HP 3000 Manuals HP 3000 Manuals
Asynchronous I/O
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).
NOTE A program does not need Privileged Mode capability in order to make
nowait NetIPC I/O requests.