MPI_MPROBE(3)

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💅 MPI_MPROBE(3) — like, the Open MPI manual page, bestie ✨

okay so this is the MPI_Mprobe page from the Open MPI manual and it's genuinely a slay, let me walk you through it 🫶

🌸 NAME 🌸

MPI_Mprobe — blocking matched probe for a message. yep. that's the whole vibe. it peeks at a message and locks it down for you 👑

✨ SYNTAX ✨

💖 C Syntax

#include <mpi.h>

int MPI_Mprobe(int source, int tag, MPI_Comm comm,
     MPI_Message *message, MPI_Status *status)

💖 Fortran Syntax

USE MPI
! or the older form: INCLUDE 'mpif.h'
MPI_MPROBE(SOURCE, TAG, COMM, MESSAGE, STATUS, IERROR)
     INTEGER SOURCE, TAG, COMM, MESSAGE
     INTEGER STATUS(MPI_STATUS_SIZE), IERROR

💖 Fortran 2008 Syntax

USE mpi_f08
MPI_Mprobe(source, tag, comm, message, status, ierror)
     INTEGER, INTENT(IN) :: source, tag
     TYPE(MPI_Comm), INTENT(IN) :: comm
     TYPE(MPI_Message), INTENT(OUT) :: message
     TYPE(MPI_Status) :: status
     INTEGER, OPTIONAL, INTENT(OUT) :: ierror

🎀 INPUT PARAMETERS 🎀

  • source — source rank, or MPI_ANY_SOURCE if you're feeling chaotic (integer).
  • tag — tag value, or MPI_ANY_TAG (integer).
  • comm — the communicator (handle). the group chat, basically.

🦋 OUTPUT PARAMETERS 🦋

  • message — message (handle). this is the golden ticket 🎫
  • status — status object (status).
  • ierror — Fortran only: error status (integer).

🔥 DESCRIPTION 🔥

so. like MPI_Probe and MPI_Iprobe, the MPI_Mprobe and MPI_Improbe operations let you query incoming messages without actually receiving them — but here's the extra slay: MPI_Mprobe and MPI_Improbe give you a mechanism to receive the specific message that was matched, regardless of any other intervening probe or receive operations. no getting sniped by someone else's receive, no cap 🙅‍♀️

this gives your application an opportunity to decide how to receive the message, based on the info the probe returned. in particular — and this is the iconic part — the application may allocate memory for the receive buffer according to the length of the probed message. main character memory management, honestly 💅

a matching probe with MPI_PROC_NULL as source returns message = MPI_MESSAGE_NO_PROC, and the status object returns source = MPI_PROC_NULL, tag = MPI_ANY_TAG, and count = 0. cute, predictable, no drama.

when MPI_Mprobe returns (from a non-MPI_PROC_NULL source), the matched message can then be received by passing the message handle to the MPI_Mrecv or MPI_Imrecv functions. handoff complete, bestie 🫶

😭 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 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. 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. 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, 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 chill 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. like, it might just be over. so maybe don't rely on it 🫣

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_Improbe
  • MPI_Probe
  • MPI_Iprobe
  • MPI_Mrecv
  • MPI_Imrecv
  • MPI_Cancel

2003-2026, The Open MPI Community

and that's the whole page, bestie — go probe something iconic 💖✨🎀🦋🌸

sign-off: this was the MPI_MPROBE(3) page from the Open MPI manual, dated Sep 11, 2026. mwah 💋
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