To: J3                                                     J3/26-219r1
From: Malcolm Cohen
Subject: Interp F23/028 on NOTIFY_TYPE pointers
Date: 2026-October-28


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NUMBER: F23/029
TITLE: Can a variable of type NOTIFY_TYPE be a pointer?
KEYWORDS: NOTIFY_TYPE, POINTER
DEFECT TYPE: Erratum
STATUS: Passed by J3 meeting
REFERENCES: 24-007

QUESTION:

A named variable of type NOTIFY_TYPE cannot be a pointer, as it is
required to be a coarray (C854 says pointers cannot be coarrays).

However, a component of type NOTIFY_TYPE is apparently permitted to be
a pointer. This is problematic, as in:

    TYPE t
        TYPE(notify_type),POINTER :: p
    END TYPE
    TYPE(t) x[*]
    REAL y[*]

    ... assume that x%p becomes associated on the executing image,
    ... whether by allocation or pointer assignment

    y[n,NOTIFY=x%p] = 999

The assignment statement
   "increments the count of the corresponding notify variable on the
    image specified by the image selector"

But there is no corresponding notify variable, because x%p is not a
subobject of X, and therefore is not a coarray. That renders any use
of x%p for synchronisation non-conforming.

And that renders NOTIFY_TYPE pointer components useless, quite apart
from the inconsistency with not allowing them for named variables of
type NOTIFY_TYPE.

Another problematic case is:

    TYPE t
        TYPE(notify_type),POINTER :: p
    END TYPE
    TYPE(t) x
    TYPE(notify_type) :: z[*]
    REAL y[*]
    x%p => z

    y[n,NOTIFY=x%p] = 999

Is it the corresponding variable Z?

Are either of these examples supposed to be conforming?

ANSWER:

Yes, the first example should be conforming, but the second example
should not be conforming.

Edits are supplied to correct the situation.

EDIT to 24-007.

[145:10+] 9.6 Image selectors, after C934 "TEAM and TEAM_NUMBER...",
          insert new constraint:
   "C933a In a NOTIFY= image-selector-spec, the notify-variable shall
          be a coarray or a structure-component where one part-ref has
          a part-name that is a coarray."

[145:25-27] Same subclause, p4 "Execution of an assignment...",
            after "specified by the image selector" end the sentence,
            deleting the ", and" and capitalising the following "the",
            and insert a new sentence before that "The":
               "The indicated notify variable is the one that would be
                designated by a coindexed reference with an image
                selector applied to the coarray notify-variable, or to
                the part-ref of the notify-variable whose part-name is
                a coarray; where the image selector specifies the same
                image as the image selector on the variable.".
            This makes the whole paragraph read:
   "Execution of an assignment statement whose variable has a NOTIFY=
    specifier atomically increments the count of the indicated notify
    variable on the image specified by the image selector. The
    indicated notify variable is the one that would be designated by a
    coindexed reference with an image selector applied to the coarray
    notify-variable, or to the part-ref of the notify-variable whose
    part-name is a coarray; where the image selector specifies the
    same image as the image selector on the variable. The statement
    does not wait for that image to execute a corresponding NOTIFY
    WAIT statement."

SUBMITTED BY: Malcolm Cohen

HISTORY: 26-219   m241  Submitted
         26-219r1 m241  Passed as amended by J3 meeting 241.

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