PACK(3PVM)

📦 version 3.4.6, in debian bookworm, ubuntu jammy

PACK(3PVM) 💖

okay bestie, gather round, because this is the packing page and it's literally the moment your data gets its little suitcase packed for the trip across the cluster. this is from PVM Version 3.4, so it's vintage but it ate. 🧳✨

✨ NAME ✨

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

no cap, that's the whole job description. 💅

🌸 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 who's who in the group chat:

  • fmt — a printf-like format expression specifying what to pack. (see the discussion below, it's giving very BNF.)
  • nitem — the total number of items to be packed. NOT the number of bytes, bestie, don't get it twisted. 🙈
  • stride — the stride used when packing the items. like, for example, if stride = 2 in pvm_pkcplx, then every other complex number gets packed. skipping through the array like 💃
  • xp — pointer to the beginning of a block of bytes. can be any data type, but it must match the corresponding unpack data type.
  • 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. the options are:
    • 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. negative = bad vibes. 💀

🦋 DESCRIPTION 🦋

so 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.

one exception to the whole thing, and it's the icon herself: pvm_pkstr(), which by definition packs a NULL terminated character string and thus does not need nitem or stride arguments. 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 — this is 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. that's the rule. 🚫

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. yes bestie, even a lone lil variable gets its moment. ⭐

the pvm_packf() of it all

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)
'*' 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 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.

the unpacking rules (do not break these) 😭

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 chaotic and it will not work. periodt.

🔥 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.

like... it's just not gonna happen, bestie. the implementation said no. 💀

💀 ERRORS 💀

  • PvmNoMem — malloc has failed. 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 message.
  • 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)

okay that's the whole page, you absolutely ate that reading bestie 🫶 this was PVM Version 3.4, page PACK(3PVM), dated 30 August, 1993 — iconic behavior honestly, go pack something. 💖🌸🦋✨

📦 where this page comes from