251 lines
8.9 KiB
Groff
251 lines
8.9 KiB
Groff
.\" Man page generated from reStructuredText.
|
|
.
|
|
.TH "MPI_UNPACK" "3" "Feb 14, 2025" "" "Open MPI"
|
|
.
|
|
.nr rst2man-indent-level 0
|
|
.
|
|
.de1 rstReportMargin
|
|
\\$1 \\n[an-margin]
|
|
level \\n[rst2man-indent-level]
|
|
level margin: \\n[rst2man-indent\\n[rst2man-indent-level]]
|
|
-
|
|
\\n[rst2man-indent0]
|
|
\\n[rst2man-indent1]
|
|
\\n[rst2man-indent2]
|
|
..
|
|
.de1 INDENT
|
|
.\" .rstReportMargin pre:
|
|
. RS \\$1
|
|
. nr rst2man-indent\\n[rst2man-indent-level] \\n[an-margin]
|
|
. nr rst2man-indent-level +1
|
|
.\" .rstReportMargin post:
|
|
..
|
|
.de UNINDENT
|
|
. RE
|
|
.\" indent \\n[an-margin]
|
|
.\" old: \\n[rst2man-indent\\n[rst2man-indent-level]]
|
|
.nr rst2man-indent-level -1
|
|
.\" new: \\n[rst2man-indent\\n[rst2man-indent-level]]
|
|
.in \\n[rst2man-indent\\n[rst2man-indent-level]]u
|
|
..
|
|
.sp
|
|
\fI\%MPI_Unpack\fP — Unpacks a datatype into contiguous memory.
|
|
.SH SYNTAX
|
|
.SS C Syntax
|
|
.INDENT 0.0
|
|
.INDENT 3.5
|
|
.sp
|
|
.nf
|
|
.ft C
|
|
#include <mpi.h>
|
|
|
|
int MPI_Unpack(const void *inbuf, int insize, int *position,
|
|
void *outbuf, int outcount, MPI_Datatype datatype,
|
|
MPI_Comm comm)
|
|
.ft P
|
|
.fi
|
|
.UNINDENT
|
|
.UNINDENT
|
|
.SS Fortran Syntax
|
|
.INDENT 0.0
|
|
.INDENT 3.5
|
|
.sp
|
|
.nf
|
|
.ft C
|
|
USE MPI
|
|
! or the older form: INCLUDE \(aqmpif.h\(aq
|
|
MPI_UNPACK(INBUF, INSIZE, POSITION, OUTBUF, OUTCOUNT,
|
|
DATATYPE, COMM, IERROR)
|
|
<type> INBUF(*), OUTBUF(*)
|
|
INTEGER INSIZE, POSITION, OUTCOUNT, DATATYPE,
|
|
COMM, IERROR
|
|
.ft P
|
|
.fi
|
|
.UNINDENT
|
|
.UNINDENT
|
|
.SS Fortran 2008 Syntax
|
|
.INDENT 0.0
|
|
.INDENT 3.5
|
|
.sp
|
|
.nf
|
|
.ft C
|
|
USE mpi_f08
|
|
MPI_Unpack(inbuf, insize, position, outbuf, outcount, datatype, comm,
|
|
ierror)
|
|
TYPE(*), DIMENSION(..), INTENT(IN) :: inbuf
|
|
TYPE(*), DIMENSION(..) :: outbuf
|
|
INTEGER, INTENT(IN) :: insize, outcount
|
|
INTEGER, INTENT(INOUT) :: position
|
|
TYPE(MPI_Datatype), INTENT(IN) :: datatype
|
|
TYPE(MPI_Comm), INTENT(IN) :: comm
|
|
INTEGER, OPTIONAL, INTENT(OUT) :: ierror
|
|
.ft P
|
|
.fi
|
|
.UNINDENT
|
|
.UNINDENT
|
|
.SH INPUT PARAMETERS
|
|
.INDENT 0.0
|
|
.IP \(bu 2
|
|
\fBinbuf\fP: Input buffer start (choice).
|
|
.IP \(bu 2
|
|
\fBinsize\fP: Size of input buffer, in bytes (integer).
|
|
.IP \(bu 2
|
|
\fBoutcount\fP: Number of items to be unpacked (integer).
|
|
.IP \(bu 2
|
|
\fBdatatype\fP: Datatype of each output data item (handle).
