# 18.2.114. shmem_long_cswap

shmem_int_cswap(3), shmem_int4_cswap(3), shmem_int8_cswap(3), shmem_long_cswap(3), shmem_longlong_cswap(3) - Performs an atomic conditional swap to a remote data object

## 18.2.114.1. SYNOPSIS

C or C++:

    #include <mpp/shmem.h>

    int shmem_int_cswap(int *target, int cond, int value, int pe)

    long shmem_long_cswap(long *target, long cond, long value,
      int pe)

    long long shmem_longlong_cswap(longlong *target,
      longlong cond, longlong value, int pe)

Fortran:

    INCLUDE "mpp/shmem.fh"

    INTEGER pe

    INTEGER(KIND=4) SHMEM_INT4_CSWAP
    ires = SHMEM_INT4_CSWAP(target, cond, value, pe)

    INTEGER(KIND=8) SHMEM_INT8_CSWAP
    ires = SHMEM_INT8_CSWAP(target, cond, value, pe)

## 18.2.114.2. DESCRIPTION

The conditional swap routines conditionally update a target data object on an arbitrary processing element (PE) and return the prior contents of the data object in one atomic operation.

The arguments are as follows:

target

  The remotely accessible integer data object to be updated on the remote PE. If you are using C/C++, the type of target should match that implied in the SYNOPSIS section. If you are using the Fortran compiler, it must be of type integer with an element size of 4 bytes for SHMEM_INT4_ADD and 8 bytes for SHMEM_INT8_ADD.

value

  The value to be atomically added to target. If you are using C/C++, the type of value should match that implied in the SYNOPSIS section. If you are using Fortran, it must be of type integer with an element size of target.

pe

  An integer that indicates the PE number upon which target is to be updated. If you are using Fortran, it must be a default integer value.

target

  The remotely accessible integer data object to be updated on the remote PE. If you are using C/C++, the data type of target should match that implied in the SYNOPSIS section. If you are using Fortran, it must be of the following type:

  SHMEM_INT4_CSWAP: 4-byte integer

  SHMEM_INT8_CSWAP: 8-byte integer

cond

  cond is compared to the remote target value. If cond and the remote target are equal, then value is swapped into the remote target. Otherwise, the remote target is unchanged. In either case, the old value of the remote target is returned as the function return value. cond must be of the same data type as target.

value

  The value to be atomically written to the remote PE. value must be the same data type as target.

pe

  An integer that indicates the PE number upon which target is to be updated. If you are using Fortran, it must be a default integer value.

## 18.2.114.3. NOTES

The term remotely accessible is defined in intro_shmem(3).

## 18.2.114.4. RETURN VALUES

The contents that had been in the target data object on the remote PE prior to the conditional swap.

## 18.2.114.5. EXAMPLES

The following call ensures that the first PE to execute the conditional swap will successfully write its PE number to race_winner on PE 0.

    main()
    {
      static int race_winner = -1;
      int oldval;

      shmem_init();
      oldval = shmem_int_cswap(&race_winner, -1, shmem_my_pe(), 0);
      if (oldval == -1)
        printf("pe %d was first\n",shmem_my_pe());
    }

See also

intro_shmem(3) shmem_cache(3) shmem_swap(3)