Message files reside primarily in buffers, and they
can lose data
in the event of a system crash.
For applications that
must use message files and must be "crash-proof,"
MPE/iX provides a way to force the data to disc.
This is done by using FCONTROL with a controlcode of 6.
Either readers or writers can call this intrinsic.
It forces all buffers to be written to disc and the disc
file label to be updated.
This causes several disc I/Os and, therefore,
takes a relatively long time.
It must be done after each FWRITE to be most effective,
and even then there is a "window"
between the FWRITE and
the FCONTROL
during which a crash would cause the record to be lost.
Remember that IPC is designed to be a fast, efficient means of
passing messages between processes.
If the task the application is performing
is really event logging, and it must be highly crash-resistant,
you should consider using "circular files" or other files with
FSETMODE. (FSETMODE is ignored for message files.)
For more information about FSETMODE, refer to
Accessing Files (32650-90017) and the MPE/iX Intrinsics
Reference Manual (32650-90028).
