To: J3                                                     J3/23-208
From: John Reid & Brad Richardson
Subject: Interp on finalization
Date: 2023-August-11

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NUMBER: Fxx/xxx
TITLE: Finalizations and deallocations of coarrays
KEYWORDS: finalization, deallocation, coarray
DEFECT TYPE: Erratum
STATUS: J3 consideration in progress
REFERENCES: N2218 (FDIS)

INTRODUCTION
We are concerned about a single event causing several final subroutines
to be called. This can happen when a deallocate statement is executed
and it can happen on return from a procedure that has several local
objects that are finalizable. If finalizations that involve coarray
synchronizations are not invoked in the same order of all the images
of the current team, a race condition may occur. The note in 7.5.6.2
states "An implementation might need to ensure that when an event causes
more than one coarray to be deallocated, they are deallocated in the
same order on all images in the current team." We think that this
wording is based on the belief than many implementations will execute
the same object code on all active images so that no special attention
is needed to ensure that the final subroutines are called in the same
order on each image. We take the view that this should be a requirement.
We note that a final subroutine is permitted to contain image control
statements other than deallocate.

Similar considerations apply to deallocations.

QUESTION 1:
If an event causes more than one entity to be finalized, are these
finalizations made in the same order on all the images of the current
team?

QUESTION 2:
If an event causes more than one coarray to be deallocated, are these
deallocations made in the same order on all the images of the current
team?

ANSWER 1:
It was intended that if an event causes more than one entity to be
finalized, these finalizations made in the same order on all the images
of the current team. An edit is supplied to make this clear.

ANSWER 2:
It was intended that if an event causes more than one coarray to be
deallocated, these deallocatations made in the same order on all the
images of the current team. An edit is supplied to make this clear.


EDITS to N2218:

Question 1
In 7.5.6.2 The finalization process, at the end of the penultimate
sentence add ", but each image in the current team shall perform
the finalizations of those entities in the same order" so that the
sentence reads
"If several entities are to be finalized as a consequence of an
event specified in 7.5.6.3, the order in which they are finalized is
processor dependent, but each image in the current team shall perform
the finalizations of those entities in the same order."

Question 2
In 9.7.3.1 Form of the DEALLOCATE statement, final paragraph
after "statement" add "or as a consequence of an event specified in
9.7.3.2" and at the end of the sentence add ", but each image in the
current team shall perform the deallocations of those objects in the
same order" so that the paragraph reads
"When more than one allocated object is deallocated by execution of a
DEALLOCATE statement or as a consequence of an event specified in
9.7.3.2, the order of deallocation is processor dependent, but each
image in the current team shall perform the deallocations of those
objects in the same order."


SUBMITTED BY: John Reid & Brad Richardson

HISTORY: 23-xxx   m231  Submitted

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