MPI_File_write_ordered_begin(3)

✨ MPI_File_write_ordered_begin ✨

okay bestie, welcome to section 3 of the MPI manual 💅 this one's called MPI_File_write_ordered_begin, and it is genuinely so useful once you get it.

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🌸 NAME 🌸

MPI_File_write_ordered_begin — Begin a split collective write using shared file pointer

like. it literally just starts the thing. it doesn't finish it. we'll get there, i promise 🫶

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🦋 SYNOPSIS 🦋

int MPI_File_write_ordered_begin(MPI_File fh, const void *buf, int count,
MPI_Datatype datatype)

int MPI_File_write_ordered_begin_c(MPI_File fh, const void *buf,
MPI_Count count, MPI_Datatype datatype)

two flavors, same energy: the classic one and the _c one that takes an MPI_Count instead of an int for count. pick your fighter ⭐

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🎀 INPUT PARAMETERS 🎀

• fh — file handle (handle). this is your file's little ID card, you get it from opening the file.
• buf — initial address of buffer (choice). the actual data situation lives here.
• count — number of elements in buffer (integer). how many of the little guys.
• datatype — datatype of each buffer element (handle). tells MPI what kind of element we're counting, bestie.

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💜 THREAD AND INTERRUPT SAFETY 💜

good news first: this routine is thread-safe 🔥 that means multiple threads can use it safely with zero user-provided thread locks needed. no cap. you don't have to build your own little lock fortress around it.

but. okay. listen. it is not interrupt safe 😭 typically that's because of memory allocation routines like malloc or other non-MPICH runtime routines that are themselves not interrupt-safe. so don't be out here interrupting it, fr fr.

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🌈 NOTES FOR FORTRAN 🌈

Fortran besties this part is for you 💖

all MPI routines in Fortran (except for MPI_WTIME and MPI_WTICK) have an extra argument ierr at the very end of the argument list. ierr is an integer and it means the 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.

also: all MPI objects (e.g., MPI_Datatype, MPI_Comm) are of type INTEGER in Fortran.

not me having to remember the extra ierr argument every single time 🙈 just… put it at the end. every time. periodt.

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⭐ ERRORS ⭐

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. before that value comes back, the current MPI error handler gets called. by default, this error handler aborts the MPI job 💀 yeah. whole job. gone.

you can swap the error handler with MPI_Comm_set_errhandler (for communicators), MPI_File_set_errhandler (for files), and MPI_Win_set_errhandler (for RMA windows). there's also the MPI-1 routine MPI_Errhandler_set, which may be used, but its use is deprecated — so like, don't, unless you truly must.

the predefined error handler MPI_ERRORS_RETURN may be used to cause error values to be returned instead of the whole abort situation. and note: MPI does not guarantee that an MPI program can continue past an error; however, MPI implementations will attempt to continue whenever possible. so like… sometimes it survives. sometimes it doesn't. main character energy, unpredictable 💅

• MPI_SUCCESS — No error; MPI routine completed successfully. 🎉 iconic, we love her.
• MPI_ERR_BUFFER — Invalid buffer pointer. Usually a null buffer where one is not valid. bestie. why is it null.
• MPI_ERR_COUNT — Invalid count argument. Count arguments must be non-negative; a count of zero is often valid.
• 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, i'm begging 🫶
• MPI_ERR_OTHER — Other error; use MPI_Error_string to get more information about this error code. the catch-all. the mysterious one. go ask MPI_Error_string.

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👑 SEE ALSO 👑

nope, this page doesn't list any cross-references — so that's a wrap, bestie 🎀 go forth and split-collectively-write ✨

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lowkey a slay, highkey a classic. stay safe, return MPI_SUCCESS, and always remember: this one only begins it 😌

💖 this page came to you from the MPI manual, and this version is dated 4/10/2026 — MPI_File_write_ordered_begin(3), that's her full name, she's iconic, she's thread-safe, she's not interrupt safe. bye bestie 🦋🌸💜