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C Library Functions  - atomic_define (3)

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NAME

ATOMIC_DEFINE(3) - [ATOMIC] Atomically define the value of a variable

SYNOPSIS

call atomic_define (atom, value [,stat] )

         subroutine atomic_define(atom, value, stat)

          TYPE(kind=atomic_KIND_kind) :: atom[*]
          TYPE(kind=KIND) :: value
          integer,intent(out),optional :: stat

CHARACTERISTICS

o	ATOM : Scalar coarray or coindexed variable of either integer type with ATOMIC_INT_KIND kind or logical type with ATOMIC_LOGICAL_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	STAT : (optional) Scalar default-kind integer variable.

DESCRIPTION

ATOMIC_DEFINE(ATOM, VALUE, STAT) atomically sets the value of ATOM to VALUE. This ensures thread-safe assignment in parallel environments.

Use for simple atomic assignments, unlike ATOMIC_CAS(3) which involves comparison.

Only one image should call ATOMIC_DEFINE(3) to avoid undefined behavior in this context.

OPTIONS

o	ATOM : Scalar coarray or coindexed variable to atomically assign the value VALUE to. kind.
o	VALUE : value to assign to ATOM
o	STAT : 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.

EXAMPLES

Sample program:

    program demo_atomic_define
      use iso_fortran_env
      implicit none
      integer(atomic_int_kind) :: counter[*]
      integer :: stat, me

      if (this_image() == 1) counter = 0
      sync all

      me = this_image()
      if (me == 2) call atomic_define(counter[1], 42, stat)

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

      if (this_image() == 1) print *, "Final counter:", counter
    end program demo_atomic_define

Expected Output (4 images)

        > Final counter: 42

STANDARD

Fortran 2008 ; with STAT, TS 18508

SEE ALSO

ATOMIC_REF(3), ATOMIC_CAS(3), ISO_FORTRAN_ENV(3), ATOMIC_ADD(3), ATOMIC_AND(3), ATOMIC_OR(3), ATOMIC_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_define (3)

June 29, 2025

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