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From: himel@mips.UUCP (Mark I. Himelstein)
Newsgroups: comp.lang.ada
Subject: Re: Microsoft OS/2 -- Ideal for Ada
Message-ID: <459@gumby.UUCP>
Date: Wed, 17-Jun-87 00:14:51 EDT
Article-I.D.: gumby.459
Posted: Wed Jun 17 00:14:51 1987
Date-Received: Sun, 21-Jun-87 08:51:14 EDT
References: <8706130340.AA00283@rand-unix.arpa> <928@bloom-beacon.MIT.EDU> <1624@aw.sei.cmu.edu>
Reply-To: himel@gumby.UUCP (Mark I. Himelstein)
Distribution: world
Organization: MIPS Computer Systems, Sunnyvale, CA
List-Id: <comp.lang.ada>

In article <1624@aw.sei.cmu.edu> firth@bd.sei.cmu.edu.UUCP writes:
...

>I agree that it is inappropriate to map Ada tasks into Unix processes.
>For one thing, the overhead is insupportable.

I agree too mainly due the horrible overhead of unix processes and the
shared nature of the ada memory model.


>Unfortunately, the alternative doesn't work either.  Two serious
>problems

I presume you mean multi-tasks within one unix process.



>(a) Unix does not provide asynchronous IO to a process.  If one Ada task
>    does a read() from the terminal, the whole program blocks.  And you
>    thought polling died out in the '60s?

BSD UNIX provides full asynchronous IO. This is done with ioctl's and fcntl's
and setting up a signal handler for SIGIO.


>(b) A large number of Unix system calls are not reentrant.  If one Ada
>    task is suspended in a malloc(), chaos can ensue.

Since Ada tasks would share memory, allocating from a shared heap like malloc
represents a critical region and other tasks should be blocked.

Mark I. Himelstein
decwrl!mips!himel