Re: Ada and Unix--Blocked Tasks

[esosun!esosun.css.gov@seismo.css.gov (Howard E. Turner, Jr.)]

	stachour@sctc.com (Paul Stachour) writes:

        [ lots deleted HET]

	    But tasking IS a part of Ada.  I should be able to expect
	that any environment that that supports Ada, should be able to
	support tasks.  Furthermore, that if I do ANYTHING in that task
	(including a call on an OS-specific function) that could block,
	that my task might block.  But I should be able to expect that
	the other tasks DO NOT BLOCK just because the OS decides to block
	one of the tasks.

        [ lots deleted HET]

I think the key phrase here is "..I do ANYTHING in that task
(including a call on an OS-specific function) that could block,...".  If
the compiler vendor provided you with an interface to an OS-specific
function, then I would agree with your expectations, however, if you
call an OS function that blocks (implying the entire process), then
I would disagree with your expectations.  When you go outside the bounds
of the language, e.g pragma interface, to get to another language, you
must handle anything that arises.  This includes signals, blocking I/O, etc.

	"Tasking IS a part of Ada."  But it is not a part of the
OS (usually).  The OS (except for maybe Rational's) has no notion 
of Ada tasking, so why would you expect it not to block the entire process?
In particular, Ada tasking is not a part of either VMS or Unix.  Neither
OS will recognize the difference between an executable generated from C or 
Ada or any other language.  Why would you expect the OS to handle executables
derived from Ada source any differently than from C?

Normally, compiler vendors provide a package(s) that support task 
blocking system calls instead of process blocking system calls.  These
are provided in addition to the the process blocking calls, which are
sometimes used.

Howard Turner
howard@esosun.css.gov
619.458.2654
SAIC   San Diego, CA USA