What does "REALTIME"/"Realtime Interfaces" mean in the man pages?

cjappl

Hi all,

I was wondering if you knew what "REALTIME" meant when it was included in various BSD man pages.

For example:

> man 2 aio_return | head
AIO_RETURN(2)                 System Calls Manual                AIO_RETURN(2)

NAME
     aio_return – retrieve return status of asynchronous I/O operation
     (REALTIME)
> man 2 sigaction | grep -i realtime -A 4
     Realtime Interfaces:

     aio_error(), sigpause(), aio_return(), aio_suspend(), sem_post(),
     sigset().
> apropos realtime | head
aio_cancel(2)            - cancel an outstanding asynchronous I/O operation (REALTIME)
aio_error(2)             - retrieve error status of asynchronous I/O operation (REALTIME)
aio_read(2)              - asynchronous read from a file (REALTIME)
aio_return(2)            - retrieve return status of asynchronous I/O operation (REALTIME)
aio_suspend(2)           - suspend until asynchronous I/O operations or timeout complete (REALTIME)
aio_write(2)             - asynchronous write to a file (REALTIME)

These can be found online at places like:
https://man.bsd.lv/FreeBSD-11.1/aio_return.2
https://man.freebsd.org/cgi/man.cgi?sigaction

And seem to be shared across the BSD variants.

In audio code (where I come from), system calls a typically disallowed as they have non-deterministic execution times. I have not seemed to find any info to say definitively what "REALTIME" means on these man pages.

Thanks

rvp

cjappl This comes from POSIX. See 2.1.5.2 XSI Option Groups where under Realtime we read:

Where entire functions are included in the Option Group, the NAME section is marked with REALTIME.

Under the BSDs, none of these functions imply any sort of hard-realtime guarantee. (POSIX just provides a way to do real-time programming, using these functions, if the OS does have real-time support.)

cjappl

rvp Thank you, great resource I wasn't aware of.

Going to dig in a bit and may be back with more questions.