PACK(3PVM)

📦 version 3.4.6, in debian bookworm, ubuntu jammy

💖 PACK(3PVM) 💖

okay bestie, listen up, because this one is the vibe of PVM. welcome to PVM Version 3.4, and this is the page for pvm_pack — aka the routine that packs your active message buffer with arrays of prescribed data type. yes, "prescribed". it's giving doctor energy but for bytes. 💅

✨ NAME ✨

pvm_pack — pack the active message buffer with arrays of prescribed data type. no cap, that's literally 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 that says what to pack. (peep the discussion below, it's a whole thing.)
  • nitem — the total number of items to be packed. and bestie, it's items, not the number of bytes. do not get this 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. iconic skipping behavior tbh.
  • xp — pointer to the beginning of a block of bytes. it can be any data type, but it must match the corresponding unpack data type. no mixing, no matching-energy, ok?
  • 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 your what options, laid out all cute:
    • 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 if you see a negative, that's your red flag, bestie. 🚩

🌈 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 routine 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. that's the whole recipe. 💖

the one exception is pvm_pkstr(), which by definition packs a NULL terminated character string and thus does not need nitem or stride arguments. it's the low-maintenance friend of the group. 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 absolutely be packed — it'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. not the move. 🙈

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 little guy. so valid. 🥺

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 then trying to unpack only 3 integers and the 100 floats will also fail. matching energy only, bestie. 💀

🎀 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 will not work. it's not a skill issue, it's a limitation. periodt. 🫶

💀 ERRORS 💀

  • PvmNoMem — malloc has failed. message buffer size has exceeded the available memory on this host. your host said "no thoughts, buffer full". 😭
  • PvmNoBuf — there is no active send buffer to pack into. try calling pvm_initsend before packing message. you forgot to set up the vibe first, bestie.
  • 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, and not in the good way. 🔥

🧚 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 was brought to you by PVM Version 3.4, dated 30 August, 1993 — yes, a vintage icon, ahead of its time, still slaying 💅✨ go pack something. carefully. 🦋💖

📦 where this page comes from