MPI_File_iwrite_all(3)

💖 MPI_File_iwrite_all(3) — the MPI manual page, bestie edition 💖

okay so this is a page from the MPI manual, and today's main character is MPI_File_iwrite_all 🎀

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✨ NAME ✨

MPI_File_iwrite_all — nonblocking collective write using the individual file pointer, no cap 💅

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🌸 SYNOPSIS 🌸

int MPI_File_iwrite_all(MPI_File fh, const void *buf, int count,
       MPI_Datatype datatype, MPI_Request *request)

int MPI_File_iwrite_all_c(MPI_File fh, const void *buf, MPI_Count count,
       MPI_Datatype datatype, MPI_Request *request)

two whole flavors, we love options 🫶

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💜 INPUT PARAMETERS 💜

• fh — the file handle (type: handle). it's giving "which file are we even writing to" energy 🔥
• buf — initial address of the buffer (type: choice). this is where your precious little bytes live 🍓
• count — number of elements sitting in that buffer (type: integer) ✨
• datatype — datatype of each buffer element (type: handle). literally the blueprint for what each element IS 💅

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🦋 OUTPUT PARAMETERS 🦋

• request — request object (type: handle). this is your little receipt bestie, hold onto it 👑

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🧚 THREAD AND INTERRUPT SAFETY 🧚

okay so this routine is thread-safe. which means what exactly? it means multiple threads can use it safely, and you do NOT need to bring your own user-provided thread locks. that's the dream, honestly 😌✨

BUT. and this is the important but 🚨 the routine is not interrupt safe. why, you ask? typically it's because of memory allocation routines like malloc, or other non-MPICH runtime routines, that are themselves not interrupt-safe. so like, it's not this function's fault, it's the company it keeps 💀

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🌈 NOTES FOR FORTRAN 🌈

• every single MPI routine in Fortran (except MPI_WTIME and MPI_WTICK) gets an extra argument called ierr tacked onto the end of the argument list. ierr is an integer and means exactly 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 📞
• all MPI objects (e.g., MPI_Datatype, MPI_Comm) are of type INTEGER in Fortran. periodt 💅

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😭 ERRORS 😭

every MPI routine (except MPI_Wtime and MPI_Wtick) returns an error value — C routines as the value of the function, and Fortran routines in the last argument. before that value comes back to you, the current MPI error handler gets called. and by default? this error handler aborts the MPI job. yeah. dramatic 💀

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). the MPI-1 routine MPI_Errhandler_set may still be used, but its use is deprecated — so maybe don't 👀

you can also use the predefined error handler MPI_ERRORS_RETURN to make error values get returned instead of nuking everything. and ngl, MPI does not guarantee that an MPI program can continue past an error; however, MPI implementations will attempt to continue whenever possible. optimistic of them fr fr 🫶

here's the error code lineup:

• 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_BUFFER — invalid buffer pointer. usually a null buffer where one is not valid. bestie. why is the buffer 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 👑
• MPI_ERR_OTHER — other error; use MPI_Error_string to get more information about this error code 🔍

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🌟 SEE ALSO 🌟

that's the whole page bestie, no SEE ALSO here, we're self-contained 💖

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reminder: every flag, arg, default and error code above is exactly as written in the original — the vibes are mine, the facts are the manpage's 💅

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and that's a wrap 🎀 this was MPI_File_iwrite_all(3) from the MPI manual, dated 4/10/2026, brought to you by the MPI docs themselves. stay thread-safe, stay non-interruptible, and don't forget to commit your datatypes 🦋✨ bye bestie! 👑