PACK(3PVM)

📦 version 3.4.6, in debian bookworm, ubuntu jammy

💖 PACK(3PVM) 💖

okay so bestie, welcome to pvm_pack — the glow-up era where your data gets ✨packed✨ into the active message buffer. This is from PVM Version 3.4, and it's giving "my arrays are going on a trip and they need to be seated properly." Buckle in, we're doing this together. 🎀

✨ NAME ✨

pvm_pack — pack the active message buffer with arrays of prescribed data type. no cap, that's the whole job. 💅

🌸 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. (There's a whole discussion on this later, keep scrolling bestie.)
  • nitem — the total number of items to be packed. Items, not bytes! Do not come for me with bytes. 🙈
  • stride — the stride used when packing the items. Like, if stride = 2 in pvm_pkcplx, then every other complex number gets packed. Skipping queen behavior. ✨
  • xp — pointer to the beginning of a block of bytes. Can be any data type, but it has to match the corresponding unpack data type. Matching is not optional, it's the vibe check. 💀
  • 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, bestie:
    • 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 mean error. Negative = bad. Periodt. 😭

💜 DESCRIPTION 💜

Every single one 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. Simple. Iconic. 🫶

The exception is pvm_pkstr() — it packs a NULL terminated character string by definition, so it does not need nitem or stride arguments. Meanwhile the Fortran routine pvmfpack( STRING, ... ) expects nitem to be the number of characters in the string and stride to be 1. Different rules for different routines, iykyk. ✨

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. Do not do it. Not even once. 💀

If the packing is successful, info will be 0. If some error occurs then info will be < 0. That's the whole mood. 🌈

A single variable (not an array) can be packed by setting nitem = 1 and stride = 1. Baby steps, bestie, we love a solo pack. 💖

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 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 and then trying to unpack only 3 integers and the 100 floats will also fail. Symmetry is the moment. Break it and it breaks you. 💅

🎀 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 you, bestie, it's the implementation. 😭

💀 ERRORS 💀

  • PvmNoMem — Malloc has failed. Message buffer size has exceeded the available memory on this host. The host said "I'm full." 🍓
  • PvmNoBuf — there is no active send buffer to pack into. Try calling pvm_initsend before packing message. You gotta open the bag before you put stuff in 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. The value did not fit and it's giving overflow. 💀

🌟 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 PVM Version 3.4, dated 30 August, 1993 — PACK(3PVM), signing off. go pack something iconic. 👑✨🦋

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