MPI_Session_detach_buffer(3)

💅 MPI_Session_detach_buffer — bestie edition

okay so real talk, this one lives in the MPI manual, section 3, and it's called MPI_Session_detach_buffer. yes it's a mouthful. yes it's iconic. let's go 🫶

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✨ NAME ✨

MPI_Session_detach_buffer — removes an existing buffer (for use in MPI_Bsend etc) in the session

like... it's giving "we're done here, take your buffer back" energy 💀

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✨ SYNOPSIS ✨

int MPI_Session_detach_buffer(MPI_Session session, void *buffer_addr,
int *size)

int MPI_Session_detach_buffer_c(MPI_Session session, void *buffer_addr,
MPI_Count *size)

two flavours, same vibe. the _c one is just out here holding a bigger counter bestie ✨

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✨ INPUT PARAMETERS ✨

• session — session (handle). it's the session, girl. the handle. that's the whole thing 🎀

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✨ OUTPUT PARAMETERS ✨

• buffer_addr — initial buffer address (choice)
• size — buffer size, in bytes (integer)

both of these come out of the call, so don't you dare think you're feeding them in 💅

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🧚 NOTES FOR FORTRAN 🧚

So 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. In Fortran, MPI routines are subroutines, and they're invoked with the call statement. no cap 📣

Also: all MPI objects (e.g., MPI_Datatype, MPI_Comm) are of type INTEGER in Fortran. that's just how Fortran rolls 🍓

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🔥 ERRORS 🔥

okay listen up because this part is important and also a little scary 😭

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. like, it just ends everything. the whole job. bye 👑

The error handler may 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 — so like, it's still there but do not make it your main character moment, bestie 🙈

The predefined error handler MPI_ERRORS_RETURN may be used to cause error values to be returned. 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... sometimes you get to keep going, sometimes you don't. vibe check unclear 🦋

Here's the lineup of error codes:

• 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). something's wrong and it's being mysterious about it 💀
• MPI_ERR_SESSION — Invalid session handle
• MPI_ERR_OTHER — Other error; use MPI_Error_string to get more information about this error code.

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👀 SEE ALSO 👀

• MPI_Session_attach_buffer
• MPI_Bsend

(the attach/detach duo, iykyk 💜)

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and that's the whole page, fr fr. this one's from MPI_Session_detach_buffer(3), dated 4/10/2026 — go off, session buffer, you ate 🎀✨💖