MPI_COMM_FREE(3)

💅 MPI_Comm_free 💅

okay bestie, this is the Open MPI manual page for MPI_COMM_FREE(3) — folding that manual name in right here so we’re not copying the header line like a plain old manpage. ✨

✨ NAME ✨

MPI_Comm_free — mark a communicator object for deallocation. That’s the vibe: you’re not instantly nuking it, you’re marking it for deallocation, and the handle gets set to MPI_COMM_NULL. 💅

🛠️ SYNTAX 🛠️

C Syntax

          #include <mpi.h>

          int MPI_Comm_free(MPI_Comm *comm)

Fortran Syntax

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

Fortran 2008 Syntax

          USE mpi_f08
          MPI_Comm_free(comm, ierror)
               TYPE(MPI_Comm), INTENT(INOUT) :: comm
               INTEGER, OPTIONAL, INTENT(OUT) :: ierror

📥 INPUT PARAMETER 📥

• comm — communicator to be destroyed (handle). 🫶

📤 OUTPUT PARAMETER 📤

• ierror — Fortran only: error status (integer). 😌

🌈 DESCRIPTION 🌈

This operation marks the communicator object for deallocation. The handle is set to MPI_COMM_NULL. Any pending operations that use this communicator will complete normally; the object is actually deallocated only if there are no other active references to it. This call applies to intracommunicators and intercommunicators. Upon actual deallocation, the delete callback functions for all cached attributes (see the “Caching” section in the “Groups, Contexts, and Communicators” chapter in the MPI Standard) are called in arbitrary order. 🌀

🧠 NOTES 🧠

Heads up, bestie: it is not defined by the MPI standard what happens if the delete_fn callback invokes other MPI functions. In Open MPI, it is not valid for delete_fn callbacks (or any of their children) to add or delete attributes on the same object on which the delete_fn callback is being invoked. 💀

💀 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.

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_delete_attr

🎀 COPYRIGHT 🎀

2003-2026, The Open MPI Community

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🍓 source/version: 2003-2026, The Open MPI Community • page date: Sep 11, 2026 • manual: Open MPI MPI_COMM_FREE(3) — bye bestie! 🫶