[97] | 1 | .\"Copyright 2007-2008 Sun Microsystems, Inc. |
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| 2 | .\" Copyright (c) 1996 Thinking Machines Corporation |
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| 3 | .TH MPI_Wait 3 "Dec 08, 2009" "1.4" "Open MPI" |
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| 4 | .SH NAME |
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| 5 | \fBMPI_Wait\fP \- Waits for an MPI send or receive to complete. |
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| 6 | |
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| 7 | .SH SYNTAX |
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| 8 | .ft R |
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| 9 | .SH C Syntax |
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| 10 | .nf |
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| 11 | #include <mpi.h> |
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| 12 | int MPI_Wait(MPI_Request *\fIrequest\fP, MPI_Status\fI *status\fP) |
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| 13 | |
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| 14 | .SH Fortran Syntax |
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| 15 | .nf |
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| 16 | INCLUDE 'mpif.h' |
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| 17 | MPI_WAIT(\fIREQUEST, STATUS, IERROR\fP) |
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| 18 | INTEGER \fIREQUEST, STATUS(MPI_STATUS_SIZE), IERROR\fP |
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| 19 | |
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| 20 | .SH C++ Syntax |
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| 21 | .nf |
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| 22 | #include <mpi.h> |
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| 23 | void Request::Wait(Status& \fIstatus\fP) |
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| 24 | |
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| 25 | void Request::Wait() |
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| 26 | |
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| 27 | .SH INPUT PARAMETER |
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| 28 | .ft R |
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| 29 | .TP 1i |
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| 30 | request |
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| 31 | Request (handle). |
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| 32 | .sp |
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| 33 | .SH OUTPUT PARAMETERS |
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| 34 | .ft R |
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| 35 | .TP 1i |
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| 36 | status |
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| 37 | Status object (status). |
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| 38 | .ft R |
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| 39 | .TP 1i |
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| 40 | IERROR |
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| 41 | Fortran only: Error status (integer). |
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| 42 | |
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| 43 | .SH DESCRIPTION |
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| 44 | .ft R |
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| 45 | 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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| 46 | .sp |
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| 47 | 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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| 48 | .sp |
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| 49 | 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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| 50 | .sp |
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| 51 | 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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| 52 | |
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| 53 | .SH NOTES |
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| 54 | 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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| 55 | .sp |
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| 56 | Example: Simple usage of nonblocking operations and MPI_Wait. |
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| 57 | .sp |
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| 58 | .nf |
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| 59 | CALL MPI_COMM_RANK(comm, rank, ierr) |
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| 60 | IF(rank.EQ.0) THEN |
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| 61 | CALL MPI_ISEND(a(1), 10, MPI_REAL, 1, tag, comm, request, ierr) |
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| 62 | **** do some computation **** |
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| 63 | CALL MPI_WAIT(request, status, ierr) |
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| 64 | ELSE |
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| 65 | CALL MPI_IRECV(a(1), 15, MPI_REAL, 0, tag, comm, request, ierr) |
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| 66 | **** do some computation **** |
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| 67 | CALL MPI_WAIT(request, status, ierr) |
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| 68 | END IF |
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| 69 | |
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| 70 | .SH ERRORS |
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| 71 | 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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| 72 | .sp |
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| 73 | Before the error value is returned, the current MPI error handler is |
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| 74 | called. By default, this error handler aborts the MPI job, except for |
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| 75 | I/O function errors. The error handler may be changed with |
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| 76 | MPI_Comm_set_errhandler, MPI_File_set_errhandler, or |
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| 77 | MPI_Win_set_errhandler (depending on the type of MPI handle that |
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| 78 | generated the request); the predefined error handler MPI_ERRORS_RETURN |
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| 79 | may be used to cause error values to be returned. Note that MPI does |
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| 80 | not guarantee that an MPI program can continue past an error. |
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| 81 | .sp |
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| 82 | Note that per MPI-1 section 3.2.5, MPI exceptions on requests passed |
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| 83 | to MPI_WAIT do not set the status.MPI_ERROR field in the returned |
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| 84 | status. The error code is passed to the back-end error handler |
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| 85 | and may be passed back to the caller through the return value of |
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| 86 | MPI_WAIT if the back-end error handler returns it. The |
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| 87 | pre-defined MPI error handler MPI_ERRORS_RETURN exhibits this |
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| 88 | behavior, for example. |
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| 89 | |
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| 90 | .SH SEE ALSO |
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| 91 | .ft R |
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| 92 | .sp |
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| 93 | MPI_Comm_set_errhandler |
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| 94 | .br |
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| 95 | MPI_File_set_errhandler |
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| 96 | .br |
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| 97 | MPI_Test |
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| 98 | .br |
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| 99 | MPI_Testall |
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| 100 | .br |
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| 101 | MPI_Testany |
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| 102 | .br |
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| 103 | MPI_Testsome |
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| 104 | .br |
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| 105 | MPI_Waitall |
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| 106 | .br |
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| 107 | MPI_Waitany |
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| 108 | .br |
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| 109 | MPI_Waitsome |
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| 110 | .br |
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| 111 | MPI_Win_set_errhandler |
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| 112 | .br |
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| 113 | |
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