To use no-wait I/O with SNA IMF, set bit 15 of the OPEN3270 flags parameter to 1. Call either IOWAIT or IODONTWAIT after each TRAN3270 or RECV3270 call to determine whether the requested I/O operation
is finished. IOWAIT suspends your program until the I/O operation
is complete. IODONTWAIT checks to see if I/O is complete but does not
wait for its completion.
Use IOWAIT or IODONTWAIT in addition to RECV3270 and TRAN3270, not instead of them.
As with standard wait I/O, a TRAN3270 request issued under no-wait I/O completes immediately;
that is, it does not wait for a response from the host. After a TRAN3270 call, issue either IOWAIT or IODONTWAIT to verify that the TRAN3270 request actually completed the I/O.
A RECV3270 request completes as soon as data is received
from the host. If the host sends data before RECV3270 is called, the data is stored in the internal
screen image. No further SNA IMF internal I/O processing of this
data is necessary; as soon as you call RECV3270 and IOWAIT or, they complete.
With no-wait I/O, some result codes normally returned to TRAN3270 and RECV3270 are returned in the cstation parameter of the IOWAIT or IODONTWAIT intrinsic instead. These result codes are listed
in the intrinsic descriptions, later in this chapter.
TRAN3270 and RECV3270 do not initiate I/O if any value other than zero is
returned in the result parameter. If your program receives a code other than
zero, do not call IOWAIT or IODONTWAIT. Resolve the error and reissue your call to TRAN3270 or RECV3270.
