UNPACK(3PVM)

💖 UNPACK — a.k.a. pvm_unpack 💖

Welcome to the PVM Version 3.4 page for UNPACK(3PVM), bestie. This is where your active message buffer finally gives up the goods and hands you back actual arrays of the data type you asked for. 🎀

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✨ NAME ✨

pvm_unpack — unpack the active message buffer into arrays of prescribed data type. It's giving "you packed it, now you unpack it, no cap." 💅

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🌸 SYNOPSIS 🌸

C

int info = pvm_unpackf( const char *fmt, ... )
int info = pvm_upkbyte( char *xp, int nitem, int stride)
int info = pvm_upkcplx( float *cp, int nitem, int stride)
int info = pvm_upkdcplx( double *zp, int nitem, int stride)
int info = pvm_upkdouble( double *dp, int nitem, int stride)
int info = pvm_upkfloat( float *fp, int nitem, int stride)
int info = pvm_upkint( int *ip, int nitem, int stride)
int info = pvm_upkuint( unsigned int *ip, int nitem, int stride )
int info = pvm_upkushort( unsigned short *ip, int nitem, int stride )
int info = pvm_upkulong( unsigned long *ip, int nitem, int stride )
int info = pvm_upklong( long *ip, int nitem, int stride)
int info = pvm_upkshort( short *jp, int nitem, int stride)
int info = pvm_upkstr( char *sp )

Fortran

call pvmfunpack( what, xp, nitem, stride, info )

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🦋 PARAMETERS 🦋

• fmt — a printf-like format expression that says what to pack. (More on this below, keep scrolling, it's a whole thing.)
• nitem — the total number of items to be unpacked. Not bytes, bestie, items. Read that twice.
• stride — the stride used when packing the items. So like, if stride = 2 in pvm_upkcplx, then every other complex number gets unpacked. Skipping is the whole vibe. 💫
• xp — pointer to the beginning of a block of bytes. Can be any data type, but it must match the corresponding pack 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 unpacked. Behold, the menu:

👑 what options

• 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. 😭

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🎀 DESCRIPTION 🎀

Each of the pvm_upk* routines unpacks an array of the given data type out of the active receive buffer. For every one of them, the arguments are: a pointer to the array you're unpacking into, nitem which is the total number of items to unpack, and stride which is the stride to use while unpacking. Simple, clean, iconic. ✨

The one exception is pvm_upkstr(), which by definition unpacks a NULL terminated character string, so it literally does not need nitem or stride arguments. Not like other routines. The Fortran routine pvmfunpack( STRING, ... ) does expect nitem to be the number of characters in the string, and stride to be 1.

If the unpacking works out, info will be 0. If something goes wrong, info will be < 0. Vibe check: failed. 💀

A single variable (not an array, just one lil guy) can be unpacked by setting nitem = 1 and stride = 1.

The routine pvm_unpackf() uses a printf-like format expression to specify what to unpack from the receive buffer and how to do it. All variables are passed as addresses. Here's a BNF-like description of the format syntax, in all its glory:

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 — integer
• 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 pvmfunpack 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. No shortcuts, bestie. 😤

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⭐ EXAMPLES ⭐

C:

info = pvm_recv( tid, msgtag );
info = pvm_upkstr( string );
info = pvm_upkint( &size, 1, 1 );
info = pvm_upkint( array, size, 1 );
info = pvm_upkdouble( matrix, size*size, 1 );

int count, *iarry;
double darry[4];
   pvm_unpackf("%d", &count);
   pvm_unpackf("%*d %4lf", count, iarry, darry);

Fortran:

CALL PVMFRECV( TID, MSGTAG, INFO );
CALL PVMFUNPACK( INTEGER4, NSIZE, 1, 1, INFO )
CALL PVMFUNPACK( STRING, STEPNAME, 8, 1, INFO )
CALL PVMFUNPACK( REAL4, A(5,1), NSIZE, NSIZE , INFO )

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💀 ERRORS 💀

• PvmNoData — reading beyond the end of the receive buffer. Most likely cause is trying to unpack more items than were originally packed into the buffer. Bestie, you cannot take out what you never put in.
• PvmBadMsg — the received message can not be decoded. Most likely because the hosts are heterogeneous and the user specified an incompatible encoding. Try setting the encoding to PvmDataDefault (see pvm_mkbuf).
• PvmNoBuf — there is no active receive buffer to unpack. Nothing to unpack. Nothing. 🙈

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👑 SEE ALSO 👑

pvm_pack(3PVM) pvm_send(3PVM), pvm_recv(3PVM), pvm_pkmesg(3PVM)

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Okay that's the whole page, you ate that. 💖 Sending you off with the receipts: this is PVM Version 3.4, and the page is dated 30 August, 1993. Slay, go unpack something responsibly. ✨💅🎀