Invalid rtems_id?

[Thomas Dörfler]

Joel,

Joel Sherrill schrieb:
>
> An invalid ID or an invalid ID check or both?
>
> I would lean to both.
>   
Yes, I think we need a value to initialize application variables, and we
need a method to detect, whether a ID is valid. A typical use would be
to check, whether a ID holding variable has yet been initialized, or the
corresponding OS object has yet been created.
> But I think that technically, I would say that an id with
> 0xffff0000 is more reliably invalid.  That would let us
> max out the api, class, and node portions of the id
> with an index of 0 which is never valid except in the
> case of RTEMS_SELF which is 0x0.
>   
In that aspect, it is a bit of a shame that we can't use the value "0x0"
as the "invalid ID". In many situations you can use uninitialied global
variables and find out, whether they hold valid data. The C standard
guarantees, that an uninitialized global pointer variable holds a NULL
pointer, which is used as a "invalid" placeholder. If the same where
true for RTEMS object IDs, things like the "task_id" arrays in the
testsuite would hold invalid IDs by default (and not the "RTEMS_SELF"
constant).

So my proposal would be to define the invalid ID to be 0x0, and
RTEMS_SELF as 0xffff0000 (0r 0xff00):

#define RTEMS_INVALID_ID 0x0
#define RTEMS_SELF 0xffff0000

Any comments on that?

wkr,
Thomas.


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