Re: Tasking performance between Ada83 and Ada95

[bobduff@world.std.com (Robert A Duff)]

In article <dewar.866376446@merv>, Robert Dewar <dewar@merv.cs.nyu.edu> wrote:
>However, these days, more and more work is done on multi-processors, and
>then of course you have no choice if you want to distribute tasks across
>processors other than to use the system level threads. Furthermore, the
>efficiency hit from operating these threads on separate processors may
>indeed be significant.

Are you saying it's impossible to write an Ada run-time system that does
parallelism without using operating system threads (on a Unix-like OS)?
That's not true -- I've done it.  I wrote an Ada 83 RTS that ran on a
parallel shared-memory machine where the OS had no threads support.  So
we created one Unix process per CPU (you need a way to know how many
CPUs there are).  Almost all memory in all the processes was mapped to
the same place.  And then the task scheduler decided which task to run
in which process according to the usual priority rules.  Of course,
non-blocking I/O required writing Text_IO (etc) in terms of system calls
that don't block, but interrupt when the I/O is done.

- Bob