194 строки
6.4 KiB
Groff
194 строки
6.4 KiB
Groff
.\"Copyright 2006, Sun Microsystems, Inc. All rights reserved. Use is subject to license terms.
|
|
.\" Copyright (c) 1996 Thinking Machines Corporation
|
|
.TH MPI_Pack_external 3OpenMPI "September 2006" "Open MPI 1.2" " "
|
|
|
|
.SH NAME
|
|
\fBMPI_Pack_external\fP \- Writes data to a portable format
|
|
|
|
.SH SYNTAX
|
|
.ft R
|
|
|
|
.SH C Syntax
|
|
.nf
|
|
#include <mpi.h>
|
|
int MPI_Pack_external(char *\fIdatarep\fP, void *\fIinbuf\fP,
|
|
int \fIincount\fP, MPI_Datatype\fI datatype\fP,
|
|
void *\fIoutbuf\fP, MPI_Aint \fIoutsize\fP,
|
|
MPI_Aint *\fIposition\fP)
|
|
|
|
.SH Fortran Syntax
|
|
.nf
|
|
INCLUDE 'mpif.h'
|
|
MPI_PACK_EXTERNAL(\fIDATAREP, INBUF, INCOUNT, DATATYPE,
|
|
OUTBUF, OUTSIZE, POSITION, IERROR\fP)
|
|
|
|
INTEGER \fIINCOUNT, DATATYPE, IERROR\fP
|
|
INTEGER (KIND=MPI_ADDRESS_KIND) \fIOUTSIZE, POSITION\fP
|
|
CHARACTER*(*) \fIDATAREP\fP
|
|
<type> \fIINBUF(*), OUTBUF(*)\fP
|
|
|
|
.SH C++ Syntax
|
|
.nf
|
|
#include <mpi.h>
|
|
void MPI::Datatype::Pack_external(const char* \fIdatarep\fP,
|
|
const void* \fIinbuf\fP, int \fIincount\fP,
|
|
void* \fIoutbuf\fP, MPI::Aint \fIoutsize\fP,
|
|
MPI::Aint& \fIposition\fP) const
|
|
|
|
.SH INPUT PARAMETERS
|
|
.ft R
|
|
.TP 1i
|
|
datarep
|
|
Data representation (string).
|
|
.ft R
|
|
.TP 1i
|
|
inbuf
|
|
Input buffer start (choice).
|
|
.TP 1i
|
|
incount
|
|
Number of input data items (integer).
|
|
.TP 1i
|
|
datatype
|
|
Datatype of each input data item (handle).
|
|
.TP 1i
|
|
outsize
|
|
Output buffer size, in bytes (integer).
|
|
|
|
.SH INPUT/OUTPUT PARAMETER
|
|
.ft R
|
|
.TP 1i
|
|
position
|
|
Current position in buffer, in bytes (integer).
|
|
|
|
.SH OUTPUT PARAMETERS
|
|
.ft R
|
|
.TP 1i
|
|
outbuf
|
|
Output buffer start (choice).
|
|
.TP 1i
|
|
IERROR
|
|
Fortran only: Error status (integer).
|
|
|
|
.SH DESCRIPTION
|
|
.ft R
|
|
MPI_Pack_external packs data into the external32 format, a universal
|
|
data representation defined by the MPI Forum. This format is useful
|
|
for exchanging data between MPI implementations, or when writing data
|
|
to a file.
|
|
.sp
|
|
The input buffer is specified by \fIinbuf\fP, \fIincount\fP and
|
|
\fIdatatype\fP, and may be any communication buffer allowed in
|
|
MPI_Send. The output buffer \fIoutbuf\fP must be a contiguous storage
|
|
area containing \fIoutsize\fP bytes.
|
|
.sp
|
|
The input value of \fIposition\fP is the first position in
|
|
\fIoutbuf\fP to be used for packing (measured in bytes, not elements,
|
|
relative to the start of the buffer). When the function returns,
|
|
\fIposition\fP is incremented by the size of the packed message, so
|
|
that it points to the first location in \fIoutbuf\fP following the
|
|
packed message. This way it may be used as input to a subsequent call
|
|
to MPI_Pack_external.
|
|
.sp
|
|
|
|
\fBExample:\fP An example using MPI_Pack_external:
|
|
.sp
|
|
.nf
|
|
int position, i;
|
|
double msg[5];
|
|
char buf[1000];
|
|
|
|
\&...
|
|
|
|
MPI_Comm_rank(MPI_COMM_WORLD, &myrank);
|
|
if (myrank == 0) { /* SENDER CODE */
|
|
position = 0;
|
|
i = 5; /* number of doubles in msg[] */
|
|
MPI_Pack_external("external32", &i, 1, MPI_INT,
|
|
buf, 1000, &position);
|
|
MPI_Pack_external("external32", &msg, i, MPI_DOUBLE,
|
|
buf, 1000, &position);
|
|
MPI_Send(buf, position, MPI_PACKED, 1, 0,
|
|
MPI_COMM_WORLD);
|
|
} else { /* RECEIVER CODE */
|
|
MPI_Recv(buf, 1, MPI_PACKED, 0, 0, MPI_COMM_WORLD,
|
|
MPI_STATUS_IGNORE);
|
|
MPI_Unpack_external("external32", buf, 1000,
|
|
MPI_INT, &i, 1, &position);
|
|
MPI_Unpack_external("external32", buf, 1000,
|
|
MPI_DOUBLE, &msg, i, &position);
|
|
}
|
|
|
|
.SH NOTES
|
|
.ft R
|
|
The \fIdatarep\fP argument specifies the data format. The only valid
|
|
value in the current version of MPI is "external32". The argument is
|
|
provided for future extensibility.
|
|
.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
|
|
MPI_Pack_external, where the first call provides \fIposition\fP=0,
|
|
and each successive call inputs the value of \fIposition\fP that was
|
|
output by the previous call, along with the same values for
|
|
\fIoutbuf\fP and \fIoutcount\fP. 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 packing unit can be unpacked into several successive messages. This
|
|
is effected by several successive related calls to
|
|
MPI_Unpack_external, where the first call provides \fIposition\fP=0,
|
|
and each successive call inputs the value of position that was output
|
|
by the previous call, and the same values for \fIinbuf\fP and
|
|
\fIinsize\fP.
|
|
.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 must be unpacked as a unit
|
|
by a sequence of related unpack calls.
|
|
|
|
.SH ERRORS
|
|
.ft R
|
|
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.
|
|
.sp
|
|
Before the error value is returned, the current MPI error handler is
|
|
called. By default, this error handler aborts the MPI job, except for
|
|
I/O function errors. The error handler may be changed with
|
|
MPI_Comm_set_errhandler; the predefined error handler MPI_ERRORS_RETURN
|
|
may be used to cause error values to be returned. Note that MPI does not
|
|
guarantee that an MPI program can continue past an error.
|
|
.sp
|
|
See the MPI man page for a full list of MPI error codes.
|
|
|
|
.SH SEE ALSO
|
|
.ft R
|
|
.nf
|
|
MPI_Pack_external_size
|
|
MPI_Send
|
|
MPI_Unpack_external
|
|
sscanf(3C)
|
|
|
|
' @(#)MPI_Pack_external.3 1.6 06/03/09
|