PKMESG(3PVM)

💌 PKMESG — packing messages inside messages, bestie 💌

okay so this is PKMESG(3PVM) from PVM Version 3.4, and it's literally the "message-ception" page. we're putting whole messages inside other messages. no cap. 🫶

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✨ NAME ✨

pvm_pkmesg, pvm_pkmesgbody, pvm_upkmesg — pack messages into other messages. yes the whole vibe is nesting. it's giving russian dolls but make it IPC. 🪆

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🌸 SYNOPSIS 🌸

C besties:

int info = pvm_pkmesg( int bufid )
int info = pvm_pkmesgbody( int bufid )
int newbufid = pvm_upkmesg( )

Fortran besties:

call pvmfpkmesg( bufid, info )
call pvmfpkmesgbody( bufid, info )
call pvmfupkmesg( bufid, newbufid )

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🎀 PARAMETERS 🎀

• bufid — the message buffer you're packing. the little guy going into the envelope 💖
• newbufid — either the new message buffer that got unpacked, or a result code. it's doing double duty, she contains multitudes ✨
• info — result code. the receipts. 🧾

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👑 DESCRIPTION 👑

so these functions exist so you can shove entire messages into other messages, treating them like they're just another data element. iconic behavior honestly.

pvm_pkmesg packs the specified message into the current send buffer. and not just the body — the entire body plus all the header attributes go in:

• length
• context tag
• message tag
• wait identifier
• encoding
• checksum
• source and destination addresses

🚨 okay important: the buffer you specify must not be the same as the current send buffer. like, do not do that. that's the rule.

the slay part: you can pack multiple messages into a single message, and packed messages can be mixed with any other data types. go off, truly. 🔥

pvm_upkmesg unpacks a message from the current receive buffer, and it allocates a new message buffer for it. the body of the newly created message, plus all those header attributes listed above, match the one you originally packed with pvm_pkmesg. so it comes out looking exactly like it went in. periodt. 💅

pvm_pkmesgbody is like pvm_pkmesg's chill sibling — it packs only the body of the specified message and omits the header fields. in other words, it splices the messages together, and the included message is left unaltered. untouched. pristine. 🦋

⚠️ but listen: when you call pvm_pkmesgbody, the encoding types of the two messages must match, because the included message body is simply appended to the send buffer. no matching encoding = no vibes. also, calls to pvm_pkmesgbody can be mixed with calls to pack any other data types. flexible queen.

📌 Note: pvm_upkmesgbody doesn't exist, because PVM doesn't keep track of the boundary between the two messages. she simply cannot tell where one ends and the other begins 😭 so don't go looking for it, bestie.

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🌈 EXAMPLES 🌈

pvm_recv(-1, -1);
pvm_initsend(PvmDataDefault);
pvm_pkstr("here is the message I received...");
pvm_pkmesg(pvm_getrbuf());

look at that. received a message, started a new send buffer, packed a string, then packed the entire received message in after it. main character energy fr fr. 🌟

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💀 ERRORS 💀

the following error conditions can be returned by pvm_pkmesg, pvm_pkmesgbody or pvm_upkmesg:

• PvmBadParam — an invalid value was specified for the bufid argument, or bufid is the current send buffer. (yeah, that thing we told you not to do.)
• PvmNoSuchBuf — message buffer bufid doesn't exist. she's not here. 🙈
• PvmNoMem — Libpvm is unable to allocate memory to pack data. out of room, no space, the vibe is cramped.
• PvmNoData — the end of the message has been reached, perhaps because pack and unpack calls were mismatched. you zigged when you should have zagged 😭
• PvmNoBuf — there is no current send (or receive) buffer. nothing to work with. empty.
• PvmMismatch — pvm_pkmesgbody was called and the encoding types of bufid and the current send buffer don't match. told you the encodings had to match!! ⚠️

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🦋 SEE ALSO 🦋

• pvm_getrbuf(3PVM)
• pvm_getsbuf(3PVM)
• pvm_pack(3PVM)

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and that's the whole page, bestie. mwah. 💜

this was PVM Version 3.4, dated 10 February, 1995 — yes she's vintage, yes she still ate, and no we will not be discussing how old that makes her. 🎀✨