MPI_WIN_FLUSH(3)

🌸 NAME 🌸

MPI_Win_flush, MPI_Win_flush_all — okay so bestie, this is the one that completes all outstanding RMA operations at both the origin and the target. That's it, that's the whole job, and it does it flawlessly. 💅

(also hi yes this is the Open MPI manual page, welcome to the group chat 🫶)

---

✨ SYNTAX ✨

💻 C Syntax

#include <mpi.h>

int MPI_Win_flush (int rank, MPI_Win win)

int MPI_Win_flush_all (MPI_Win win)

🧚 Fortran Syntax

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

MPI_WIN_FLUSH_ALL(WIN, IERROR)
     INTEGER WIN, IERROR

🦋 Fortran 2008 Syntax

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

MPI_Win_flush_all(win, ierror)
     TYPE(MPI_Win), INTENT(IN) :: win
     INTEGER, OPTIONAL, INTENT(OUT) :: ierror

---

🎀 INPUT PARAMETERS 🎀

• rank — the rank of the window, and it's a nonnegative integer, no negative vibes allowed bestie 🙈
• win — the window object, aka the handle 👑

---

💖 OUTPUT PARAMETER 💖

• ierror — Fortran only, babes: this is the error status, an integer. 💌

---

🦋 DESCRIPTION 🦋

So MPI_Win_flush completes all outstanding RMA operations initiated by the calling process to the target rank on the specified window. And when I say completes, I mean it completes them both at the origin and at the target — like, full circle, no loose ends, everything ate and left no crumbs. 💅

Meanwhile MPI_Win_flush_all completes all outstanding RMA operations to all targets. All of them. Every single one. Iconic behaviour honestly.

⚠️ Important vibe check: this can only be called from within a passive target epoch. Do not come at it from anywhere else, it will not be the moment you think it is. 😭

---

😭 ERRORS 😭

Okay so, real talk. Almost all MPI routines return an error value — C routines give 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 associated with the communication object (think: communicator, window, file) gets called. And if no communication object is associated with the MPI call? Then the call is considered attached to MPI_COMM_SELF and it will call the associated MPI error handler. 👀

When MPI_COMM_SELF is not initialized — that means before MPI_Init / MPI_Init_thread, after MPI_Finalize, or when using the Sessions Model exclusively — the error raises the initial error handler. And 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 via the mpi_initial_errhandler CLI argument to mpiexec, or the info key to MPI_Comm_spawn / MPI_Comm_spawn_multiple. Slay, options. ✨

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, and they are:

• MPI_ERRORS_ARE_FATAL — causes the program to abort all connected MPI processes. Yeah. Everyone. Bestie it's giving extinction event 💀
• 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, it 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, it aborts only the local process. Context is everything, periodt.
• MPI_ERRORS_RETURN — returns an error code to the application. Chill, lowkey, hands the problem back to you. 🫶

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. Like, no promises bestie, that's just how it is.

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_flush_local
• MPI_Win_lock
• MPI_Win_lock_all

---

👑 COPYRIGHT 👑

2003-2026, The Open MPI Community

---

and that's the whole page bestie 🎀 huge shoutout to the Open MPI girlies — this one's from the Open MPI source, dated Sep 10, 2026, and the page is MPI_WIN_FLUSH(3). go flush something ✨💅