PACK(3PVM)

💖 PACK(3PVM) 💖

okay bestie, welcome to pvm_pack — the glow-up routine that packs your active message buffer with arrays of prescribed data type. it's giving "loading the dishwasher but the dishwasher is a message buffer and the dishes are your data." periodt. 🌸

this is part of PVM Version 3.4, iykyk.

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✨ 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 )

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🎀 PARAMETERS 🎀

like, every single one, no skips:

• fmt — a printf-like format expression specifying what to pack. (there's a whole discussion, keep reading babe)
• nitem — the total number of items to be packed. not the number of bytes. do not get it twisted. 💅
• stride — the stride to use when packing the items. for example, if stride = 2 in pvm_pkcplx, then every other complex number will be packed. iconic skip-every-other behaviour. 🦋
• xp — pointer to the beginning of a block of bytes. can be any data type, but must match the corresponding unpack data type. no catfishing.
• 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. values less than zero indicate an error. anything < 0 is a bad vibe. 😭

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💜 DESCRIPTION 💜

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.

an exception is 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. nope. not happening. 🙈

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. cute and efficient, we love a shortcut. ✨

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🧚 the pvm_packf() format 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. main character detail, do not forget it.

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. 🌟

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🔮 future tea (the 64-bit situation) 🔮

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. 💅

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🫶 the golden rule of packing & unpacking 🫶

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. match your energies, bestie. the packing and the unpacking have to be in sync or it's over. 💀

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🌈 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 )

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⚠️ 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, the implementation said no. respect it. 😭

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💥 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. (bestie, you forgot to make a buffer. it happens.)
• 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.

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👑 SEE ALSO 👑

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

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and that's the whole page, bestie. this was PVM Version 3.4, dated 30 August, 1993 — yes it's vintage, no we're not over it, she's a classic for a reason. 💖✨🎀🦋🌸💅🫶🔥👑🌈⭐💀🍓🧚💜