Re: delay until and GNAT

[rracine@draper.com (Roger Racine)]

>  Does  someone  know  the   upper bound  on the lateness of  delay  until
>and delay relative
> for  Gnat  implement.  on  Win95 , WinNT   or  Linux.

>   Thanks.

There have been some replies to this, but let me rephrase the question, and 
then answer it, as best I can.  My guess is that he really wants to know the 
following:

If he is the only user on the system and is running his program in the 
foreground with nothing else running (except OS processes), and his highest 
priority task executes a "delay" or "delay until" statement, what is the upper 
bound on the actual delay, for some processor speed?

The three platforms you mentioned are not real-time operating systems, and 
therefore have some possible problems with this metric.  I have read technical 
reports that state that Windows NT and Linux each have system calls that, if 
called by a low-priority task or an OS process, have "unbounded" delays 
associated with them.  I have seen nothing on Win95.  Therefore, even though, 
normally the delay on the Windows platforms will be very close to the "clock 
tick" time (0.01 seconds?), every once in a great while, even if the machine 
is not connected to a network, it might take much longer.

On Linux, it depends on the runtime system you are using.  If you use the FSU 
runtime, there are even more possibilities of long blocking times, since every 
system call will block all tasks.  Using the "native" version, priorities do 
not work correctly unless you run as root (Linux threads are implemented as 
each thread being a separate process, and normal users are not allowed to run 
with multiple priorities).  And even running as root, ACT can not guarantee 
correct adherance to the Ada standard.

Please note that all of the problems are associated with the operating 
system(s), not GNAT.  The bottom line is: if you want to use multitasking, in 
any language, and want an upper bound on timing, use a real-time operating 
system.

That is one (more) interpretation of what was asked.

Roger Racine