ATOMIC_CAS (The GNU Fortran Compiler)

### 8.34 `ATOMIC_CAS` — Atomic compare and swap ¶

Synopsis:

  `CALL ATOMIC_CAS (ATOM, OLD, COMPARE, NEW [, STAT])`

Description:

  `ATOMIC_CAS` compares the variable ATOM with the value of COMPARE; if the value is the same, ATOM is set to the value of NEW. Additionally, OLD is set to the value of ATOM that was used for the comparison. 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`.

Class:

  Atomic subroutine

Arguments:

  ATOM | Scalar coarray or coindexed variable of either integer type with `ATOMIC_INT_KIND` kind or logical type with `ATOMIC_LOGICAL_KIND` kind.
  OLD | Scalar of the same type and kind as ATOM.
  COMPARE | Scalar variable of the same type and kind as ATOM.
  NEW | Scalar variable of the same type as ATOM. If kind is different, the value is converted to the kind of ATOM.
  STAT | (optional) Scalar default-kind integer variable.

Example:

      program atomic
        use iso_fortran_env
        logical(atomic_logical_kind) :: atom[*], prev
        call atomic_cas (atom[1], prev, .false., .true.)
      end program atomic

Standard:

  TS 18508 or later

See also:

  `ATOMIC_DEFINE` — Setting a variable atomically,
  `ATOMIC_REF` — Obtaining the value of a variable atomically,
  `ISO_FORTRAN_ENV`