User`s guide

38 DC 900-1339H

FMP Programmer’s Guide

Note

For most applications, the FMP protocol requires Raw read and

write requests to specify protocol-speciﬁc information.

3.1.3 Blocking versus Non-blocking I/O

Note

Earlier Freeway releases used the term “synchronous” for blocking

I/O and “asynchronous” for non-blocking I/O. Some parameter

names reﬂect the previous terminology.

Non-blocking I/O applications are useful when doing I/O to multiple channels with a

single process where it is not possible to “block” on any one channel waiting for I/O

completion. Blocking I/O applications are useful when it is reasonable to have the call-

ing process wait for I/O completion.

In the Freeway environment, the term blocking I/O indicates that the

dlOpen, dlClose,

dlRead and dlWrite functions do not return until the I/O is complete. For non-blocking

I/O, these functions might return after the I/O has been queued at the client, but before

the transfer to Freeway is complete. The client must handle I/O completions at the soft-

ware interrupt level in the completion handler established by the

dlInit or dlOpen

function, or by periodic use of dlPoll to query the I/O completion status.

The

asyncIO DLI conﬁguration parameter speciﬁes whether an application session uses

blocking or non-blocking I/O. The

alwaysQIO DLI conﬁguration parameter further

qualiﬁes the operation of non-blocking I/O activity. Refer to the Freeway Data Link

Interface Reference Guide for more information.

The effects on different DLI functions, resulting from the choice of blocking or non-

blocking I/O, are explained in the Freeway Data Link Interface Reference Guide and

throughout this chapter as they relate to FMP.