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<TITLE>MPI_Grequest_start</TITLE>
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MPI_Grequest_start
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Create and return a user-defined request
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Synopsis
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int MPI_Grequest_start(MPI_Grequest_query_function * query_fn,
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MPI_Grequest_free_function * free_fn,
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MPI_Grequest_cancel_function * cancel_fn,
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void *extra_state, MPI_Request * request)
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Input Parameters
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query_fn callback function invoked when request status is queried (function)
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free_fn callback function invoked when request is freed (function)
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cancel_fn callback function invoked when request is cancelled (function)
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extra_state Extra state passed to the above functions.
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Output Parameters
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request Generalized request (handle)
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Notes on the callback functions
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The return values from the callback functions must be a valid MPI error code
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or class. This value may either be the return value from any MPI routine
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(with one exception noted below) or any of the MPI error classes.
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For portable programs, <tt>MPI_ERR_OTHER</tt> may be used; to provide more
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specific information, create a new MPI error class or code with
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<tt>MPI_Add_error_class</tt> or <tt>MPI_Add_error_code</tt> and return that value.
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The MPI standard is not clear on the return values from the callback routines.
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However, there are notes in the standard that imply that these are MPI error
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codes. For example, pages 169 line 46 through page 170, line 1 require that
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the <tt>free_fn</tt> return an MPI error code that may be used in the MPI completion
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functions when they return <tt>MPI_ERR_IN_STATUS</tt>.
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The one special case is the error value returned by <tt>MPI_Comm_dup</tt> when
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the attribute callback routine returns a failure. The MPI standard is not
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clear on what values may be used to indicate an error return. Further,
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the Intel MPI test suite made use of non-zero values to indicate failure,
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and expected these values to be returned by the <tt>MPI_Comm_dup</tt> when the
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attribute routines encountered an error. Such error values may not be valid
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MPI error codes or classes. Because of this, it is the user's responsibility
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to either use valid MPI error codes in return from the attribute callbacks,
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if those error codes are to be returned by a generalized request callback,
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or to detect and convert those error codes to valid MPI error codes (recall
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that MPI error classes are valid error codes).
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Thread and Interrupt Safety
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This routine is thread-safe. This means that this routine may be
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safely used by multiple threads without the need for any user-provided
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thread locks. However, the routine is not interrupt safe. Typically,
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this is due to the use of memory allocation routines such as <tt>malloc
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</tt>or other non-MPICH runtime routines that are themselves not interrupt-safe.
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Notes for Fortran
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All MPI routines in Fortran (except for <tt>MPI_WTIME</tt> and <tt>MPI_WTICK</tt>) have
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an additional argument <tt>ierr</tt> at the end of the argument list. <tt>ierr
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</tt>is an integer and has the same meaning as the return value of the routine
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in C. In Fortran, MPI routines are subroutines, and are invoked with the
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<tt>call</tt> statement.
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All MPI objects (e.g., <tt>MPI_Datatype</tt>, <tt>MPI_Comm</tt>) are of type <tt>INTEGER
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</tt>in Fortran.
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Errors
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All MPI routines (except <tt>MPI_Wtime</tt> and <tt>MPI_Wtick</tt>) return an error value;
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C routines as the value of the function and Fortran routines in the last
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argument. Before the value is returned, the current MPI error handler is
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called. By default, this error handler aborts the MPI job. The error handler
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may be changed with <tt>MPI_Comm_set_errhandler</tt> (for communicators),
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<tt>MPI_File_set_errhandler</tt> (for files), and <tt>MPI_Win_set_errhandler</tt> (for
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RMA windows). The MPI-1 routine <tt>MPI_Errhandler_set</tt> may be used but
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its use is deprecated. The predefined error handler
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<tt>MPI_ERRORS_RETURN</tt> may be used to cause error values to be returned.
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Note that MPI does not guarentee that an MPI program can continue past
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an error; however, MPI implementations will attempt to continue whenever
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possible.
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MPI_SUCCESS No error; MPI routine completed successfully.
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MPI_ERR_ARG Invalid argument. Some argument is invalid and is not
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identified by a specific error class (e.g., <tt>MPI_ERR_RANK</tt>).
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