  We describe several features of parallel or distributed asynchronous
iterative algorithms such as unbounded delays, possible out of order messages
or flexible communication. We concentrate on the concept of macroiteration
sequence which was introduced in order to study the convergence or termination
of asynchronous iterations. A survey of asynchronous iterations for convex
optimization problems is also presented. Finally, a new result of convergence
for parallel or distributed asynchronous iterative algorithms with flexible
communication for convex optimization problems and machine learning is
proposed.
