1MPI_Sendrecv(3) LAM/MPI MPI_Sendrecv(3)
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6 MPI_Sendrecv - Sends and receives a message
7
9 #include <mpi.h>
10 int MPI_Sendrecv(void *sbuf, int scount, MPI_Datatype sdtype,
11 int dest, int stag, void *rbuf, int rcount,
12 MPI_Datatype rdtype, int src, int rtag,
13 MPI_Comm comm, MPI_Status *status)
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16 sbuf - initial address of send buffer (choice)
17 scount - number of elements in send buffer (integer)
18 sdtype - type of elements in send buffer (handle)
19 dest - rank of destination (integer)
20 stag - send tag (integer)
21 rcount - number of elements in receive buffer (integer)
22 rdtype - type of elements in receive buffer (handle)
23 src - rank of source (integer)
24 rtag - receive tag (integer)
25 comm - communicator (handle)
26
29 rbuf - initial address of receive buffer (choice)
30 status - status object (Status). This refers to the receive operation.
31 Can also be the MPI constant MPI_STATUS_IGNORE , if the return
32 status is not desired.
33
36 To dispell a common misconception: src and dest do not have to be the
37 same. Additionally, a common mistake when using this function is to
38 mismatch the tags with the source and destination ranks, which can
39 result in deadlock.
40 This function is guaranteed not to deadlock in situations where pairs
42 of blocking sends and receives may deadlock. For example, the follow‐
43 ing code may deadlock if all ranks in MPI_COMM_WORLD execute it simul‐
44 taneously
45 int rank, size, to, from;
47 MPI_Comm_rank(MPI_COMM_WORLD, &rank);
48 MPI_Comm_size(MPI_COMM_WORLD, &size);
49 to = (rank + 1) % size;
50 from = (rank + size - 1) % size;
51 MPI_Send(send_buffer, ..., to, tag, MPI_COMM_WORLD);
52 MPI_Recv(recv_buffer, ..., from, tag, MPI_COMM_WORLD);
53 If even one rank's MPI_Send blocks and never completes, the entire
56 operation may deadlock. One alternative is to use MPI_Sendrecv in this
57 situation because it is guaranteed not to deadlock.
58
61 All MPI routines in Fortran (except for MPI_WTIME and MPI_WTICK ) have
62 an additional argument ierr at the end of the argument list. ierr is
63 an integer and has the same meaning as the return value of the routine
64 in C. In Fortran, MPI routines are subroutines, and are invoked with
65 the call statement.
66 All MPI objects (e.g., MPI_Datatype , MPI_Comm ) are of type INTEGER in
68 Fortran.
69
72 If an error occurs in an MPI function, the current MPI error handler is
73 called to handle it. By default, this error handler aborts the MPI
74 job. The error handler may be changed with MPI_Errhandler_set ; the
75 predefined error handler MPI_ERRORS_RETURN may be used to cause error
76 values to be returned (in C and Fortran; this error handler is less
77 useful in with the C++ MPI bindings. The predefined error handler
78 MPI::ERRORS_THROW_EXCEPTIONS should be used in C++ if the error value
79 needs to be recovered). Note that MPI does not guarantee that an MPI
80 program can continue past an error.
81 All MPI routines (except MPI_Wtime and MPI_Wtick ) return an error
83 value; C routines as the value of the function and Fortran routines in
84 the last argument. The C++ bindings for MPI do not return error val‐
85 ues; instead, error values are communicated by throwing exceptions of
86 type MPI::Exception (but not by default). Exceptions are only thrown
87 if the error value is not MPI::SUCCESS .
88 Note that if the MPI::ERRORS_RETURN handler is set in C++, while MPI
91 functions will return upon an error, there will be no way to recover
92 what the actual error value was.
93 MPI_SUCCESS
94 - No error; MPI routine completed successfully.
95 MPI_ERR_COMM
96 - Invalid communicator. A common error is to use a null commu‐
97 nicator in a call (not even allowed in MPI_Comm_rank ).
98 MPI_ERR_COUNT
99 - Invalid count argument. Count arguments must be non-negative;
100 a count of zero is often valid.
101 MPI_ERR_TYPE
102 - Invalid datatype argument. May be an uncommitted MPI_Datatype
103 (see MPI_Type_commit ).
104 MPI_ERR_TAG
105 - Invalid tag argument. Tags must be non-negative; tags in a
106 receive ( MPI_Recv , MPI_Irecv , MPI_Sendrecv , etc.) may also
107 be MPI_ANY_TAG . The largest tag value is available through the
108 the attribute MPI_TAG_UB .
109 MPI_ERR_RANK
111 - Invalid source or destination rank. Ranks must be between
112 zero and the size of the communicator minus one; ranks in a
113 receive ( MPI_Recv , MPI_Irecv , MPI_Sendrecv , etc.) may also
114 be MPI_ANY_SOURCE .
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119 MPI_Sendrecv_replace
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123 For more information, please see the official MPI Forum web site, which
124 contains the text of both the MPI-1 and MPI-2 standards. These docu‐
125 ments contain detailed information about each MPI function (most of
126 which is not duplicated in these man pages).
127 http://www.mpi-forum.org/
129
133 The LAM Team would like the thank the MPICH Team for the handy program
134 to generate man pages ("doctext" from ftp://ftp.mcs.anl.gov/pub/sow‐
135 ing/sowing.tar.gz ), the initial formatting, and some initial text for
136 most of the MPI-1 man pages.
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139 sendrecv.c
140LAM/MPI 7.1.2 2/23/2006 MPI_Sendrecv(3)