PACK(3PVM)

📦 version 3.4.6, in debian bookworm, ubuntu jammy

💅 NAME 💅

pvm_pack — packs the active message buffer with arrays of a prescribed data type. it's giving data-wrangling main character energy ✨ (this is the PVM Version 3.4 PACK(3PVM) page, bestie, and yes we're doing the whole thing)

🌸 SYNOPSIS 🌸

🎀 C

int info = pvm_packf( const char *fmt, ... )
int info = pvm_pkbyte( char *xp, int nitem, int stride )
int info = pvm_pkcplx( float *cp, int nitem, int stride )
int info = pvm_pkdcplx( double *zp, int nitem, int stride )
int info = pvm_pkdouble( double *dp, int nitem, int stride )
int info = pvm_pkfloat( float *fp, int nitem, int stride )
int info = pvm_pkint( int *ip, int nitem, int stride )
int info = pvm_pkuint( unsigned int *ip, int nitem, int stride )
int info = pvm_pkushort( unsigned short *ip, int nitem, int stride )
int info = pvm_pkulong( unsigned long *ip, int nitem, int stride )
int info = pvm_pklong( long *ip, int nitem, int stride )
int info = pvm_pkshort( short *jp, int nitem, int stride )
int info = pvm_pkstr( char *sp )

🦋 Fortran

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

✨ PARAMETERS ✨

okay so here's the whole cast of characters, no skips 👑

  • fmt — a printf-like format expression that says what to pack. (the deep dive is down below, keep scrolling 🫶)
  • nitem — the total number of items to be packed. not the number of bytes, bestie, items. 💀
  • stride — the stride used when packing the items. like, if stride = 2 in pvm_pkcplx, then every other complex number gets packed. selective packing, we love to see it.
  • xp — pointer to the beginning of a block of bytes. can be any data type, but it must match the corresponding unpack data type. no mismatched vibes allowed.
  • 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 packed. here are the what options, alphabetically served 💁:
    • 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. so like, < 0 = it's not giving 😭

💖 DESCRIPTION 💖

each of the pvm_pk* routines packs an array of the given data type into the active send buffer. the arguments for each of the routines are: a pointer to the first item to be packed, nitem which is the total number of items to pack from this array, and stride which is the stride to use when packing. three little arguments, one big glow-up ✨

the exception: pvm_pkstr(), which by definition packs a NULL terminated character string, and thus does not need nitem or stride arguments. it's built different. the Fortran routine pvmfpack( STRING, ... ) expects nitem to be the number of characters in the string and stride to be 1.

a null string ("") can be packed — that's just a string with no characters before the terminating '\0'. but packing a null string pointer, (char *)0, is not allowed. do not try it, bestie, that's a no. 🙈

if the packing is successful, info will be 0. if some error occurs then info will be < 0.

a single variable (not an array) can be packed by setting nitem = 1 and stride = 1. one item, one stride, one icon 💅

🌈 the pvm_packf() format thing

the routine pvm_packf() uses a printf-like format expression to specify what and how to pack data into the send buffer. all variables are passed as addresses if count and stride are specified — otherwise, variables are assumed to be values. noted. 📝

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 integers
  • 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. don't forget the matching int, or it's over for you fr fr 😭

🔮 the future / precision tea

future extensions to the what argument in pvmfpack 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. symmetric packing/unpacking only, that's the rule. 💀

🍓 EXAMPLES 🍓

C:

info = pvm_initsend( PvmDataDefault );
info = pvm_pkstr( "initial data" );
info = pvm_pkint( &size, 1, 1 );
info = pvm_pkint( array, size, 1 );
info = pvm_pkdouble( matrix, size*size, 1 );
msgtag = 3 ;
info = pvm_send( tid, msgtag );
int count, *iarry;
double darry[4];
pvm_packf("%+ %d %*d %4lf", PvmDataRaw, count, count, iarry, darry);

Fortran:

CALL PVMFINITSEND(PVMRAW, INFO)
CALL PVMFPACK( INTEGER4, NSIZE, 1, 1, INFO )
CALL PVMFPACK( STRING, 'row 5 of NXN matrix', 19, 1, INFO )
CALL PVMFPACK( REAL8, A(5,1), NSIZE, NSIZE , INFO )
CALL PVMFSEND( TID, MSGTAG, INFO )

🧚 WARNINGS 🧚

strings cannot be packed when using the PvmDataInPlace encoding, due to limitations in the implementation. attempting to pack a string using pvm_pkstr or pvm_packf will cause error code PvmNotImpl to be returned. it's not a vibe, it's just how it is 😭

💀 ERRORS 💀

  • PvmNoMem — Malloc has failed. Message buffer size has exceeded the available memory on this host. no memory = no pack, sorry bestie 🫶
  • PvmNoBuf — There is no active send buffer to pack into. try calling pvm_initsend before packing message. yes, actually call it first. 🙈
  • PvmOverflow — Attempt to pack a value too large. e.g. packing an 8-byte long with XDR encoding if the value won't fit into 4 bytes. it simply does not fit, periodt.

👑 SEE ALSO 👑

pvm_initsend(3PVM), pvm_unpack(3PVM), pvm_send(3PVM), pvm_recv(3PVM), pvm_pkmesg(3PVM)

and that's the whole page, bestie!! 🎀 this was the PACK(3PVM) manual page from PVM Version 3.4, dated 30 August, 1993 — yes, 1993, we're literally reading vintage lore and it still slaps. pack responsibly, unpack symmetrically, and stay iconic 💜✨🦋

📦 where this page comes from