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<H1 id="MPI_Wait">MPI_Wait</H1>
Waits for an MPI request to complete
<H2>Synopsis</H2>
<PRE>
int MPI_Wait(MPI_Request * request, MPI_Status * status)
</PRE>
<H2>Input Parameters</H2>
<DL>
<DT><B>request </B> <DD> request (handle)
</DL>
<P>
<H2>Output Parameters</H2>
<DL>
<DT><B>status </B> <DD> status object (Status). May be <tt>MPI_STATUS_IGNORE</tt>.
</DL>
<P>
<H2>Notes on the MPI_Status argument</H2>
<P>
The <tt>MPI_ERROR</tt> field of the status return is only set if
the return from the MPI routine is <tt>MPI_ERR_IN_STATUS</tt>. That error class
is only returned by the routines that take an array of status arguments
(<tt>MPI_Testall</tt>, <tt>MPI_Testsome</tt>, <tt>MPI_Waitall</tt>, and <tt>MPI_Waitsome</tt>). In
all other cases, the value of the <tt>MPI_ERROR</tt> field in the status is
unchanged. See section 3.2.5 in the MPI-1.1 specification for the
exact text.
<P>
For send operations, the only use of status is for <tt>MPI_Test_cancelled</tt> or
in the case that there is an error in one of the four routines that
may return the error class <tt>MPI_ERR_IN_STATUS</tt>, in which case the
<tt>MPI_ERROR</tt> field of status will be set. In that case, the value
will be set to <tt>MPI_SUCCESS</tt> for any send or receive operation that completed
successfully, or <tt>MPI_ERR_PENDING</tt> for any operation which has neither
failed nor completed.
<P>
<H2>Thread and Interrupt Safety</H2>
<P>
This routine is thread-safe. This means that this routine may be
safely used by multiple threads without the need for any user-provided
thread locks. However, the routine is not interrupt safe. Typically,
this is due to the use of memory allocation routines such as <tt>malloc
</tt>or other non-MPICH runtime routines that are themselves not interrupt-safe.
<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>
The <tt>status</tt> argument must be declared as an array of size <tt>MPI_STATUS_SIZE</tt>,
as in <tt>integer status(MPI_STATUS_SIZE)</tt>.
<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_REQUEST </B> <DD> Invalid <tt>MPI_Request</tt>. Either null or, in the case of a
<tt>MPI_Start</tt> or <tt>MPI_Startall</tt>, not a persistent request.
</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>
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