Synchronous and asynchronous operation

Chapter 2, Developing applications using XTI or TLI

Some of the functions in XTI can operate either synchronously or asynchronously. In synchronous mode, a function call does not return until the operation can be completed (or until an error is detected). For example, if a process calls t_rcv in synchronous mode and no data is available, the call blocks until data arrives at the transport endpoint. On the other hand, if the process calls t_rcv in asynchronous mode and no data is available, the call returns immediately with a value of -1 and the global variable t_errno is set to TNODATA. It is then up to the process to decide when and how to try again and call t_rcv later.

The functions that can operate either synchronously or asynchronously are:

t_connect
t_rcvconnect
t_listen
t_rcv
t_rcvudata
t_snd
t_sndudata

A process usually indicates whether these functions will operate synchronously or asynchronously be setting the oflag argument to t_open to O_NONBLOCK. See the t_open manual page for for more information.