MPIX_Type_iov_len(3)

💖 MPIX_Type_iov_len — the MPI manual, but make it cute 💖

okay bestie, this is the page for MPIX_Type_iov_len, and it lives in section 3 of the MPI manual. yes, that MPI. no cap, this one's a little helper that tells you how many contiguous chunks (iovs, bestie, iovs) you'd get if you only had max_iov_bytes bytes of room to work with. it's giving "how many lil segments fit in this box", and honestly? obsessed. ✨

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🎀 NAME 🎀

MPIX_Type_iov_len — returns the number of contiguous segments within max_iov_bytes. periodt.

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🌸 SYNOPSIS 🌸

int MPIX_Type_iov_len(MPI_Datatype datatype, MPI_Count max_iov_bytes,
MPI_Count *iov_len, MPI_Count *actual_iov_bytes)

look at that signature, it's literally so clean. two things go in, two things come out. main character energy fr fr. 💅

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🦋 INPUT PARAMETERS 🦋

• datatype — the datatype (a handle). it's the thing you're slicing up, iykyk.
• max_iov_bytes — the maximum number of bytes in the iovs (an integer). this is your budget, babe. don't blow it.

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✨ OUTPUT PARAMETERS ✨

• iov_len — the number of iovs within max_iov_bytes (an integer). so like… how many pieces you got. 🧚
• actual_iov_bytes — the actual number of bytes in the iovs (an integer). the real, honest-to-god byte count, not the budget. no cap.

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💜 THREAD AND INTERRUPT SAFETY 💜

this routine is thread-safe. which means — say it with me — multiple threads can use it safely at the same time without you needing to bring your own thread locks. it's a self-sufficient icon. 👑

BUT. and bestie this is the important but: it is not interrupt safe. 😭 typically that's because it uses memory allocation routines like malloc or other non-MPICH runtime routines, and those lil guys aren't interrupt-safe themselves. so yeah. thread-safe: yes. interrupt-safe: absolutely not. know the difference, it could save your whole job.

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🌈 NOTES FOR FORTRAN 🌈

every single MPI routine in Fortran (except for MPI_WTIME and MPI_WTICK) has an extra argument called ierr tacked on at the end of the argument list. ierr is an integer and it means the exact same thing as the return value of the routine in C. in Fortran, MPI routines are subroutines, and you invoke them with the call statement. that's the whole vibe shift.

also — all MPI objects (like MPI_Datatype, MPI_Comm) are of type INTEGER in Fortran. every single one. 💖

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💀 ERRORS 💀

okay so every MPI routine (except MPI_Wtime and MPI_Wtick) returns an error value — C routines as the return value of the function, and Fortran routines in that last argument. and before that value gets returned? the current MPI error handler gets called. by default, this error handler aborts the MPI job. like, entire program. gone. 💅

but you can change it:

• MPI_Comm_set_errhandler — for communicators
• MPI_File_set_errhandler — for files
• MPI_Win_set_errhandler — for RMA windows

and the MPI-1 routine MPI_Errhandler_set may be used, but its use is deprecated. 🙈 deprecated, bestie. you've been warned.

the predefined error handler MPI_ERRORS_RETURN may be used to cause error values to be returned instead. note that MPI does not guarantee that an MPI program can continue past an error; however, MPI implementations will attempt to continue whenever possible. so like… maybe? no promises. 🤷

here's the error roster:

• MPI_SUCCESS — no error; the MPI routine completed successfully. slay.
• MPI_ERR_ARG — invalid argument. some argument is invalid and isn't identified by a specific error class (e.g., MPI_ERR_RANK).
• MPI_ERR_TYPE — invalid datatype argument. additionally, this error can occur if an uncommitted MPI_Datatype (see MPI_Type_commit) is used in a communication call.
• MPI_ERR_OTHER — other error; use MPI_Error_string to get more information about this error code.

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💖 reminder: this routine is thread-safe but not interrupt-safe, and default error handling will abort your whole MPI job. be normal about it. 🫶

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and that's the page, babes. ✨ this gem dropped on 4/10/2026, and it's from the MPI manual, section 3 — so when you're out here citing it, you're citing MPIX_Type_iov_len(3). go forth and count your iovs, my love. 🎀🌈⭐

<div style="text-align: right">💅 stay iconic 💅</div>