|
|
.IP \(bu 2
|
|
\fBcomm\fP: Communicator for packed message (handle).
|
|
.UNINDENT
|
|
.SH INPUT/OUTPUT PARAMETER
|
|
.INDENT 0.0
|
|
.IP \(bu 2
|
|
\fBposition\fP: Current position in bytes (integer).
|
|
.UNINDENT
|
|
.SH OUTPUT PARAMETERS
|
|
.INDENT 0.0
|
|
.IP \(bu 2
|
|
\fBoutbuf\fP: Output buffer start (choice).
|
|
.IP \(bu 2
|
|
\fBierror\fP: Fortran only: Error status (integer).
|
|
.UNINDENT
|
|
.SH DESCRIPTION
|
|
.sp
|
|
Unpacks a message into the receive buffer specified by outbuf, outcount,
|
|
datatype from the buffer space specified by inbuf and insize. The output
|
|
buffer can be any communication buffer allowed in \fI\%MPI_Recv\fP\&. The input
|
|
buffer is a contiguous storage area containing insize bytes, starting at
|
|
address inbuf. The input value of position is the first location in the
|
|
input buffer occupied by the packed message. \fIposition\fP is incremented
|
|
by the size of the packed message, so that the output value of position
|
|
is the first location in the input buffer after the locations occupied
|
|
by the message that was unpacked. \fIcomm\fP is the communicator used to
|
|
receive the packed message.
|
|
.SH NOTES
|
|
.sp
|
|
Note the difference between \fI\%MPI_Recv\fP and \fI\%MPI_Unpack\fP: In \fI\%MPI_Recv\fP, the
|
|
\fIcount\fP argument specifies the maximum number of items that can be
|
|
received. The actual number of items received is determined by the
|
|
length of the incoming message. In \fI\%MPI_Unpack\fP, the count argument
|
|
specifies the actual number of items that are to be unpacked; the “size”
|
|
of the corresponding message is the increment in position. The reason
|
|
for this change is that the “incoming message size” is not predetermined
|
|
since the user decides how much to unpack; nor is it easy to determine
|
|
the “message size” from the number of items to be unpacked.
|
|
.sp
|
|
To understand the behavior of pack and unpack, it is convenient to think
|
|
of the data part of a message as being the sequence obtained by
|
|
concatenating the successive values sent in that message. The pack
|
|
operation stores this sequence in the buffer space, as if sending the
|
|
message to that buffer. The unpack operation retrieves this sequence
|
|
from buffer space, as if receiving a message from that buffer. (It is
|
|
helpful to think of internal Fortran files or sscanf in C for a similar
|
|
function.)
|
|
.sp
|
|
Several messages can be successively packed into one packing unit. This
|
|
is effected by several successive related calls to \fI\%MPI_Pack\fP, where the
|
|
first call provides position = 0, and each successive call inputs the
|
|
value of position that was output by the previous call, and the same
|
|
values for outbuf, outcount, and comm. This packing unit now contains
|
|
the equivalent information that would have been stored in a message by
|
|
one send call with a send buffer that is the “concatenation” of the
|
|
individual send buffers.
|
|
.sp
|
|
A packing unit can be sent using type MPI_Packed. Any point\-to\-point or
|
|
collective communication function can be used to move the sequence of
|
|
bytes that forms the packing unit from one process to another. This
|
|
packing unit can now be received using any receive operation, with any
|
|
datatype: The type\-matching rules are relaxed for messages sent with
|
|
type MPI_Packed.
|
|
.sp
|
|
A message sent with any type (including MPI_Packed) can be received
|
|
using the type MPI_Packed. Such a message can then be unpacked by calls
|
|
to \fI\%MPI_Unpack\fP\&.
|
|
.sp
|
|
A packing unit (or a message created by a regular, “typed” send) can be
|
|
unpacked into several successive messages. This is effected by several
|
|
successive related calls to \fI\%MPI_Unpack\fP, where the first call provides
|
|
position = 0, and each successive call inputs the value of position that
|
|
was output by the previous call, and the same values for inbuf, insize,
|
|
and comm.
|
|
.sp
|
|
The concatenation of two packing units is not necessarily a packing
|
|
unit; nor is a substring of a packing unit necessarily a packing unit.
