If I bracket the write call with a mutex to protect the data block from corruption as it's actually being written does that interfere with the read operation? Presumably this needs to compare the write pointer with the read one to find out if there is anything to read. -- Will J Godfrey http://www.musically.me.uk Say you have a poem and I have a tune. Exchange them and we can both have a poem, a tune, and a song.