Forcing Records To Disc

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).