MPI_WIN_START(3)

💅 MPI_Win_start — starts an RMA access epoch for win 💅

okay so bestie, welcome to the Open MPI manual page for MPI_Win_start ✨ this is the one-sided-communication girlie who opens up an RMA access epoch and honestly? she ate. let's get into it 🎀

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🌸 SYNTAX 🌸

💖 C Syntax

#include <mpi.h>

int MPI_Win_start(MPI_Group group, int assert, MPI_Win win)

🦋 Fortran Syntax

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

🧚 Fortran 2008 Syntax

USE mpi_f08
MPI_Win_start(group, assert, win, ierror)
     TYPE(MPI_Group), INTENT(IN) :: group
     INTEGER, INTENT(IN) :: assert
     TYPE(MPI_Win), INTENT(IN) :: win
     INTEGER, OPTIONAL, INTENT(OUT) :: ierror

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⭐ INPUT PARAMETERS ⭐

• group — the group of target processes, as a handle 👑 these are the lucky processes your RMA calls are allowed to touch.
• assert — program assertion, an integer 💅 little hint-y hint you pass along so the library can optimize.
• win — the window object, handle edition 🪟

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💜 OUTPUT PARAMETERS 💜

• ierror — Fortran only: the error status, an integer 😭 hopefully zero, but you know how it is.

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🌈 DESCRIPTION 🌈

okay so here's the vibe: MPI_Win_start is a one-sided MPI communication synchronization call, and what it does is start an RMA access epoch for win ✨ that's the whole gig. main character energy fr.

here's the rules, no cap: RMA calls that you issue on win during this epoch must access only windows at processes in group. and every single process in group has to issue a matching call to MPI_Win_post — like, it's giving mutual commitment, iykyk 🫶. also, MPI_Win_start is allowed to block until the corresponding MPI_Win_post calls have been executed, but it is not required to — so don't come for her if she doesn't wait around 💀.

now, the assert argument is used to provide assertions on the context of the call, and those can be used for various optimizations 🔥 (peep Section 6.4.4 of the MPI-2 Standard). a value of assert = 0 is always valid — the safe lil default, love that for us. the following assertion value is supported:

• MPI_MODE_NOCHECK — when this value is passed in to this call, the library assumes that the post call on the target has been called, and it is not necessary for the library to check to see if such a call has been made ⚡ so it just trusts you. iconic, slightly risky, we respect it.

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💀 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 🎀 noted and memorized bestie.

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. 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 includes three predefined error handlers that can be used:

• MPI_ERRORS_ARE_FATAL — causes the program to abort all connected MPI processes 💀 yeah. all of them. dramatic but fair.
• 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 🎀
• MPI_ERRORS_RETURN — returns an error code to the application 🌸 the polite 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. so like… don't count on it bestie 😭

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 📚

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🦋 SEE ALSO 🦋

• MPI_Win_post
• MPI_Win_complete

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👑 COPYRIGHT 👑

2003-2026, The Open MPI Community 💜

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and that's the whole page diva ✨ header said MPI_WIN_START(3), the manual's Open MPI (told you at the top 🎀), and the footer was giving version-of-Sep 11, 2026 — so yeah, drop date Sep 11, 2026, MPI_WIN_START(3) energy, and the Open MPI crew said 2003-2026, The Open MPI Community. slay, go start some epochs 💅🌈