MPI_File_toint(3)

✨ NAME ✨

MPI_File_toint — bestie, this one converts a MPI_File to an integer handle 💖

It's an MPI manual page, and it is exactly as short and sweet as it sounds. Let's get into it 🫶

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✨ SYNOPSIS ✨

int MPI_File_toint(MPI_File file)

That's it. One little function, one little file handle going in, one integer coming out. Slay 💅

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✨ INPUT PARAMETERS ✨

• file — the file handle (it's a handle, ok? that's the whole vibe) 🎀

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✨ THREAD AND INTERRUPT SAFETY ✨

Okay so this is the part where I need you to actually pay attention, bestie, because there's a little catch 👀

This routine is thread-safe. That means you can absolutely let multiple threads hit it at the same time with no user-provided thread locks needed — no mutexes, no nothing, just vibes ✨

However — and this is the important part — the routine is not interrupt safe. Why? Typically because it uses memory allocation routines like malloc, or other non-MPICH runtime routines, and those cuties are themselves not interrupt-safe. So like... don't go interrupting it mid-glow-up, fr fr 😭

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✨ NOTES FOR FORTRAN ✨

Fortran besties, this section is for you 💜

• All MPI routines in Fortran — except for MPI_WTIME and MPI_WTICK — have an additional 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. Same energy, different syntax.
• In Fortran, MPI routines are subroutines, and you invoke them with the call statement. Not a function call, a call. It's giving old-school and honestly? Iconic. 👑

Also: all MPI objects (e.g., MPI_Datatype, MPI_Comm) are of type INTEGER in Fortran. Yes, all of them. No cap. 🌈

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✨ ERRORS ✨

Okay so every single MPI routine — except MPI_Wtime and MPI_Wtick, those two are the rebels 🙈 — returns an error value. C routines return it as the value of the function, and Fortran routines hand it back in that last argument we just talked about.

Here's the tea on what happens before you get that value back ☕:

• The current MPI error handler gets called first.
• By default, this error handler aborts the MPI job. Like, the whole thing. Gone. 💀 So maybe don't just ignore this, bestie.
• You can change 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 also be used — but its use is deprecated. Lowkey don't use it, use the new ones 🎀
• You can use the predefined error handler MPI_ERRORS_RETURN to make error values get returned to you instead of nuking your job.

⚠️ Important caveat: MPI does not guarantee that an MPI program can continue past an error. However, MPI implementations will attempt to continue whenever possible. So like... it's giving hopeful, not promising 🫶

Now the actual error codes you might catch:

• MPI_SUCCESS — No error; MPI routine completed successfully. The good ending, we love to see it ✨
• MPI_ERR_OTHER — Other error; use MPI_Error_string to get more information about this error code. It's giving mysterious on purpose 🔥

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🌸 A lil sign-off 🌸

That's the whole page, bestie — this was the MPI documentation, MPI_File_toint(3), dated 4/10/2026. Go forth and convert those file handles into integers, you absolute main character 👑💖