Re: [Boost-users] is read/write mutex example correct

From: Kevin Heifner (heifnerk_at_[hidden])
Date: 2008-05-14 10:24:04

Igor R. wrote:
>  >
>  > The problem with this code is that you are returning a reference
>  > to data that might be immediately invalidated. A push_back via
>  > another thread can cause the referenced memory to no longer be valid.
> 
> Does push_back() really invalidate iterators to *previous* vector elements?!

Yes, and I quote the spec for insert which push_back() is based 
on: "Remarks: Causes reallocation if the new size is greater than 
the old capacity. If no reallocation happens, all the iterators 
and references before the insertion point remain valid."

So unless you set capacity of the vector so that it never grows 
then push_back() can invalidate a held reference.

Also it probably should be noted that even if you setup capacity 
so that the vector never grows and only allowed push_back() you 
still need mutex guards around any access to the shared object.

KevinH
-- 
Kevin Heifner  heifner @ ociweb.com  http://heifner.blogspot.com
           Object Computing, Inc. (OCI) www.ociweb.com