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!standard 9.10(6.1/1) 07-12-13 AI05-0072-1/02
!class binding interpretation 07-10-24
!status Amendment 201Z 08-11-26
!status WG9 Approved 08-06-20
!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)

Replace the paragraph:

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);

by:

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).

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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!

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