PACK(3PVM)

📦 version 3.4.6, in debian bookworm, ubuntu jammy

🌸 NAME 🌸

okay so welcome to PACK(3PVM) — that's page PACK out of the 3PVM manual, and the version we're vibing with is PVM Version 3.4 💖

  • pvm_pack — packs the active message buffer with arrays of a prescribed data type. that's the whole gig bestie, and it ate. 💅

✨ 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 that says what to pack. lowkey the main character of pvm_packf. (there's a whole discussion below, keep scrolling 🫶)
  • nitem — the total number of items to be packed. NOT the number of bytes, bestie, do not get it twisted 😭
  • stride — the stride used when packing the items. so if stride = 2 in pvm_pkcplx, then every other complex number gets packed. skipping through the array like it's got somewhere to be 💅
  • 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 — integer specifying the type of data being packed. here's the menu:
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. anything less than zero means an error happened. 🚨

🦋 DESCRIPTION 🦋

each of the pvm_pk* routines packs an array of the given data type into the active send buffer. the arguments for every one of these routines are:

  1. a pointer to the first item to be packed,
  2. nitem, which is the total number of items to pack from this array, and
  3. stride, which is the stride to use when packing.

the one exception is pvm_pkstr() — by definition it packs a NULL terminated character string, so it simply does not need nitem or stride arguments. iconic, honestly. ✨ and for the Fortran routine pvmfpack( STRING, ... ), it 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 do it. 🙈

if the packing goes well, info will be 0. if some error occurs then info will be < 0.

you can pack a single variable (not an array) by setting nitem = 1 and stride = 1. tiny little pack, adorable. 🎀

the pvm_packf() situation 💅

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.

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)

a ’*' count or stride must match an int in the param list. periodt.

future stuff + precision tea ☕

future extensions to the what argument in pvmfpack will include 64 bit types when XDR encoding of these types is available. meanwhile — and this is important, bestie — 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. slay. 👑

pack it the way you unpack it, fr fr

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. no shortcuts. 💀

🌈 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 a hard no bestie, don't fight it. 😭

💀 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 a message, babe. 🫶
  • 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.

👑 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 one's from PVM Version 3.4, dated 30 August, 1993 — yeah she's vintage, she's iconic, she's still packing buffers. go pack something cute. 🎀✨🦋

📦 where this page comes from