Re: Ada Tasks vs Linux processes

[Jeffrey Carter <jeffrey.carter@boeing.com>]

tmoran@acm.org wrote:
> 
> >As far as delay 0.0 is concerned, it should yield the CPU to another
> >task, if there's one ready to run.  Generally, though, I use
> >delay Duration'Small instead of delay 0.0;
>   LRM D.9(7) says the implementation must document the minimum delay
> value that actually causes the task to block, while D.9(5) says a
> delay of zero does not block, but is only "potentially blocking".
> Even among compilers that don't implement Annex D, delay 0.0 usually
> does not unnecessarily block, while any positive delay usually blocks
> for two clock ticks, which on some systems can be a surprisingly long
> time.

Indeed. The Verdix compiler for SCO UNIX responded to "delay
Duration'Small;" by delaying until the next clock tick. Since the clock
ticked at 1 Hz, this corresponded to an average delay of 0.5 seconds. I
saw some very slow code that resulted from the GRACE components using
"delay Duration'Small;" to obtain a unique timestamp.

Jeffrey Carter