MPI_WIN_LOCK_ALL(3)

💖 NAME 💖

MPI_Win_lock_all — bestie, this starts an RMA access epoch that locks access to every single process in the window. Yes. All of them. The whole group chat. 💅

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✨ SYNTAX ✨

🍓 C Syntax 🍓

#include <mpi.h>

int MPI_Win_lock_all(int assert, MPI_Win win)

🍓 Fortran Syntax 🍓

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

🍓 Fortran 2008 Syntax 🍓

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

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🎀 INPUT PARAMETERS 🎀

• assert — the program assertion, and it's an integer, okay? 👀
• win — the window object. A handle, bestie. The main character of this whole situation. ✨

🌸 OUTPUT PARAMETER 🌸

• ierror — Fortran only 💅: the error status, and yep, it's an integer.

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🦋 DESCRIPTION 🦋

Okay so listen up. 👂 This starts an RMA access epoch to all the processes in win, and the lock type is MPI_LOCK_SHARED. During that epoch, the calling process can access the window memory on all the processes in win by using RMA operations. Living the dream, lowkey.

Heads up bestie: a window that got locked with MPI_Win_lock_all must be unlocked with MPI_Win_unlock_all. No leaving it on read, no ghosting it. 😭

And no, this routine is not collective — the ALL refers to a lock on all members of the group of the window, not to everybody calling it together. iykyk. 💅

Now, what are locks even for, you ask? They protect accesses to the locked target window effected by RMA calls issued between the lock and the unlock call, and they also protect local load/store accesses to a locked local window executed between the lock and unlock call. 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. 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. That's the whole vibe check, fr fr. 🦋

The assert argument is used to hand over assertions on the context of the call, and those assertions may be used for various optimizations. (See Section 6.4.4 of the MPI-2 Standard if you wanna read the source material yourself.) A value of assert = 0 is always valid — no notes, iconic. ✅ And here's the one assertion value that's supported:

MPI_MODE_NOCHECK 🌈

No other processes will hold or attempt to acquire a conflicting lock while the caller holds the window lock. That's it, that's the tea. ✨

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👑 NOTES 👑

Real talk for a second. 😭 In a client/server environment in which clients connect to a server and create windows that span both the client and the server, if a client or a server that has obtained a lock on such a window and then terminates abnormally, the server or other clients may hang in a MPI_Win_lock_all call, failing to notice that the peer MPI job has terminated. So yeah. Not the vibe. 💀

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💅 ERRORS 💅

Almost all MPI routines return an error value, bestie — C routines give it back as the return result of the function, and Fortran routines put it in the last argument. Periodt.

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. 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 by the mpi_initial_errhandler CLI argument to mpiexec, or by the 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 the other MPI functions.

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

• MPI_ERRORS_ARE_FATAL — causes the program to abort all connected MPI processes. Yeah, all of them. 💀
• 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.
• MPI_ERRORS_RETURN — returns an error code to the application. Very chill of it, honestly. ✨

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. And see the Error Handling section of the MPI-3.1 standard for more information. 📚

See also:

• MPI_Win_unlock_all
• MPI_Win_lock

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💜 COPYRIGHT 💜

2003-2026, The Open MPI Community.

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And that's the whole page, bestie. 💖 This one ships from Open MPI, dated Sep 10, 2026, and MPI_WIN_LOCK_ALL(3) is officially signed, sealed and slayed. Now go lock all those windows — you got this. 👑✨