MPI_MRECV(3)

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, in ubuntu stonking

💅 MPI_Mrecv — the Open MPI glow-up ✨

okay bestie, we're in the Open MPI manual, section 3, and today's main character is MPI_Mrecv. Blocking receive for a matched message. Yes, matched. As in, somebody already did the probing for you and now you're cashing in. iykyk 🎀

✨ NAME ✨

MPI_Mrecv — Blocking receive for a matched message

no cap, that's the whole vibe. 💖

🦋 SYNTAX 🦋

C Syntax

#include <mpi.h>

int MPI_Mrecv(void *buf, int count, MPI_Datatype type,
     MPI_Message *message, MPI_Status *status)

Fortran Syntax

USE MPI
! or the older form: INCLUDE 'mpif.h'
MPI_MRECV(BUF, COUNT, DATATYPE, MESSAGE, STATUS, IERROR)
     <type>  BUF(*)
     INTEGER COUNT, DATATYPE, MESSAGE
     INTEGER STATUS(MPI_STATUS_SIZE), IERROR

Fortran 2008 Syntax

USE mpi_f08
MPI_Mrecv(buf, count, datatype, message, status, ierror)
     TYPE(*), DIMENSION(..) :: buf
     INTEGER, INTENT(IN) :: count
     TYPE(MPI_Datatype), INTENT(IN) :: datatype
     TYPE(MPI_Message), INTENT(INOUT) :: message
     TYPE(MPI_Status) :: status
     INTEGER, OPTIONAL, INTENT(OUT) :: ierror

🌸 INPUT PARAMETERS 🌸

  • count — how many elements you're receiving. Nonnegative integer, so please don't be out here passing negative numbers, that's not the vibe. 🙈
  • datatype — the datatype of each element of the send buffer. It's a handle. ✨
  • message — the message. Handle. The whole point of the function, honestly. 👑

💜 OUTPUT PARAMETERS 💜

  • buf — initial address of the receive buffer. It's a choice, so pick your fighter. 🫶
  • status — the status object. Status. Yeah. 📊
  • ierror — Fortran only, bestie: error status, an integer. 🧚

🔥 DESCRIPTION 🔥

so the way that MPI_Mrecv and MPI_Imrecv work is: they receive messages that have previously been matched by a matching probe. The probe did the flirting, this is the actual date. 💅

If MPI_Mrecv gets called with MPI_MESSAGE_NULL as the message argument, it returns immediately, with the status object set to source = MPI_PROC_NULL, tag = MPI_ANY_TAG, and count = 0 — literally as if a receive from MPI_PROC_NULL was issued. iconic behavior, honestly.

And if your application doesn't need to examine the status field? Bestie, save those resources. Use the predefined constant MPI_STATUS_IGNORE as a special value for the status argument. obsessed with the efficiency. ✨

💀 ERRORS 💀

ngl almost all MPI routines return an error value: C routines hand it back as the return result of the function, and Fortran routines put it in the last argument. fr fr.

Before the error value is returned, the current MPI error handler associated with the communication object — like a communicator, window, or file — gets 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. And when MPI_COMM_SELF is not initialized — that's 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 the info key to MPI_Comm_spawn / MPI_Comm_spawn_multiple. And 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. periodt. 💅

the three predefined error handlers, bestie 👑

Open MPI includes three predefined error handlers that can be used:

  • MPI_ERRORS_ARE_FATAL — Causes the program to abort all connected MPI processes. yes, ALL of them. dramatic but effective. 💀
  • 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. polite king behavior. 🫶

build your own error handler, DIY queen 🎀

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, at all. 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. 📚

the status field tea ☕

Note that per the "Return Status" section in the "Point-to-Point Communication" chapter in the MPI Standard (https://www.mpi-forum.org/docs/), MPI errors on messages received by MPI_Mrecv do not set the status.MPI_ERROR field in the returned status. The error code is always passed to the back-end error handler and may be passed back to the caller through the return value of MPI_Mrecv if the back-end error handler returns it. The pre-defined MPI error handler MPI_ERRORS_RETURN exhibits this behavior, for example. lowkey important, highkey giving "read it twice". 👀

See also: 🌟

  • MPI_Mprobe
  • MPI_Improbe
  • MPI_Probe
  • MPI_Iprobe
  • MPI_Imrecv
  • MPI_Cancel

2003-2026, The Open MPI Community

and that's the whole page, bestie 🩷 this was MPI_Mrecv(3) from the Open MPI manual, and the footer energy is: dated Sep 10, 2026, straight out of the Open MPI source, version 3 of the manual just like the header said at the very top. slay, you read the whole thing, go receive some matched messages responsibly ✨💅🦋

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