MPI_WIN_UNLOCK(3)

💅 MPI_WIN_UNLOCK(3) — an Open MPI moment 🎀

okay so bestie, welcome to the Open MPI manual page for MPI_Win_unlock, and honestly? this one's a closer. it wraps up the RMA access epoch that MPI_Win_lock opened. no cap, it's the "ok bye, we're done here" of window locks ✨

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🌸 NAME 🌸

MPI_Win_unlock — bestie it completes an RMA access epoch that was started by a call to MPI_Win_lock. that's the whole vibe. periodt 💅

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✨ SYNTAX ✨

🩵 C Syntax

#include <mpi.h>

int MPI_Win_unlock(int rank, MPI_Win win)

🩵 Fortran Syntax

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

🩵 Fortran 2008 Syntax

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

like, copy-paste these exactly, don't freestyle the signatures, i'm begging 😭

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🫶 INPUT PARAMETERS 🫶

• rank — the rank of the window, and it's a nonnegative integer bestie, they said what they said. 🦋
• win — the window object (handle). the actual window. the main character. 💅

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🎀 OUTPUT PARAMETER 🎀

• ierror — Fortran only! it's the error status, and it's an integer. that's it, that's the output. 🌸

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💖 DESCRIPTION 💖

so. MPI_Win_unlock completes an RMA access epoch started by a call to MPI_Win_lock. and here's the iconic part: RMA operations issued during this period will have completed both at the origin and at the target when the call returns. both sides. locked in. ate and left no crumbs 🔥

locks are used to protect accesses to the locked target window effected by RMA calls issued between the lock and unlock call, and to protect local load/store accesses to a locked local window executed between the lock and unlock call. yes, that whole sentence, it matters 👑

now the exclusive vs. shared tea ☕:

• accesses protected by an exclusive lock will not be concurrent at the window site with other accesses to the same window that are lock protected. (exclusive means exclusive, bestie — vibe check passed 😌)
• accesses protected by a shared lock will not be concurrent at the window site with accesses protected by an exclusive lock to the same window. (shared is chill with shared, but exclusive is not sharing. iykyk 💀)

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😭 ERRORS 😭

almost all MPI routines return an error value, fr fr. C routines return it as the return result of the function, and Fortran routines put it in the last argument. that's just how they do it 🫶

before the error value is returned, the current MPI error handler associated with the communication object (e.g., communicator, window, file) is called. and here's the plot twist: 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. that's a lot, i know, deep breaths, read it twice 🧚

Open MPI includes three predefined error handlers that can be used, and they are lowkey iconic:

• MPI_ERRORS_ARE_FATAL — causes the program to abort all connected MPI processes. dramatic? yes. effective? also yes 💀
• 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, bestie 🌈
• MPI_ERRORS_RETURN — returns an error code to the application. polite. respectful. hands you the problem back 🎁

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

DIY error handling?? we love a self-made queen 👑

⚠️ note that MPI does not guarantee that an MPI program can continue past an error. like, it might just be over. no notes. 💅

see the MPI man page for a full list of MPI error codes. and see the Error Handling section of the MPI-3.1 standard for more information. citations!! we stan a documented queen 📚

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👀 SEE ALSO 👀

• MPI_Win_lock
• MPI_Win_unlock_all

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👑 COPYRIGHT 👑

2003-2026, The Open MPI Community — the whole Open MPI fam. icons only. 🫶

and that's the page bestie!! stay locked, stay unlocked, and don't forget to unlock before you dip 💖

Sep 11, 2026 — MPI_WIN_UNLOCK(3), Open MPI, signing off ✨🎀🦋