To: J3                                                     J3/26-218
From: Malcolm Cohen
Subject: Interp F23/028 on NOTIFY WAIT
Date: 2026-October-23


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NUMBER: F23/028
TITLE: Is NOTIFY WAIT permitted everywhere?
KEYWORDS: NOTIFY WAIT, CRITICAL, PURE, SIMPLE
DEFECT TYPE: Erratum
STATUS: J3 consideration in progress
REFERENCES: 24-007

QUESTION:

NOTIFY WAIT does (a special form of) cross-image synchronisation, but
does not appear to have any limit on where it may appear.

EVENT WAIT does a similarly special form of synchronisation, but as it
is an image control statement, there are limits on its appearance.

A reference to a collective subroutine - which also has a certain
amount of synchronisation (mostly internal) - is not an image control
statement, but has similar limits on its appearance.

It would appear to be highly desirable to prohibit NOTIFY WAIT from
contexts where the change of deadlock is increased, for example, in a
CRITICAL construct.

Introducing synchronisation delays into pure procedures would seem to
be undesirable, and depending on variable definition on other images
is clearly contrary to the design of simple procedures.

Should there be some limits on where NOTIFY WAIT may appear, perhaps
similar to those on collective subroutine invocations?

ANSWER:

Yes, NOTIFY WAIT should be prohibited from problematic contexts.

An edit is provided to correct this oversight.

EDIT to 24-007.

[215:11+] 11.6 NOTIFY WAIT statement, after C1178
            "A notify-variable... coindexed object."
          insert new constraint
   "C1178a A NOTIFY WAIT statement shall not appear in a context where
           an image control statement is not permitted to appear."

ALTERNATIVE EDIT to 24-007.

[347:2] 15.7 Pure procedures, constraint C15109,
        after "image control statement (11.7.1)"
        insert "or a NOTIFY WAIT statement (11.6)".
{This only prohibits NOTIFY WAIT from two problematic contexts.}

SUBMITTED BY: Malcolm Cohen

HISTORY: 26-nnn   m241  Submitted

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