MPI_COMM_GET_PARENT(3)

💖 MPI_COMM_GET_PARENT(3) 💖

okay so bestie, this iconic little page is from the Open MPI manual — page MPI_COMM_GET_PARENT(3) — and we're about to make parent communicators make sense. 🫶

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🌸 NAME 🌸

MPI_Comm_get_parent — returns the parent intercommunicator of the current spawned process. That's the whole assignment, and it ate. 💅

✨ SYNTAX ✨

🧊 C Syntax 🧊

          #include <mpi.h>

          int MPI_Comm_get_parent(MPI_Comm *parent)

🧊 Fortran Syntax 🧊

          USE MPI
          ! or the older form: INCLUDE 'mpif.h'
          MPI_COMM_GET_PARENT(PARENT, IERROR)
               INTEGER PARENT, IERROR

🧊 Fortran 2008 Syntax 🧊

          USE mpi_f08
          MPI_Comm_get_parent(parent, ierror)
               TYPE(MPI_Comm), INTENT(OUT) :: parent
               INTEGER, OPTIONAL, INTENT(OUT) :: ierror

📤 OUTPUT PARAMETERS 📤

• parent — The parent communicator (handle).
• ierror — Fortran only: Error status (integer).

🌈 DESCRIPTION 🌈

okay so picture this: if a process was started with MPI_Comm_spawn or MPI_Comm_spawn_multiple, then MPI_Comm_get_parent hands you back the “parent” intercommunicator of the current process. This parent intercommunicator is created implicitly inside of MPI_Init, and it's the same intercommunicator returned by the spawn call made in the parents. no cap. 💫

If the process was not spawned, MPI_Comm_get_parent returns MPI_COMM_NULL. And after the parent communicator is freed or disconnected, MPI_Comm_get_parent also returns MPI_COMM_NULL. That's the vibe check. ✅

💌 NOTES 💌

MPI_Comm_get_parent returns a handle to a single intercommunicator. Calling MPI_Comm_get_parent a second time returns a handle to the same intercommunicator — same one, bestie. 🫶

Freeing the handle with MPI_Comm_disconnect or MPI_Comm_free will cause other references to the intercommunicator to become invalid (dangling). Note that calling MPI_Comm_free on the parent communicator is not useful. So like… don't do the useless thing, and definitely don't leave dangling references lying around. 🚩

🚨 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. That's the baseline, okay? 💅

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.
• 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.

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. 🫠

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_Comm_spawn
• MPI_Comm_spawn_multiple

📜 COPYRIGHT 📜

2003-2026, The Open MPI Community

xoxo, Open MPI 💖 — Sep 11, 2026 — MPI_COMM_GET_PARENT(3)