To: J3                                                     J3/26-223
From: Soren Rasmussen & HPC
Subject: Edits to replace the SYNC ALL example
Date: 2026-October-26

1. Introduction
---------------

This paper contains edits to 11.7.3 SYNC ALL statement, paragraph 2, NOTE.

The issues with this example are
  1. Oversynchronizes, no obvious necessity for the first SYNC ALL.
  2. Performs a naive/non-scalable push-broadcast through a coarray, instead
     of calling CO_BROADCAST.


2. Edits to 26-007r2
--------------------

[248:12+] 11.7.3 SYNC ALL statement, paragraph 2, NOTE.

Replace the current example paragraph and code in the NOTE:

"
Here is a simple example of its use. Image 1 reads data and broadcasts it to
other images:
  REAL :: P[*]
  ...
  SYNC ALL
  IF (THIS_IMAGE()==1) THEN
    READ (*,*) P
    DO I = 2, NUM_IMAGES()
      P[I] = P
    END DO
  END IF
  SYNC ALL
"

The (unrelated) first paragraph of the Note should be preserved, or possibly
split into a separate Note.

with:

"
Here is a simple example of its use to synchronize a parallel halo exchange,
a common algorithm in scientific computing. Each image copies boundary values
from its two neighbors in a periodic one-dimensional decomposition. The first
SYNC ALL ensures that the neighbors have defined P(1:N) before the values are
copied; the second SYNC ALL ensures that all images have finished copying
before any image redefines P(1:N).

  REAL :: P(0:N+1)[*]    ! P(0) and P(N+1) hold copies of neighbor data
  INTEGER :: LEFT, RIGHT
  RIGHT = MOD (THIS_IMAGE(), NUM_IMAGES()) + 1   ! Periodic neighbors
  LEFT = MOD (THIS_IMAGE() - 2 + NUM_IMAGES(), NUM_IMAGES()) + 1
  ... ! Initialize the local data in P(1:N)
  SYNC ALL
  P(0) = P(N)[LEFT]
  P(N+1) = P(1)[RIGHT]
  SYNC ALL
"