MPIX_Type_iov(3)

💖 MPIX_Type_iov — bestie edition ✨

okay so this is page MPIX_Type_iov(3) from the MPI manual, and honestly? she's giving "let me hand you the contiguous segments you asked for, starting from an iov offset." main character energy fr fr 💅

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🌸 NAME 🌸

MPIX_Type_iov — returns contiguous segments starting from an iov offset. that's it, that's the whole job, and she does it flawlessly ✨

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🦋 SYNOPSIS 🦋

int MPIX_Type_iov(MPI_Datatype datatype, MPI_Count iov_offset, MPIX_Iov *iov,
MPI_Count max_iov_len, MPI_Count *actual_iov_len)

like yes, five args, no cap, she's a whole function 💜

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🎀 INPUT PARAMETERS 🎀

• datatype — the datatype (handle). that's your girl, your handle, your everything 🫶
• iov_offset — number of contiguous segments to skip (integer). lowkey just "scroll past this many" 🙈
• max_iov_len — capacity for the segments array (integer). how much room you're giving her to work with 💅

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💖 OUTPUT PARAMETERS 💖

• iov — contiguous segments array for output (None). the actual goods, freshly delivered ⭐
• actual_iov_len — actual number of segments in output (integer). not the capacity, the reality, the truth tea ☕

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🔥 THREAD AND INTERRUPT SAFETY 🔥

this routine is thread-safe, bestie. meaning multiple threads can safely use it at the same time and you don't have to bring your own thread locks. no user-provided locking required, she handles herself 💅

however — and this is the part where we get a lil serious — the routine is not interrupt safe. typically this is because it uses memory allocation routines like malloc or other non-MPICH runtime routines, and those are themselves not interrupt-safe. so like, threads? slay. interrupts? not her moment 😭

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🌈 NOTES FOR FORTRAN 🌈

okay Fortran besties, listen up 👑

all MPI routines in Fortran (except for MPI_WTIME and MPI_WTICK) have an additional argument ierr at the end of the argument list. ierr is an integer and it means the same thing as the return value of the routine in C. so it's like the vibe translator between the two languages 🧚

also in Fortran, MPI routines are subroutines, and you invoke them with the call statement. iconic behavior, honestly.

and all MPI objects (e.g., MPI_Datatype, MPI_Comm) are of type INTEGER in Fortran. yes, even the ones that feel like they should be fancier. INTEGER. periodt 💜

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💀 ERRORS 💀

so, all MPI routines (except MPI_Wtime and MPI_Wtick) return an error value — C routines as the value of the function, and Fortran routines in the last argument. and before that value comes back, the current MPI error handler gets called. by default, this error handler aborts the MPI job — like, the whole thing, gone, done 💀

the error handler can be changed with MPI_Comm_set_errhandler (for communicators), MPI_File_set_errhandler (for files), and MPI_Win_set_errhandler (for RMA windows). the MPI-1 routine MPI_Errhandler_set may be used but its use is deprecated — like, okay boomer, we moved on 🙈

you can also use the predefined error handler MPI_ERRORS_RETURN to make error values get returned instead of just nuking everything. and ngl, note that MPI does not guarantee an MPI program can continue past an error; however, MPI implementations will attempt to continue whenever possible. so it's giving "we'll try" not "we promise" 🥲

here's the error roster:

• MPI_SUCCESS — no error; MPI routine completed successfully. the dream, the icon, the moment ✨
• MPI_ERR_ARG — invalid argument. some argument is invalid and is not identified by a specific error class (e.g., MPI_ERR_RANK). she saw an arg and said "not today" 😭
• 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. commit your types, bestie, seriously 💅
• MPI_ERR_OTHER — other error; use MPI_Error_string to get more information about this error code. the catch-all, the "idk but ask her" option 🫶

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vibe check complete 💖 every flag, every arg, every error code accounted for. no skips, no shortcuts, we keep the facts and serve the flavor 🎀

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and that's the page!! 🦋 this was MPIX_Type_iov(3) from the MPI manual, dated 4/10/2026, and yes the footer says MPIX_Type_iov(3) too because she's consistent, she's committed, she's that girl 👑💜 thanks for reading, love u, bye!! ✨