MPI_TEST(3)

📦

version 5.0.10 · 7 versions

💖 MPI_TEST(3) — an Open MPI moment 💖

okay bestie, gather round, because we're about to talk about the vibe-check function for nonblocking sends and receives. This is the Open MPI manual, section 3, and it's giving glow-up. 🦋

🌟 NAME

MPI_Test — checks whether one specific send or receive has finished yet. That's it, that's the whole job. 👑

✨ SYNTAX

🍓 C Syntax

#include <mpi.h>

int MPI_Test(MPI_Request *request, int *flag, MPI_Status *status)

🍓 Fortran Syntax

USE MPI
! or the older form: INCLUDE 'mpif.h'
MPI_TEST(REQUEST, FLAG, STATUS, IERROR)
     LOGICAL FLAG
     INTEGER REQUEST, STATUS(MPI_STATUS_SIZE), IERROR

🍓 Fortran 2008 Syntax

USE mpi_f08
MPI_Test(request, flag, status, ierror)
     TYPE(MPI_Request), INTENT(INOUT) :: request
     LOGICAL, INTENT(OUT) :: flag
     TYPE(MPI_Status) :: status
     INTEGER, OPTIONAL, INTENT(OUT) :: ierror

📥 INPUT PARAMETER

request — the communication request handle. It's the little ticket that says "hey, this operation exists." (handle) 🎀

📤 OUTPUT PARAMETERS

flag — true if the operation completed, false if not. The emotional support boolean. (logical) ✅
status — the status object, full of gossip about the completed operation. (status) 📋
ierror — Fortran only: the error status. (integer) 🚨

💅 DESCRIPTION

So when you call MPI_Test, it returns flag = true if the operation identified by request is complete. And in that case the status object gets set to contain info on the completed operation. And if that communication object was created by a nonblocking send or receive, it gets deallocated and the request handle is set to MPI_REQUEST_NULL. Cleanup queen behavior, honestly. 🧹✨

Otherwise it returns flag = false, and in that case the value of the status object is undefined — like, do not go reading it, it's not your business yet. And important: MPI_Test is a local operation. No waiting on anyone else, no blocking, just a quick peek. 👀

The return status object for a receive operation carries information you can access as described in the "Return Status" subsection of the "Point-to-Point Communication" chapter in the MPI Standard — it lives over at https://www.mpi-forum.org/docs/. 📚

The status object for a send operation carries information that you can access by calling MPI_Test_cancelled (see the "Probe and Cancel" section of the MPI Standard, same link: https://www.mpi-forum.org/docs/). 🔍

If your app doesn't actually need to look at the status field, you can save resources by using the predefined constant MPI_STATUS_IGNORE as a special value for the status argument. Minimal effort, maximum slay. 💅

And here's a fun one: you're allowed to call MPI_Test with a null or inactive request argument. In that case the operation returns with flag = true and an empty status. Free win, no cap. 🎉

Also, the functions MPI_Wait (#mpi-wait) and MPI_Test can be used to complete both sends and receives. Equal opportunity completer. 🤝

📝 NOTES

Using the nonblocking MPI_Test call lets you schedule alternative activities inside a single thread of execution. Basically: an event-driven thread scheduler can be emulated with periodic calls to MPI_Test. DIY scheduler era, we love to see it. 🧠✨

🚨 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. So yes, check your values, bestie. 👀

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) / MPI_Init_thread (#mpi-init-thread), after MPI_Finalize (#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 (#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) / MPI_Comm_spawn_multiple (#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 you can use: 👇

MPI_ERRORS_ARE_FATAL — causes the program to abort all connected MPI processes. Dramatic, but make it final. 💀
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 (#mpi-abort) was called on that communicator. If called on a window or file, it acts as if MPI_Abort (#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 and communicative, we stan. 📨

MPI applications can also implement their own error handlers by calling: 🛠️

MPI_Comm_create_errhandler (#mpi-comm-create-errhandler) then MPI_Comm_set_errhandler (#mpi-comm-set-errhandler)
MPI_File_create_errhandler (#mpi-file-create-errhandler) then MPI_File_set_errhandler (#mpi-file-set-errhandler)
MPI_Session_create_errhandler (#mpi-session-create-errhandler) then MPI_Session_set_errhandler (#mpi-session-set-errhandler) or at MPI_Session_init (#mpi-session-init)
MPI_Win_create_errhandler (#mpi-win-create-errhandler) then MPI_Win_set_errhandler (#mpi-win-set-errhandler)

⚠️ Note that MPI does not guarantee that an MPI program can continue past an error. So don't just assume you get to keep going, bestie. 🫠

See the MPI man page (#open-mpi) for a full list of MPI error codes (#open-mpi-errors). 📖

See the Error Handling section of the MPI-3.1 standard for more information. 🔎

Also 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 requests passed to MPI_Test 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_Test if the back-end error handler returns it. The pre-defined MPI error handler MPI_ERRORS_RETURN exhibits this behavior, for example. 🧵

👑 Copyright

2003-2026, The Open MPI Community 🫶

and that's the whole page, bestie!! no crumbs left. this was the MPI_TEST(3) page from Open MPI (manual section 3), dated Sep 10, 2026, copyright 2003-2026, The Open MPI Community — go test your requests and stay iconic. 💖🌈✨

📦 where this page comes from

ubuntu stonking: openmpi-doc 5.0.10-6 · other
💖 girlified by deepseek-ai/DeepSeek-V4.1-Flash on 2026-11-03: a language model's rewrite of the original, under its terms