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

Hi, On Wed, May 14, 2008 at 7:44 PM, Anthony Williams wrote:

Igor R. writes:

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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: it might have to allocate a new chunk of memory for the vector, in which case it will have to move all the existing elements to the new memory, and free the old one.

The write locks and read locks in your code are identical (shared mutex). On a call that does a push into the vector, you are modifying data or doing a write. You should upgrade the lock you are holding from a read to a write lock by a call to lock_upgrade (gets the thread ability to gain exclusive lock) followed by unlock_upgrade_and_lock() (gives up the ability and gains the exclusive lock atomically) (I may be wrong here, requesting others to chip in), do the push and call to unlock_upgrade(). That will be a true implementation of single write and multiple reader paradigm. -dhruva -- Contents reflect my personal views only!