|
|
Thus, one cannot concatenate two packing units and then unpack the
|
|
result as one packing unit; nor can one unpack a substring of a packing
|
|
unit as a separate packing unit. Each packing unit that was created by a
|
|
related sequence of pack calls or by a regular send must be unpacked as
|
|
a unit, by a sequence of related unpack calls.
|
|
.SH ERRORS
|
|
.sp
|
|
Almost all MPI routines return an error value; C routines as the return result
|
|
of the function and Fortran routines in the last argument.
|
|
.sp
|
|
Before the error value is returned, the current MPI error handler associated
|
|
with the communication object (e.g., communicator, window, file) is called.
|
|
If no communication object is associated with the MPI call, then the call is
|
|
considered attached to MPI_COMM_SELF and will call the associated MPI error
|
|
handler. When MPI_COMM_SELF is not initialized (i.e., before
|
|
\fI\%MPI_Init\fP/\fI\%MPI_Init_thread\fP, after \fI\%MPI_Finalize\fP, or when using the Sessions
|
|
Model exclusively) the error raises the initial error handler. The initial
|
|
error handler can be changed by calling \fI\%MPI_Comm_set_errhandler\fP on
|
|
MPI_COMM_SELF when using the World model, or the mpi_initial_errhandler CLI
|
|
argument to mpiexec or info key to \fI\%MPI_Comm_spawn\fP/\fI\%MPI_Comm_spawn_multiple\fP\&.
|
|
If no other appropriate error handler has been set, then the MPI_ERRORS_RETURN
|
|
error handler is called for MPI I/O functions and the MPI_ERRORS_ABORT error
|
|
handler is called for all other MPI functions.
|
|
.sp
|
|
Open MPI includes three predefined error handlers that can be used:
|
|
.INDENT 0.0
|
|
.IP \(bu 2
|
|
\fBMPI_ERRORS_ARE_FATAL\fP
|
|
Causes the program to abort all connected MPI processes.
|
|
.IP \(bu 2
|
|
\fBMPI_ERRORS_ABORT\fP
|
|
An error handler that can be invoked on a communicator,
|
|
window, file, or session. When called on a communicator, it
|
|
acts as if \fI\%MPI_Abort\fP was called on that communicator. If
|
|
called on a window or file, acts as if \fI\%MPI_Abort\fP was called
|
|
on a communicator containing the group of processes in the
|
|
corresponding window or file. If called on a session,
|
|
aborts only the local process.
|
|
.IP \(bu 2
|
|
\fBMPI_ERRORS_RETURN\fP
|
|
Returns an error code to the application.
|
|
.UNINDENT
|
|
.sp
|
|
MPI applications can also implement their own error handlers by calling:
|
|
.INDENT 0.0
|
|
.IP \(bu 2
|
|
\fI\%MPI_Comm_create_errhandler\fP then \fI\%MPI_Comm_set_errhandler\fP
|
|
.IP \(bu 2
|
|
\fI\%MPI_File_create_errhandler\fP then \fI\%MPI_File_set_errhandler\fP
|
|
.IP \(bu 2
|
|
\fI\%MPI_Session_create_errhandler\fP then \fI\%MPI_Session_set_errhandler\fP or at \fI\%MPI_Session_init\fP
|
|
.IP \(bu 2
|
|
\fI\%MPI_Win_create_errhandler\fP then \fI\%MPI_Win_set_errhandler\fP
|
|
.UNINDENT
|
|
.sp
|
|
Note that MPI does not guarantee that an MPI program can continue past
|
|
an error.
|
|
.sp
|
|
See the \fI\%MPI man page\fP for a full list of \fI\%MPI error codes\fP\&.
|
|
.sp
|
|
See the Error Handling section of the MPI\-3.1 standard for
|
|
more information.
|
|
.sp
|
|
\fBSEE ALSO:\fP
|
|
.INDENT 0.0
|
|
.INDENT 3.5
|
|
.INDENT 0.0
|
|
.IP \(bu 2
|
|
\fI\%MPI_Pack\fP
|
|
.IP \(bu 2
|
|
\fI\%MPI_Pack_size\fP
|
|
.UNINDENT
|
|
.UNINDENT
|
|
.UNINDENT
|
|
.SH COPYRIGHT
|
|
2003-2025, The Open MPI Community
|
|
.\" Generated by docutils manpage writer.
|
|
.
|