MPI_WIN_WAIT(3)

💫 MPI_WIN_WAIT 💫

okay bestie so this is a page from the Open MPI manual — it's MPI_WIN_WAIT(3) — and we're gonna talk about MPI_Win_wait, which is the moment your exposure epoch ✨ends✨. no cap, this is a good one. 🎀

---

🌸 NAME 🌸

MPI_Win_wait — completes an RMA exposure epoch started by a call to MPI_Win_post on win 💅

---

✨ SYNTAX ✨

🍓 C Syntax

#include <mpi.h>

int MPI_Win_wait(MPI_Win win)

🦋 Fortran Syntax

USE MPI
! or the older form: INCLUDE 'mpif.h'
MPI_WIN_WAIT( WIN, IERROR)
     INTEGER  WIN, IERROR

🧚 Fortran 2008 Syntax

USE mpi_f08
MPI_Win_wait(win, ierror)
     TYPE(MPI_Win), INTENT(IN) :: win
     INTEGER, OPTIONAL, INTENT(OUT) :: ierror

---

💖 INPUT PARAMETERS 💖

• win — window object (handle). literally your window, your main character. 🪟

---

🌈 OUTPUT PARAMETERS 🌈

• ierror — Fortran only: error status (integer). 🙈

---

👑 DESCRIPTION 👑

so MPI_Win_wait is a one-sided MPI communication synchronization call, and what it does is complete an RMA exposure epoch that got started by a call to MPI_Win_post on win. 🫶

here's the vibe: this call matches the calls to MPI_Win_complete(win) that each of the processes who were granted access to the window during this epoch goes and makes. and the call to MPI_Win_wait blocks until all those matching calls to MPI_Win_complete have happened. that's the whole point — it guarantees that all those origin processes have finished up their RMA accesses to the local window. 🧠✨

so like, when this call returns? every single one of those RMA accesses will have completed at the target window. periodt. 🔥

---

💀 ERRORS 💀

almost all MPI routines return an error value — C routines hand it back as the return result of the function, and Fortran routines put it in the last argument. 😌

before that error value gets returned, the current MPI error handler that's associated with the communication object (think: communicator, window, file) gets called. if there's no communication object associated with the MPI call, then the call counts as attached to MPI_COMM_SELF and it'll call the associated MPI error handler. and when MPI_COMM_SELF isn't initialized — i.e. before MPI_Init/MPI_Init_thread, after MPI_Finalize, or when you're using the Sessions Model exclusively — the error raises the initial error handler. 🫠

that initial error handler can be changed by calling MPI_Comm_set_errhandler on MPI_COMM_SELF when you're using the World model, or by the mpi_initial_errhandler CLI argument to mpiexec, or the 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. 😭

Open MPI ships with three predefined error handlers you can use:

• MPI_ERRORS_ARE_FATAL — causes the program to abort all connected MPI processes. yes, all of them. 🔥
• MPI_ERRORS_ABORT — an error handler that can be invoked on a communicator, window, file, or session. when it's called on a communicator, it acts as if MPI_Abort was called on that communicator. if it's called on a window or file, it acts as if MPI_Abort was called on a communicator containing the group of processes in the corresponding window or file. if it's called on a session, it aborts only the local process. 💅
• MPI_ERRORS_RETURN — returns an error code to the application. nice and chill. 🍓

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 🎀

not me reminding you that MPI does not guarantee an MPI program can continue past an error. like, fr fr. ⚠️

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. 🧠

see also:

• MPI_Win_post

---

🫶 Copyright 🫶

2003-2026, The Open MPI Community

---

and that's the whole page bestie!! 💖 this was MPI_Win_wait from the Open MPI docs, dated Sep 10, 2026 — MPI_WIN_WAIT(3), slay, go forth and close your exposure epochs responsibly. mwah. 💅✨🌈