In this library, asynchronous socket operations are those member functions having prefix async_.

For an object s, a program may initiate asynchronous socket operations such that there are multiple simultaneously outstanding asynchronous operations.

When there are multiple outstanding asynchronous read operations on s:

— having no argument flags of type socket_base::message_flags, or

— having an argument flags of type socket_base::message_flags but where (flags & socket_base::message_out_of_band) == 0

then the buffers are filled in the order in which these operations were issued. The order of invocation of the completion handlers for these operations is unspecified.

When there are multiple outstanding asynchronous read operations on s having an argument flags of type socket_base::message_flags where (flags & socket_base::message_out_of_band) != 0 then the buffers are filled in the order in which these operations were issued.

When there are multiple outstanding asynchronous write operations on s, the buffers are transmitted in the order in which these operations were issued. The order of invocation of the completion handlers for these operations is unspecified.