MPI_WIN_ATTACH(3)

💅 MPI_Win_attach — the Open MPI girlie's guide 💅

ok so bestie, we're doing MPI_Win_attach(3) today and honestly? iconic behavior. this is the Open MPI manual page for MPI_Win_attach, MPI_Win_detach — the one-sided MPI calls that attach / detach a memory region to / from a window object for RMA operations. slay. let's go 🫶

---

✨ SYNTAX ✨

🌸 C Syntax

#include <mpi.h>

MPI_Win_attach(MPI_Win win, void *base, MPI_Aint size)

MPI_Win_detach(MPI_Win win, void *base)

🌸 Fortran Syntax

USE MPI
! or the older form: INCLUDE 'mpif.h'
MPI_WIN_ATTACH(WIN, BASE, SIZE, IERROR)
     <type> BASE(*)
     INTEGER(KIND=MPI_ADDRESS_KIND) SIZE
     INTEGER WIN, IERROR

MPI_WIN_DETACH(WIN, BASE, IERROR)
     <type> BASE(*)
     INTEGER WIN, IERROR

🌸 Fortran 2008 Syntax

USE mpi_f08
MPI_Win_attach(win, base, size, ierror)
     TYPE(MPI_Win), INTENT(IN) :: win
     TYPE(*), DIMENSION(..), INTENT(IN) :: base
     INTEGER(KIND=MPI_ADDRESS_KIND), INTENT(IN) :: size
     INTEGER, OPTIONAL, INTENT(OUT) :: ierror

MPI_Win_detach(win, base, ierror)
     TYPE(MPI_Win), INTENT(IN) :: win
     TYPE(*), DIMENSION(..), INTENT(IN) :: base
     INTEGER, OPTIONAL, INTENT(OUT) :: ierror

---

💖 INPUT PARAMETERS 💖

• win — a window that was created with MPI_Win_create_dynamic. yes, that specific one, don't try to finesse it with a different create call, it's not gonna eat 💀
• base — initial address of window (choice). like the starting address, the beginning of the vibe ✨
• size — size of window in bytes (nonnegative integer). nonnegative, ok? we do not do negative bytes in this house 🙈

---

🎀 OUTPUT PARAMETERS 🎀

• win — window object returned by the call (handle). it's giving handle energy 👑
• ierror — Fortran only: error status (integer). Fortran besties only, sorry C girlies 💅

---

🦋 DESCRIPTION 🦋

okay so MPI_Win_attach is a one-sided MPI communication call and what it does is attach a memory region of size bytes starting at address base to a window for RMA access. literally just snapping a chunk of memory into your window like 🫰

the window win must have been created using MPI_Win_create_dynamic. no cap, that's a requirement.

multiple non-overlapping memory regions may be attached to the same dynamic window — cute, stack them up, we love a collection ✨

attaching overlapping memory regions to the same dynamic window is erroneous. do not do that. it's not a vibe. 😭

if the base value used by MPI_Win_attach was allocated by MPI_Alloc_mem, the size of the window can be no larger than the value set by the MPI_Alloc_mem function. so keep it within bounds bestie, that's the rule 💜

MPI_Win_detach can be used to detach a previously attached memory region from win. the memory address base and win must match arguments passed to a previous call to MPI_Win_attach — like, they have to be the same arguments, it's a matching puzzle piece situation 🧩

---

🌈 NOTES 🌈

use memory allocated by MPI_Alloc_mem to guarantee properly aligned window boundaries (such as word, double-word, cache line, page frame, and so on). alignment matters, she's particular about her boundaries, we respect it 👑

---

🔥 ERRORS 🔥

almost all MPI routines return an error value; C routines as the return result of the function and Fortran routines in the last argument. classic MPI behavior fr fr.

before the error value is returned, the current MPI error handler associated with the communication object (e.g., communicator, window, file) is called. if no communication object is associated with the MPI call, then the call is considered attached to MPI_COMM_SELF and will call the associated MPI error handler. when MPI_COMM_SELF is not initialized (i.e., before MPI_Init/MPI_Init_thread, after MPI_Finalize, or when using the Sessions Model exclusively) the error raises the initial error handler. the initial error handler can be changed by calling MPI_Comm_set_errhandler on MPI_COMM_SELF when using the World model, or the mpi_initial_errhandler CLI argument to mpiexec or info key to MPI_Comm_spawn/MPI_Comm_spawn_multiple. and if no other appropriate error handler has been set, then the MPI_ERRORS_RETURN error handler is called for MPI I/O functions and the MPI_ERRORS_ABORT error handler is called for all other MPI functions. that's a whole lot of handler talk but like, now you know 💅

Open MPI includes three predefined error handlers that can be used:

• MPI_ERRORS_ARE_FATAL — causes the program to abort all connected MPI processes. dramatic much? 💀
• MPI_ERRORS_ABORT — an error handler that can be invoked on a communicator, window, file, or session. when called on a communicator, it acts as if MPI_Abort was called on that communicator. if called on a window or file, acts as if MPI_Abort was called on a communicator containing the group of processes in the corresponding window or file. if called on a session, aborts only the local process. versatile icon ✨
• MPI_ERRORS_RETURN — returns an error code to the application. the chill one, hands you the receipt and lets you deal 🧾

MPI applications can also implement their own error handlers by calling:

• MPI_Comm_create_errhandler then MPI_Comm_set_errhandler
• MPI_File_create_errhandler then MPI_File_set_errhandler
• MPI_Session_create_errhandler then MPI_Session_set_errhandler or at MPI_Session_init
• MPI_Win_create_errhandler then MPI_Win_set_errhandler

note that MPI does not guarantee that an MPI program can continue past an error. so like… plan accordingly 😬

see the MPI man page for a full list of MPI error codes. 👀

see the Error Handling section of the MPI-3.1 standard for more information. iykyk 📚

---

👑 COPYRIGHT 👑

2003-2026, The Open MPI Community

---

and that's the whole page bestie — big love to the Open MPI Community, copyright 2003-2026, page dated Sep 11, 2026. go forth and attach your memory regions responsibly, non-overlapping only, mwah 💖🎀🦋🌸