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C Library Functions  - atomic_fetch_or (3)

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NAME

ATOMIC_FETCH_OR(3) - [ATOMIC:BIT MANIPULATION] Atomically fetch and perform a bitwise OR operation

SYNOPSIS

call atomic_fetch_or(atom, value, old [,stat] )

         subroutine atomic_fetch_or(atom, value, old, stat)

CHARACTERISTICS

DESCRIPTION

ATOMIC_FETCH_OR(ATOM, VALUE, OLD, STAT) atomically stores the value of ATOM in OLD and performs a bitwise OR operation between ATOM and VALUE, storing the result in ATOM.

When STAT is present and the invocation was successful, it is assigned the value 0. If it is present and the invocation has failed, it is assigned a positive value; in particular, for a coindexed ATOM, if the remote image has stopped, it is assigned the value of iso_fortran_env’s stat_stopped_image and if the remote image has failed, the value stat_failed_image.

The result is the bitwise OR (e.g., 1000 OR 0011 = 1011).

It is useful for setting bit flags atomically.

OPTIONS

o	ATOM : Scalar coarray or coindexed variable of integer type with ATOMIC_INT_KIND kind.
o	VALUE : Scalar of the same type as ATOM. If the kind is different, the value is converted to the kind of ATOM.
o	OLD : Scalar of the same type and kind as ATOM. Receives the value of ATOM before the operation.
o	STAT : (optional) Scalar default-kind integer variable. Set to 0 on success, or a positive value on failure.

EXAMPLES

Sample program:

    program demo_atomic_fetch_or
    use iso_fortran_env
    implicit none
    integer(atomic_int_kind) :: flags[*], old
    integer :: stat, me

      if (this_image() == 1) flags = int(b’1000’, atomic_int_kind)
      sync all

      me = this_image()
      call atomic_fetch_or(flags[1], int(b’0011’, atomic_int_kind), old, stat)

      if (stat /= 0) print *, "Image", me, ": Failed with STAT =", stat
      print *, "Image", me, ": Old =", old
      sync all

      if (this_image() == 1) print *, "Final flags:", flags

    end program demo_atomic_fetch_or

Expected Output (4 images, order varies)

        > Image 1: Old = 8
        > Image 2: Old = 11
        > Image 3: Old = 11
        > Image 4: Old = 11
        > Final flags: 11

STANDARD

TS 18508

SEE ALSO

ATOMIC_DEFINE(3), ATOMIC_OR(3), ISO_FORTRAN_ENV(3),

ATOMIC_FETCH_ADD(3), ATOMIC_FETCH_AND(3),

ATOMIC_FETCH_XOR(3)

See ISO_FORTRAN_ENV for constants like ATOMIC_INT_KIND, STAT_STOPPED_IMAGE, and STAT_FAILED_IMAGE.

Fortran intrinsic descriptions

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Nemo Release 3.1

atomic_fetch_or (3)

June 29, 2025

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