MPI_File_iwrite(3)

💖 MPI_File_iwrite(3) — the MPI girlies' guide 💖

okay so bestie, welcome to the MPI manual, page for MPI_File_iwrite 🦋

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✨ NAME ✨

MPI_File_iwrite — nonblocking write using individual file pointer 🌸

like. you're writing to a file. but you are NOT waiting around for it. main character behavior only 💅

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✨ SYNOPSIS ✨

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

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

two versions, both iconic, no notes 🎀

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🌟 INPUT PARAMETERS 🌟

• fh — file handle (handle). it's literally your lil ticket to the file, hold onto it 🫶
• buf — initial address of buffer (choice)
• count — number of elements in buffer (integer). how many. bestie. how many 😭
• datatype — datatype of each buffer element (handle)

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🌈 OUTPUT PARAMETERS 🌈

• request — request object (handle). this is the lil receipt you hold onto so you can check on your write later 👑

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🔥 THREAD AND INTERRUPT SAFETY 🔥

okay this part actually matters so listen up 📢

This routine is thread-safe. what does that mean fr fr? it means you can safely use this routine from multiple threads without needing any user-provided thread locks. no mutexes, no drama, no "wait who has the lock" energy. it just works 💖

BUT. and this is the BUT. it is not interrupt safe. 🫠

usually that's because of memory allocation routines — stuff like malloc, or other non-MPICH runtime routines — that are themselves not interrupt-safe. so like, it's giving thread-safe but not interrupt-safe, and those are two different vibes, don't mix them up 💀

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🎀 NOTES FOR FORTRAN 🎀

• 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 has the same meaning as the return value of the routine in C. periodt.
• in Fortran, MPI routines are subroutines, and they're invoked with the call statement.
• all MPI objects (e.g., MPI_Datatype, MPI_Comm) are of type INTEGER in Fortran. yes bestie, everything is an INTEGER in Fortran, that's just the vibe over there 🦋

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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. 🫡

Before the value is returned, the current MPI error handler is called. By default, this error handler aborts the MPI job. so like, no cap, the default is "everything dies" 😭 you've been warned.

The error handler may be changed with:

• MPI_Comm_set_errhandler (for communicators)
• MPI_File_set_errhandler (for files)
• MPI_Win_set_errhandler (for RMA windows)

The MPI-1 routine MPI_Errhandler_set may be used but its use is deprecated ⚠️ girl don't. it's giving legacy.

The predefined error handler MPI_ERRORS_RETURN may be used to cause error values to be returned. ngl that's lowkey the move if you want to actually survive your errors.

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 it's giving "we'll try our best" energy 🙈

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🍓 the error codes themselves 🍓

• MPI_SUCCESS — No error; MPI routine completed successfully. slay ✨
• MPI_ERR_ARG — Invalid argument. Some argument is invalid and is not 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 that buffer is NOT there 💀
• 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 first, i'm begging 🙏
• MPI_ERR_OTHER — Other error; use MPI_Error_string to get more information about this error code.

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and that's the whole page babes 💅 every option, every caveat, every error code, all of it, exactly as the source had it. no facts were harmed in the making of this rewrite 🫶

this was page MPI_File_iwrite(3) from the MPI manual, dated 4/10/2026 — mwah, go write some files nonblockingly, you absolute icon 👑💖✨