UNPACK(3PVM)

UNPACK(3PVM) 💖

okay bestie, welcome to PVM Version 3.4 and specifically to the page about pvm_unpack, the part of the group chat where you finally open the messages somebody sent you. we're in section 3PVM, and no cap, this one is important — packing without unpacking is giving "texted you my whole heart and you left it on read" 💀

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✨ NAME ✨

pvm_unpack — Unpack the active message buffer into arrays of prescribed data type.

like, you got a buffer full of vibes and you're pouring them back into your actual variables. main character behavior 🫶

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🎀 SYNOPSIS 🎀

C

int info = pvm_unpackf( const char *fmt, ... )
int info = pvm_upkbyte( char *xp, int nitem, int stride)
int info = pvm_upkcplx( float *cp, int nitem, int stride)
int info = pvm_upkdcplx( double *zp, int nitem, int stride)
int info = pvm_upkdouble( double *dp, int nitem, int stride)
int info = pvm_upkfloat( float *fp, int nitem, int stride)
int info = pvm_upkint( int *ip, int nitem, int stride)
int info = pvm_upkuint( unsigned int *ip, int nitem, int stride )
int info = pvm_upkushort( unsigned short *ip, int nitem, int stride )
int info = pvm_upkulong( unsigned long *ip, int nitem, int stride )
int info = pvm_upklong( long *ip, int nitem, int stride)
int info = pvm_upkshort( short *jp, int nitem, int stride)
int info = pvm_upkstr( char *sp )

Fortran

call pvmfunpack( what, xp, nitem, stride, info )

that's twelve whole C routines plus one Fortran baddie. twelve. she contains multitudes 💅

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🌸 PARAMETERS 🌸

• fmt — a printf-like format expression specifying what to pack. (there's a whole discussion below, don't skip it, i know you want to)
• nitem — the total number of items to be unpacked. not bytes. items. we're counting items here, not vibes ✨
• stride — the stride to be used when packing the items. like, for example, if stride = 2 in pvm_upkcplx, then every other complex number will be unpacked. every. other. one. 🦋
• xp — pointer to the beginning of a block of bytes. can be any data type, but it must match the corresponding pack data type. match. them. up.
• cp — complex array at least nitem*stride items long.
• zp — double precision complex array at least nitem*stride items long.
• dp — double precision real array at least nitem*stride items long.
• fp — real array at least nitem*stride items long.
• ip — integer array at least nitem*stride items long.
• jp — Integer*2 array at least nitem*stride items long.
• sp — pointer to a null terminated character string.
• what — integer specifying the type of data being unpacked. the options are:

🧚 the what options 🧚

• STRING — 0
• BYTE1 — 1
• INTEGER2 — 2
• INTEGER4 — 3
• REAL4 — 4
• COMPLEX8 — 5
• REAL8 — 6
• COMPLEX16 — 7
• info — integer status code returned by the routine. values less than zero indicate an error. zero is the slay outcome, negative is the "we need to talk" outcome 😭

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💜 DESCRIPTION 💜

Each of the pvm_upk* routines unpacks an array of the given data type from the active receive buffer. The arguments for each of the routines are a pointer to the array to be unpacked into, nitem which is the total number of items to unpack, and stride which is the stride to use when unpacking.

An exception is pvm_upkstr() which by definition unpacks a NULL terminated character string and thus does not need nitem or stride arguments. The Fortran routine pvmfunpack( STRING, ... ) expects nitem to be the number of characters in the string and stride to be 1.

If the unpacking is successful, info will be 0. If some error occurs then info will be < 0.

A single variable (not an array) can be unpacked by setting nitem = 1 and stride = 1. one item, one stride, one little moment of peace 🎀

The routine pvm_unpackf() uses a printf-like format expression to specify what and how to unpack data from the receive buffer. All variables are passed as addresses. A BNF-like description of the format syntax is:

format : null | init | format fmt
init : null | '%' '+'
fmt : '%' count stride modifiers fchar
fchar : 'c' | 'd' | 'f' | 'x' | 's'
count : null | [0-9]+ | '*'
stride : null | '.' ( [0-9]+ | '*' )
modifiers : null | modifiers mchar
mchar : 'h' | 'l' | 'u'

Formats:

• + means initsend — must match an int (how) in the param list.
• c — pack/unpack bytes
• d — integer
• f — float
• x — complex float
• s — string

Modifiers:

• h — short (int)
• l — long (int, float, complex float)
• u — unsigned (int)

'*' count or stride must match an int in the param list. like, the asterisk is not free, she needs a plus-one 🌟

Future extensions to the what argument in pvmfunpack will include 64 bit types when XDR encoding of these types is available. Meanwhile users should be aware that precision can be lost when passing data from a 64 bit machine like a Cray to a 32 bit machine like a SPARCstation. As a mnemonic the what argument name includes the number of bytes of precision to expect. By setting encoding to PVMRAW (see pvmfinitsend) data can be transferred between two 64 bit machines with full precision even if the PVM configuration is heterogeneous.

Messages should be unpacked exactly like they were packed to insure data integrity. Packing integers and unpacking them as floats will often fail because a type encoding will have occurred transferring the data between heterogeneous hosts. Packing 10 integers and 100 floats then trying to unpack only 3 integers and the 100 floats will also fail. 💀

fr fr: unpack it the way you packed it. no freestyling. the buffer is not a build-your-own-adventure, bestie.

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🌈 EXAMPLES 🌈

C:

info = pvm_recv( tid, msgtag );
info = pvm_upkstr( string );
info = pvm_upkint( &size, 1, 1 );
info = pvm_upkint( array, size, 1 );
info = pvm_upkdouble( matrix, size*size, 1 );

int count, *iarry;
double darry[4];
   pvm_unpackf("%d", &count);
   pvm_unpackf("%*d %4lf", count, iarry, darry);

Fortran:

CALL PVMFRECV( TID, MSGTAG, INFO );
CALL PVMFUNPACK( INTEGER4, NSIZE, 1, 1, INFO )
CALL PVMFUNPACK( STRING, STEPNAME, 8, 1, INFO )
CALL PVMFUNPACK( REAL4, A(5,1), NSIZE, NSIZE , INFO )

see how "%*d %4lf" pulls the count from the param list? that's the '*' doing her little thing. iconic 👑

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🍓 ERRORS 🍓

• PvmNoData — Reading beyond the end of the receive buffer. Most likely cause is trying to unpack more items than were originally packed into the buffer. you're reaching into the bag for snacks that were never there 😭
• PvmBadMsg — The received message can not be decoded. Most likely because the hosts are heterogeneous and the user specified an incompatible encoding. Try setting the encoding to PvmDataDefault (see pvm_mkbuf). she's speaking a language you don't have installed 🙈
• PvmNoBuf — There is no active receive buffer to unpack. literally nothing to open. empty inbox energy 💀

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🔥 SEE ALSO 🔥

• pvm_pack(3PVM)
• pvm_send(3PVM)
• pvm_recv(3PVM)
• pvm_pkmesg(3PVM)

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and that's the whole page, bestie. pack responsibly, unpack exactly what you packed, and never ever guess at a stride ✨

that was PVM Version 3.4, page UNPACK(3PVM), dated 30 August, 1993 — yes she's a vintage icon and yes she still eats 💅🌸