if you don’t change the size anymore, it should be save.

But it’s saver to lock ;-)

If it’s guaranteed that the vector will never be resized, it should work.

As Gerolf said as long as you do not resize the vector (or call other methods that can change the memory layout such as reserve()) and you are sure that you are only reading from indexes that are not being written to at the same time (e.g. by using semaphores) it should be safe (I think) ;-).

Thank you for the answers!

No problem. Sounds like you could be a potential user of this class [qt.gitorious.org] that I wrote. I have a small wrapper around this class that makes it into a thread-safe container for the producer-consumer pattern.