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In order to perform nowait (asynchronous) socket I/O on an HP 3000, a process
must use the MPE XL IOWAIT and IODONTWAIT intrinsics.
IOWAIT and IODONTWAIT behave in the same way except that, in
the first case, the calling process must wait until the I/O operation is
complete; in the second case, control is immediately returned to the calling
process. One of these intrinsics must be called at some point after a nowait
I/O request. The calling process is not blocked after the initial nowait I/O
request.
IPCSEND, IPCRECV, and IPCRECVCN are normally
blocking calls. The calling process must wait until the send/receive request
is completed. A process can use IPCCONTROL to enable nowait I/O for a
specified call socket or VC socket descriptor. (Nowait mode remains in effect
until another IPCCONTROL call restores waited mode.) If a process
issues a nowait send or receive request, the request will be initiated but its
completion cannot be verified until IOWAIT or IODONTWAIT is
called. (For a nowait IPCRECVCN call, the data structures for the
connection are not created until IOWAIT is called.)
IPCCONNECT is always an unblocked call: control returns immediately
to the calling process, which must then call IPCRECV to complete the
connection.
Within the IOWAIT/IODONTWAIT intrinsic, the filenum
parameter should be given the appropriate call socket/VC socket descriptor
value. A value of zero indicates all sockets or files for which asynchronous
I/O requests have been issued. The function value returned by the intrinsic is
the descriptor (or file number) for which the I/O has completed (zero if no
completion).
The cstation (calling station) parameter returns a zero value
for any nowait receive request. For a nowait send request, bit one of the
parameter (the second highest bit) is set to on (all other bits off).
Therefore you can check bit one of the cstation parameter to
determine whether an input or an output operation completed.
The tcount parameter returns the amount of data received after
a nowait IPCRECV call. The target parameter is not currently used by
NetIPC.
The syntax for IOWAIT and IODONTWAIT is given here for
convenience. For further information on these intrinsics, please see the
MPE XL Intrinsics Reference Manual.
Steps for Programming with Asynchronous I/O
The following summarizes the steps to follow to have your program perform
asynchronous I/O:
- Create the call or VC socket with IPCCREATE,
IPCCONNECT, or IPCRECVCN.
- Enable nowait I/O with IPCCONTROL.
- Make a IPCRECVCN, IPCRECV, or IPCSEND NetIPC
call on the socket. The call will be asynchronous.
- Check the result code returned by the call to see if an
error occurred when the call was initiated.
- Call IOWAIT to cause the calling process to wait until the
NetIPC call completes or IODONTWAIT to see if the request has
completed.
- Once the asynchronous NetIPC call completes do the following:
- Check the condition code to see if an error occurred. If the
condition code=CCE, no error occurred. If the condition code
<> CCE, an error occurred.
- If an error occurred call IPCCHECK to determine the error
code (returned in the ipcerr parameter).
- If IOWAIT or IDONTWAIT was called with
filenum=0 or no filenum specified,
check the fnum value returned to determine the
socket for which I/O completed. (You can compare the
fnum value with the calldesc value
returned by IPCCREATE and the vcdesc
value returned by IPCCONNECT and IPCRECVCN.)
- If both a send and receive request were pending, check the
returned cstation value to determine if a send
completed (bit 1 is on) or a receive completed (bit 1 is off).
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NOTE: A program does not need Privileged Mode capability
in order to make nowait NetIPC I/O requests.
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