|  | 
        In this section, synchronous socket operations are those
        member functions specified as two overloads, with and without an argument
        of type error_code&:
      
R f(A1 a1, A2 a2, ..., AN aN); R f(A1 a1, A2 a2, ..., AN aN, error_code& ec);
        For an object s, the conditions
        under which its synchronous socket operations may block the calling thread
        (C++Std [defns.block]) are determined as follows.
      
If:
        — s.non_blocking()
        == true,
      
        — the synchronous socket operation is specified in terms of a POSIX
        function other than poll()
        — that POSIX function lists EWOULDBLOCK
        or EAGAIN in its failure
        conditions, and
      
— the effects of the operation cannot be established immediately
then the synchronous socket operation shall not block the calling thread. [Note: And the effects of the operation are not established. —end note]
Otherwise, the synchronous socket operation shall block the calling thread until the effects are established.