To: J3                                                     J3/24-145
From: John Reid & Reinhold Bader
Subject: Interp. on allocation segments
Date: 2024-June-24
References: 24-007

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NUMBER: F23/xxx
TITLE: Segments associated with allocation
KEYWORDS: segment, allocate, coarray
DEFECT TYPE: Clarification
STATUS: J3 consideration in progress

QUESTION:

Is it possible for a coarray to be allocated on an image in the current
team without there being a corresponding allocated coarray on another
active image in the current team?

For example, consider the program

PROGRAM ALLOCATION
   IMPLICIT NONE
   INTEGER :: I
   REAL, ALLOCATABLE :: A[:]
   ALLOCATE (A[*])
   A = THIS_IMAGE()
   SYNC ALL
   DO I = 2,THIS_IMAGE()
      IF (A[I]/=I) WRITE(*,*) "Value incorrect on image", I
   END DO
   DEALLOCATE (A)
END

Is it possible that an execution of the IF statement fails because the
coarray A has already been deallocated on image I?

ANSWER:

Unfortunately, the standard says nothing about the ordering of the
execution of an ALLOCATE or DEALLOCATE statement on an image with respect
to the execution of the segment that precedes the corresponding statement
on another image. The means that it is possible for a coarray to be
allocated on an image in the current team without there being a
corresponding allocated coarray on another active image in the current
team. Also, it is possible for the example to fail.

This was not intended and edits are provided to correct this.


EDITS to 24-007

[149:1] In "9.7.1.2 Execution of an ALLOCATE statement", para 5, after
sentence 3 "If no other error condition ... this team." add
"Execution of the statement on an image shall be delayed until the
segment preceding the same statement has been executed on all active
images in the current team."

[152:10] In "9.7.3.2 Deallocation of allocatable variables", after
sentence 3 "If no other error condition ... this team." add
"Execution of the statement on an image shall be delayed until the
segment preceding the same statement has been executed on all active
images in the current team."