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DFASY exit routine z/OS Communications Server: SNA Programming SC27-3674-00 |
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The DFASY exit routine provides a way for VTAM® to notify an application program that an
expedited-flow data-flow-control request has arrived. The requests
that can be received by an application program in a DFASY exit are:
For information on all of these requests, see Summary of control requests and indicators. See DFSYN, DFASY, and RESP types of RUs for information on the DFSYN, DFASY, and RESP types of RUs. If a DFASY exit routine is specified in an NIB EXLST or in an ACB EXLST applicable to the session whenever an expedited-flow data-flow-control request arrives, VTAM can schedule that DFASY exit routine. The detailed manner in which VTAM handles DFASY input is shown in Figure 1 and Figure 2. If an NIB exit routine is specified, it is always scheduled, whereas a specified ACB exit routine is scheduled only if the following conditions exist:
Using a DFASY exit routine is an alternative to getting each expedited-flow data-flow-control request with RECEIVE RTYPE=DFASY. The advantages and disadvantages of the two alternatives are discussed in Explicit RECEIVEs and EXLST exit routines. For a DFASY exit routine, information about the request that has
been received is available in a read-only RPL provided by VTAM. This RPL resides in read-only VTAM storage and that cannot be
used by RPL-based macroinstructions. The following are also true for
this RPL:
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