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<H1 id="MPI_Compare_and_swap">MPI_Compare_and_swap</H1>
Perform one-sided atomic compare-and-swap.
<H2>Synopsis</H2>
<PRE>
int MPI_Compare_and_swap(const void *origin_addr, const void *compare_addr,
void *result_addr, MPI_Datatype datatype, int target_rank,
MPI_Aint target_disp, MPI_Win win)
</PRE>
<P>
This function compares one element of type datatype in the compare buffer
compare_addr with the buffer at offset target_disp in the target window
specified by target_rank and win and replaces the value at the target with the
value in the origin buffer origin_addr if the compare buffer and the target
buffer are identical. The original value at the target is returned in the
buffer result_addr.
<P>
<H2>Input Parameters</H2>
<DL>
<DT><B>origin_addr </B> <DD> initial address of buffer (choice)
<DT><B>compare_addr </B> <DD> initial address of compare buffer (choice)
<DT><B>result_addr </B> <DD> initial address of result buffer (choice)
<DT><B>datatype </B> <DD> datatype of the entry in origin, result, and target buffers (handle)
<DT><B>target_rank </B> <DD> rank of target (nonnegative integer)
<DT><B>target_disp </B> <DD> displacement from start of window to beginning of target buffer (non-negative integer)
<DT><B>win </B> <DD> window object (handle)
</DL>
<P>
<H2>Notes</H2>
This operation is atomic with respect to other "accumulate" operations.
<P>
The parameter datatype must belong to one of the following categories of
predefined datatypes: C integer, Fortran integer, Logical, Multi-language
types, or Byte as specified in Section 5.9.2 on page 176. The origin and result
buffers (origin_addr and result_addr) must be disjoint.
<P>
<H2>Notes for Fortran</H2>
All MPI routines in Fortran (except for <tt>MPI_WTIME</tt> and <tt>MPI_WTICK</tt>) have
an additional argument <tt>ierr</tt> at the end of the argument list. <tt>ierr
</tt>is an integer and has the same meaning as the return value of the routine
in C. In Fortran, MPI routines are subroutines, and are invoked with the
<tt>call</tt> statement.
<P>
All MPI objects (e.g., <tt>MPI_Datatype</tt>, <tt>MPI_Comm</tt>) are of type <tt>INTEGER
</tt>in Fortran.
<P>
<H2>Errors</H2>
<P>
All MPI routines (except <tt>MPI_Wtime</tt> and <tt>MPI_Wtick</tt>) return an error value;
C routines as the value of the function and Fortran routines in the last
argument. Before the value is returned, the current MPI error handler is
called. By default, this error handler aborts the MPI job. The error handler
may be changed with <tt>MPI_Comm_set_errhandler</tt> (for communicators),
<tt>MPI_File_set_errhandler</tt> (for files), and <tt>MPI_Win_set_errhandler</tt> (for
RMA windows). The MPI-1 routine <tt>MPI_Errhandler_set</tt> may be used but
its use is deprecated. The predefined error handler
<tt>MPI_ERRORS_RETURN</tt> may be used to cause error values to be returned.
Note that MPI does <em>not</em> guarentee that an MPI program can continue past
an error; however, MPI implementations will attempt to continue whenever
possible.
<P>
<DL>
<DT><B>MPI_SUCCESS </B> <DD> No error; MPI routine completed successfully.
</DL>
<DL>
<DT><B>MPI_ERR_ARG </B> <DD> Invalid argument. Some argument is invalid and is not
identified by a specific error class (e.g., <tt>MPI_ERR_RANK</tt>).
</DL>
<DL>
<DT><B>MPI_ERR_COUNT </B> <DD> Invalid count argument. Count arguments must be
non-negative; a count of zero is often valid.
</DL>
<DL>
<DT><B>MPI_ERR_OP </B> <DD> Invalid operation. MPI operations (objects of type <tt>MPI_Op</tt>)
must either be one of the predefined operations (e.g., <tt>MPI_SUM</tt>) or
created with <tt>MPI_Op_create</tt>.
</DL>
<DL>
<DT><B>MPI_ERR_RANK </B> <DD> Invalid source or destination rank. Ranks must be between
zero and the size of the communicator minus one; ranks in a receive
(<tt>MPI_Recv</tt>, <tt>MPI_Irecv</tt>, <tt>MPI_Sendrecv</tt>, etc.) may also be <tt>MPI_ANY_SOURCE</tt>.
</DL>
<DL>
<DT><B>MPI_ERR_TYPE </B> <DD> Invalid datatype argument. Additionally, this error can
occur if an uncommitted MPI_Datatype (see <tt>MPI_Type_commit</tt>) is used
in a communication call.
</DL>
<DL>
<DT><B>MPI_ERR_WIN </B> <DD> Invalid MPI window object
</DL>
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