If a process calls an intrinsic to perform an I/O and
it encounters an EOF condition, it will either return
a CCG condition code or wait in the intrinsic until the
EOF condition is resolved. (See "EOF Conditions" in Chapter 3.)
In some applications, it is useful that the process always
wait instead of receiving a CCG.
It may be known that another process
will eventually open the file and satisfy the blocked I/O request.
MPE/iX lets the process request this
extended wait mode
through FCONTROL with a controlcode of 45.
Extended wait always starts out disabled,
but both readers and writers
can enable or disable it.
If extended wait is explicitly enabled, the process
always waits on an EOF condition. If extended wait
is explicitly disabled, the process will not wait on an EOF
condition unless there is an "opposite accessor" to
the file. In the default condition (extended wait is not
explicitly enabled or disabled), the process will wait if there
is an opposite accessor, or if this is the first I/O to the file.
Another feature of extended wait also concerns opposite
accessors. If a process is waiting for action by an opposite
accessor, and the last opposite accessor closes the file,
this will cause an EOF and "wake up" the waiting process.
Refer to the discussion of "EOF Conditions" in
Chapter 3 for more information about this feature.
Also, see Example B-2 in Appendix B.
