Why UNIX doesn't support event?

[Y. Rock Lee]

Most of real time OS's support event on the application level.
Inside UNIX KERNEL, one can also sleep on an event(address)
and expect to be waken up later by someone else.
But, on the user level a process can only sleep on TIME.

Of course, it can be simulated on the user level to have
a process sleep on an "event" and be waken up by a signal.
I just wonder why UNIX doesn't want to give a user process 
the option to sleep on an event in addition to time?
It doesn't seem to be very hard to me to add this feature
to UNIX (forget the "real time" part, we don't want to change 
the scheduler). What is the philosophy behind the design of
system call sleep()?
Thanks in advance.

Rock


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Y. Rock Lee       (614) 860-4774
AT&T Bell Labs.   Columbus, Ohio
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