PACK(3PVM)

📦 version 3.4.6, in debian bookworm, ubuntu jammy

🎀 NAME 🎀

pvm_pack — pack the active message buffer with arrays of prescribed data type. 💖

okay so this is the PACK page from PVM Version 3.4 (that's PACK(3PVM) if you're keeping receipts), and honestly? it's the pre-send glow-up station. you got data, you got a message buffer, and bestie, we're packing it. ✨

✨ 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 🌸

  • fmt — a printf-like format expression telling PVM what to pack. (there's a whole discussion below, don't skip it 💀)
  • nitem — the total number of items to be packed. not bytes, bestie, ITEMS. the way that matters 😭
  • stride — the stride used when packing the items. so like, if stride = 2 in pvm_pkcplx, then every other complex number gets packed. skips a beat, iconic.
  • 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 cap.
  • 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 — an integer specifying the type of data being packed. here's the menu, hun:
    • STRING — 0
    • BYTE1 — 1
    • INTEGER2 — 2
    • INTEGER4 — 3
    • REAL4 — 4
    • COMPLEX8 — 5
    • REAL8 — 6
    • COMPLEX16 — 7
  • info — integer status code the routine hands back. anything less than zero means something went wrong. 🙈

💖 DESCRIPTION 💖

so, every single one of the pvm_pk* routines packs an array of the given data type straight into the active send buffer. the arguments for each routine are: a pointer to the first item to pack, nitem (the total number of items to pack from this array), and stride (the stride to use while packing). that's it. that's the whole vibe. ✨

the one exception is pvm_pkstr(), which by definition packs a NULL terminated character string and therefore does not need nitem or stride arguments. meanwhile the Fortran routine pvmfpack( STRING, ... ) wants nitem to be the number of characters in the string, and stride to be 1. periodt.

you can pack a null string ("") — that's just a string with no characters before the terminating '\0'. 🎀 however, packing a null string pointer, (char *)0, is not allowed. don't do it, bestie, it's not the move.

if the packing works out, info will be 0. if some error shows up, info will be < 0. simple as.

and yeah — you can pack a single variable (not an array) by setting nitem = 1 and stride = 1. main character energy for one lil value. 👑

🦋 the pvm_packf() format thing 🦋

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. here's the BNF-like description of the format syntax, verbatim, no edits:

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, decoded for you:

  • + means initsend — must match an int (how) in the param list.
  • c packs/unpacks 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. 🌟

🔥 future tea 🔥

future extensions to the what argument in pvmfpack will include 64 bit types once 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. and 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. slay.

💀 the golden rule 💀

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. and packing 10 integers and 100 floats then trying to unpack only 3 integers and the 100 floats will also fail. like, the math isn't mathing. don't do it.

🌈 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. that's the vibe check failing, fr fr. 🫶

😭 ERRORS 😭

  • PvmNoMem — Malloc has failed. the message buffer size has exceeded the available memory on this host. 💀
  • PvmNoBuf — there is no active send buffer to pack into. try calling pvm_initsend before packing the message. bestie, you gotta have somewhere to put it.
  • 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's giving too much. 😭

🌸 SEE ALSO 🌸

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

and that's the whole page, babe — brought to you by PVM Version 3.4, dated 30 August, 1993. yes, 1993. she's vintage, she's iconic, and she still packs. 💅✨🎀💖🦋

📦 where this page comes from