MPI_START(3)

💅 MPI_START(3) — like, the Open MPI glow-up ✨

okay bestie, welcome to MPI_Start from Open MPI — she's the one who actually launches your persistent requests. Buckle up, this is gonna be iconic 🎀

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🌸 SYNTAX 🌸

💖 C Syntax

#include <mpi.h>

int MPI_Start(MPI_Request *request)

💖 Fortran Syntax

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

💖 Fortran 2008 Syntax

USE mpi_f08
MPI_Start(request, ierror)
     TYPE(MPI_Request), INTENT(INOUT) :: request
     INTEGER, OPTIONAL, INTENT(OUT) :: ierror

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🌈 INPUT PARAMETER 🌈

• request — your communication request (a handle, bestie 💅). That's the whole vibe.

🌟 OUTPUT PARAMETER 🌟

• ierror — Fortran only, girlie: the error status, as an integer. ✨

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🦋 DESCRIPTION 🦋

So here's the tea ☕: a communication — send or receive — that rides on a persistent request gets initiated by MPI_Start. That's her whole job. She starts it. Periodt.

The argument request is a handle that came back from one of the persistent communication-request initialization functions — and yes, we're naming all of them, no skipped members of the group chat:

• MPI_Send_init
• MPI_Bsend_init
• MPI_Ssend_init
• MPI_Rsend_init
• MPI_Recv_init

That associated request should be inactive when you call, and it becomes active the moment the call is made. Glow-up complete 💫

If the request is for a send in ready mode, then a matching receive should be posted before the call is made — like, ahead of time, not fashionably late 🙈. And from the time the call is made until after the operation completes, the communication buffer should not be accessed. Do not touch. Hands off. No cap. 🚫

The call is local, with semantics similar to the nonblocking communication operations — see Section 3.7 in the MPI Standard, "Nonblocking Communication." Basically: a call to MPI_Start with a request created by MPI_Send_init starts a communication in the same manner as a call to MPI_Isend; a call to MPI_Start with a request created by MPI_Bsend_init starts a communication in the same manner as a call to MPI_Ibsend; and so on down the line. Same energy, different wrapper 💅

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💀 ERRORS 💀

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. iykyk.

Before that error value gets returned, the current MPI error handler associated with the communication object (think: 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. And 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. That initial error handler can be changed by calling MPI_Comm_set_errhandler on MPI_COMM_SELF when using the World model, or by 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. 😭

Open MPI ships three predefined error handlers you can use:

• MPI_ERRORS_ARE_FATAL — causes the program to abort all connected MPI processes. dramatic much 💀
• 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. the polite 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, she might just not recover, bestie. don't test her.

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 📚

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👑 SEE ALSO 👑

• MPI_Bsend_init
• MPI_Rsend_init
• MPI_Send_init
• MPI_Ssend_init
• MPI_Recv_init
• MPI_Startall

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🎀 COPYRIGHT 🎀

2003-2026, The Open MPI Community

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and that's the whole page, bestie — written up on Sep 11, 2026, MPI_START(3) from the Open MPI crew 🫶✨ go start something iconic 💅