MPI_WIN_FLUSH_ALL(3)

📦

version 5.0.10 · 4 versions

💖 bestie alert 💖 you're in the Open MPI manual, section 3, and the page is MPI_WIN_FLUSH_ALL — aka MPI_Win_flush_all, riding shotgun with its twin MPI_Win_flush. 🦋

okay so the whole vibe of this page, in one breath: complete all outstanding RMA operations at both the origin and the target. That's the assignment. Periodt. ✨

🌸 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 cap. 💅
win — the window object (handle). The whole little universe you're flushing into. 🌈

🎀 OUTPUT PARAMETER 🎀

ierror — Fortran only: error status (integer). The Fortran girlies get the receipts at the end of the call, not as the return value. 🫶

👑 DESCRIPTION 👑

MPI_Win_flush completes all outstanding RMA operations initiated by the calling process to the target rank on the specified window. And bestie, "completes" means both sides — the operations are completed at the origin and at the target. Not one, not the other. Both. Fr fr. 😤

MPI_Win_flush_all does the same thing but sends the energy to all targets. Every single one. No picking favorites.

⚠️ BIG ONE, DO NOT SKIP: this can ONLY be called from within a passive target epoch. Not an active one. Not "eh, close enough." Passive only. If you're in the wrong epoch, that's on you. 💀

💀 ERRORS 💀

Okay so almost all MPI routines hand you back an error value — C routines give it to you as the return result of the function, and Fortran routines tuck it into the last argument. 💌

Before that error value comes back to you, 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 is considered attached to MPI_COMM_SELF and it'll call the associated MPI error handler. 🫠

And when MPI_COMM_SELF isn't initialized — that's 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. You can change that initial error handler 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. ✨

If no other appropriate error handler has been set, then MPI_ERRORS_RETURN gets called for MPI I/O functions, and MPI_ERRORS_ABORT gets called for all other MPI functions.

Open MPI ships three predefined error handlers you can use, and they are:

MPI_ERRORS_ARE_FATAL — causes the program to abort all connected MPI processes. Everyone. Gone. 💀
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. The chill one. 🫶

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, don't count on walking it off. 😭

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.