reason) ?
Or would be of only in

Answer 1

If you implement a reader/writer solution, then you can have the writer set a flag that invalidates all the iterators of the readers.

http://en.wikipedia.org/wiki/Readers-writer_lock

I would not try to write to the map without synchronization, as Josh and Paul Tomblin mentioned.