!standard 9.10(6.1/1)                                        07-10-24    AI05-0072-1/01
!class binding interpretation 07-10-24
!status ARG Approved  9-0-0  06-11-10
!status work item 07-10-24
!status received 07-10-23
!priority Low
!difficulty Easy
!qualifier Error
!subject Termination only signals 'Terminated when it is True

!summary

A task A signals another task B only when B reads A'Terminated as True (or the
equivalent call to Ada.Task_Identification).

!question

Section 9.10 defines the notion of one action "signaling"
another. If A1 "signals" A2 then we know that A1
precedes A2. 9.10(6.1/1) has added task termination
to this list, where A1 is termination, and A2 is
the evaluation of T'Terminated (or the equivalent
call on Is_Terminated). But this is only a "signal"
if the evaluation returns True. The wording should reflect
that.

!recommendation

(See Summary.)

!wording

Modify 9.10(6.1/1) as follows:

  * If A1 is the termination of a task T, and A2 is either
    {an}[the] evaluation of the expression T'Terminated {that
    results in True,} or a call to Ada.Task_Identification.
    Is_Terminated with an actual parameter that identifies
    T {and a result of True} (see C.7.1).

!discussion

If T'Terminated returns False, that says nothing interesting about the state of T.

!corrigendum 9.10(6.1/1)

@drepl
@xbullet<If A1 is the termination of a task T, and A2 is either
the evaluation of the expression T'Terminated or a call to
Ada.Task_Identification.Is_Terminated with an actual parameter
that identifies T (see C.7.1).>
@dby
@xbullet<If A1 is the termination of a task T, and A2 is either
an evaluation of the expression T'Terminated that results in True,
or a call to
Ada.Task_Identification.Is_Terminated with an actual parameter
that identifies T and a result of True (see C.7.1).>

!ACATS Test

This is testable, but the ARG voted not to test it in AI95-00118
(which originated the wording that this AI is correcting). Note that a test is
unlikely to detect any errors - even an implementation which gets this wrong
probably would pass a test like the one in the example of AI95-00118.

!appendix

From: Tucker Taft
Sent: Tuesday, October 23, 2007  3:35 PM

Section 9.10 defines the notion of one action "signaling"
another.  If A1 "signals" A2 then we know that A1
precedes A2.  6.1/1 has added task termination
to this list, where A1 is termination, and A2 is
the evaluation of T'Terminated (or the equivalent
call on Is_Terminated).  But this is only a "signal"
if the evaluation returns *True*.

So 6.1/1 should probably be revised as follows:

  * If A1 is the termination of a task T, and A2 is either
    the evaluation of the expression T'Terminated {that
    results in True,} or a call to Ada.Task_Identification.
    Is_Terminated with an actual parameter that identifies
    T {and a result of True} (see C.7.1).

****************************************************************

From: Tucker Taft
Sent: Tuesday, October 23, 2007  3:46 PM

Actually, the wording makes more sense if we replace
"either the evaluation of ..." with "either *an* evaluation
of ..." since the next part says "or *a* call ...".

Pick those nits!

****************************************************************