UNPACK(3PVM)

💌 NAME

pvm_unpack — unpack the active message buffer into arrays of prescribed data type. bestie, this is where the data you sent finally gets out of the buffer and into your actual variables 🫶

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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 )

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🎀 PARAMETERS

• fmt — a printf-like format expression that says what to pack. (there's a whole discussion below, keep scrolling 💅)
• nitem — the total number of items to be unpacked (not the number of bytes, okay? don't get it twisted 🙈).
• stride — the stride used when packing the items. like, if stride = 2 in pvm_upkcplx, then every other complex number gets unpacked. every other. iconic behavior honestly.
• xp — pointer to the beginning of a block of bytes. can be any data type, but it must match the corresponding pack data type. no mixing, babe.
• 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:

     what options
STRING         0    REAL4          4
BYTE1          1    COMPLEX8       5
INTEGER2       2    REAL8          6
INTEGER4       3    COMPLEX16      7

• info — integer status code returned by the routine. values less than zero indicate an error 😭

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💖 DESCRIPTION

okay so, each of the pvm_upk* routines unpacks an array of the given data type from the active receive buffer. the arguments for each routine are: a pointer to the array you're unpacking into, nitem which is the total number of items to unpack, and stride which is the stride to use when unpacking. slay.

the one exception is pvm_upkstr(), which by definition unpacks a NULL terminated character string, so it doesn't need nitem or stride arguments at all — she's low maintenance 💅. 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. that's it, that's the vibe check.

a single variable (not an array) can be unpacked by setting nitem = 1 and stride = 1. main character energy for one little value ✨

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 (yes, addresses, don't forget the &). 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. periodt.

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. so like… know your bytes, bestie 😭

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. it's giving consequences. 🙈

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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 )

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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. girl you reached into the void 🫠
• 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).
• PvmNoBuf — there is no active receive buffer to unpack. nothing to unpack, bestie, the buffer is empty 💀

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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, no cap 💜 this was PVM Version 3.4, dated 30 August, 1993 — yes she's vintage, yes she still ate. go unpack something gorgeous 🎀✨