Hi, What if Block Pointer was single threaded for the moment? Would that prevent it from being part of Boost? A lot of applications are single threaded and could take advantage of it already. fast_pool_allocator is not multithread safe as well. The problem is the structure keeping track of each set, block_header, is dynamic (gets created and destroyed over and over) and to maintain a mutex in such conditions is not trivial. Thanks, -Phil