118 строки
4.3 KiB
Plaintext
118 строки
4.3 KiB
Plaintext
.\" Copyright 2007-2008 Sun Microsystems, Inc.
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.\" Copyright (c) 1996 Thinking Machines Corporation
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.TH MPI_Wait 3 "#OMPI_DATE#" "#PACKAGE_VERSION#" "#PACKAGE_NAME#"
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.SH NAME
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\fBMPI_Wait\fP \- Waits for an MPI send or receive to complete.
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.SH SYNTAX
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.ft R
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.SH C Syntax
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.nf
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#include <mpi.h>
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int MPI_Wait(MPI_Request *\fIrequest\fP, MPI_Status\fI *status\fP)
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.fi
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.SH Fortran Syntax
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.nf
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INCLUDE 'mpif.h'
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MPI_WAIT(\fIREQUEST, STATUS, IERROR\fP)
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INTEGER \fIREQUEST, STATUS(MPI_STATUS_SIZE), IERROR\fP
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.fi
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.SH C++ Syntax
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.nf
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#include <mpi.h>
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void Request::Wait(Status& \fIstatus\fP)
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void Request::Wait()
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.fi
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.SH INPUT PARAMETER
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.ft R
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.TP 1i
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request
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Request (handle).
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.sp
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.SH OUTPUT PARAMETERS
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.ft R
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.TP 1i
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status
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Status object (status).
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.ft R
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.TP 1i
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IERROR
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Fortran only: Error status (integer).
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.SH DESCRIPTION
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.ft R
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A call to MPI_Wait returns when the operation identified by request is complete. If the communication object associated with this request was created by a nonblocking send or receive call, then the object is deallocated by the call to MPI_Wait and the request handle is set to MPI_REQUEST_NULL.
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.sp
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The call returns, in status, information on the completed operation. The content of the status object for a receive operation can be accessed as described in Section 3.2.5 of the MPI-1 Standard, "Return Status." The status object for a send operation may be queried by a call to MPI_Test_cancelled (see Section 3.8 of the MPI-1 Standard, "Probe and Cancel").
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.sp
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If your application does not need to examine the \fIstatus\fP field, you can save resources by using the predefined constant MPI_STATUS_IGNORE as a special value for the \fIstatus\fP argument.
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.sp
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One is allowed to call MPI_Wait with a null or inactive request argument. In this case the operation returns immediately with empty status.
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.SH NOTES
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Successful return of MPI_Wait after an MPI_Ibsend implies that the user send buffer can be reused i.e., data has been sent out or copied into a buffer attached with MPI_Buffer_attach. Note that, at this point, we can no longer cancel the send (for more information, see Section 3.8 of the MPI-1 Standard, "Probe and Cancel"). If a matching receive is never posted, then the buffer cannot be freed. This runs somewhat counter to the stated goal of MPI_Cancel (always being able to free program space that was committed to the communication subsystem).
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.sp
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Example: Simple usage of nonblocking operations and MPI_Wait.
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.sp
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.nf
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CALL MPI_COMM_RANK(comm, rank, ierr)
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IF(rank.EQ.0) THEN
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CALL MPI_ISEND(a(1), 10, MPI_REAL, 1, tag, comm, request, ierr)
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**** do some computation ****
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CALL MPI_WAIT(request, status, ierr)
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ELSE
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CALL MPI_IRECV(a(1), 15, MPI_REAL, 0, tag, comm, request, ierr)
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**** do some computation ****
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CALL MPI_WAIT(request, status, ierr)
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END IF
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.fi
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.SH ERRORS
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Almost all MPI routines return an error value; C routines as the value of the function and Fortran routines in the last argument. C++ functions do not return errors. If the default error handler is set to MPI::ERRORS_THROW_EXCEPTIONS, then on error the C++ exception mechanism will be used to throw an MPI::Exception object.
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.sp
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Before the error value is returned, the current MPI error handler is
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called. By default, this error handler aborts the MPI job, except for
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I/O function errors. The error handler may be changed with
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MPI_Comm_set_errhandler, MPI_File_set_errhandler, or
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MPI_Win_set_errhandler (depending on the type of MPI handle that
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generated the request); the predefined error handler MPI_ERRORS_RETURN
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may be used to cause error values to be returned. Note that MPI does
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not guarantee that an MPI program can continue past an error.
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.sp
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Note that per MPI-1 section 3.2.5, MPI exceptions on requests passed
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to MPI_WAIT do not set the status.MPI_ERROR field in the returned
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status. The error code is passed to the back-end error handler
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and may be passed back to the caller through the return value of
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MPI_WAIT if the back-end error handler returns it. The
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pre-defined MPI error handler MPI_ERRORS_RETURN exhibits this
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behavior, for example.
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.SH SEE ALSO
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.ft R
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.sp
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MPI_Comm_set_errhandler
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.br
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MPI_File_set_errhandler
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.br
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MPI_Test
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.br
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MPI_Testall
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.br
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MPI_Testany
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.br
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MPI_Testsome
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.br
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MPI_Waitall
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.br
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MPI_Waitany
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.br
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MPI_Waitsome
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.br
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MPI_Win_set_errhandler
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.br
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