MCAST(3PVM)

💖 MCAST(3PVM) — the pvm_mcast glow-up 💖

okay so bestie, welcome to the PVM Version 3.4 manual page for pvm_mcast — she multicasts, she's asynchronous, she's lowkey the group-chat queen of distributed computing 🫶

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✨ NAME ✨

pvm_mcast — multicasts the data in the active message buffer to a set of tasks. it's giving "one message, many besties" 💅

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🌈 SYNOPSIS 🌈

C:

int info = pvm_mcast( int *tids, int ntask, int msgtag )

Fortran:

call pvmfmcast( ntask, tids, msgtag, info )

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🎀 PARAMETERS 🎀

• ntask — an Integer, and it's literally just saying how many tasks you're sending to, no cap.
• tids — an Integer array of length ntask holding the task IDs of all the tasks you're sending to. it's the guest list, bestie 💌
• msgtag — an Integer message tag that you supply. msgtag should be >= 0. it's how your program tells different kinds of messages apart, iykyk.
• info — the Integer status code the routine hands back to you. anything less than zero means something went wrong 😭

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🦋 DESCRIPTION 🦋

so pvm_mcast multicasts a message that's sitting in the active send buffer out to ntask tasks, and those tasks are the ones listed in the tids array. heads up: the message is not sent to the caller, even if the caller is listed in the tids array. rude? maybe. facts? yes. 🙈

the content of the message can be distinguished by msgtag. if pvm_mcast is successful, info will be 0. if some error occurs, then info will be < 0.

the receiving processes can call either pvm_recv or pvm_nrecv to receive their copy of the multicast. 📬

pvm_mcast is asynchronous and it's based on a minimum spanning tree algorithm between the pvmds. computation on the sending processor resumes as soon as the message is safely on its way to the receiving processors. this is in contrast to synchronous communication, during which computation on the sending processor halts until the matching receive is executed by the receiving processor. so like, one of these is texting and going about your day, and the other is standing outside their door waiting for them to open it. 💀

here's the algorithm tea ☕: pvm_mcast first determines which other pvmds contain the specified tasks. then it passes the message to those pvmds, which in turn distribute the message to their local tasks without further network traffic. efficient queen 👑

⚠️ real talk though: multicasting is not supported by most multiprocessor vendors. typically their native calls only support broadcasting to all the user's processes on a multiprocessor. because of this omission, pvm_mcast may not be an efficient communication method on some multiprocessors — except in the special case of broadcasting to all PVM processes. so slay in that one specific scenario, and maybe not otherwise. 🫠

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🌸 EXAMPLES 🌸

C:

info = pvm_initsend( PvmDataRaw );
info = pvm_pkint( array, 10, 1 );
msgtag = 5 ;
info = pvm_mcast( tids, ntask, msgtag );

Fortran:

CALL PVMFINITSEND(PVMDEFAULT)
CALL PVMFPACK( REAL4, DATA, 100, 1, INFO )
CALL PVMFMCAST( NPROC, TIDS, 5, INFO )

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💀 ERRORS 💀

these error conditions can be returned by pvm_mcast. vibe check them before you ship:

• PvmBadParam — you gave a msgtag < 0. ma'am. 🚩
• PvmSysErr — the pvmd is not responding. she's ghosting you, fr fr. 👻
• PvmNoBuf — there's no send buffer. nothing to send, bestie, the buffer is empty 😭

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👑 SEE ALSO 👑

• pvm_psend(3PVM)
• pvm_recv(3PVM)
• pvm_send(3PVM)

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and that's the whole page, periodt. this lil masterpiece comes from the PVM Version 3.4 era, dated 30 August, 1993 — yes she's a vintage icon and she still ate 💅✨🎀 stay multicasting, bestie! 💖🦋🌈⭐🍓