MPI_TESTSOME(3)

📦
version 5.0.11 · 17 versions
, in arch rolling

💅 MPI_TESTSOME(3) — Open MPI, but make it make sense 🫶

okay so bestie, welcome to MPI_Testsome — the Open MPI page for checking on a whole lil list of communications you already kicked off, and finding out which ones finished. No blocking, no waiting around, she's a check and go icon. ✨

✨ SYNTAX ✨

🧵 C Syntax

#include <mpi.h>

int MPI_Testsome(int incount, MPI_Request array_of_requests[],
     int *outcount, int array_of_indices[],
     MPI_Status array_of_statuses[])

🧚 Fortran Syntax

USE MPI
! or the older form: INCLUDE 'mpif.h'
MPI_TESTSOME(INCOUNT, ARRAY_OF_REQUESTS, OUTCOUNT,
             ARRAY_OF_INDICES, ARRAY_OF_STATUSES, IERROR)
     INTEGER INCOUNT, ARRAY_OF_REQUESTS(*)
     INTEGER OUTCOUNT, ARRAY_OF_INDICES(*)
     INTEGER ARRAY_OF_STATUSES(MPI_STATUS_SIZE,*), IERROR

🌈 Fortran 2008 Syntax

USE mpi_f08
MPI_Testsome(incount, array_of_requests, outcount, array_of_indices,
             array_of_statuses, ierror)
     INTEGER, INTENT(IN) :: incount
     TYPE(MPI_Request), INTENT(INOUT) :: array_of_requests(incount)
     INTEGER, INTENT(OUT) :: outcount, array_of_indices(*)
     TYPE(MPI_Status) :: array_of_statuses(*)
     INTEGER, OPTIONAL, INTENT(OUT) :: ierror

🌸 INPUT PARAMETERS 🌸

  • incount — the length of array_of_requests (that's an integer bestie).
  • array_of_requests — the actual array of requests (array of handles). your lil roster of pending stuff 👑

🎀 OUTPUT PARAMETERS 🎀

  • outcount — how many of your requests completed (integer).
  • array_of_indices — an array of integers holding the indices of the operations that completed.
  • array_of_statuses — an array of status objects, one for each completed operation (array of status).
  • ierror — Fortran only, the error status (integer).

🦋 DESCRIPTION 🦋

okay so honestly? this one is MPI_Waitsome's younger, more impatient sister — she behaves just like MPI_Waitsome except that it returns immediately. no blocking, we love a low-maintenance queen 💅

She returns in outcount the number of requests from the list array_of_requests that have completed. Then she drops into the first outcount locations of the array array_of_indices the indices of those operations — the index is within the array array_of_requests, and plot twist: that array is indexed from 0 in C and from 1 in Fortran. 🙈

Then in the first outcount locations of the array array_of_status she returns the status for those completed operations. And if a request that completed was allocated by a nonblocking communication call, then it gets deallocated, and the associated handle is set to MPI_REQUEST_NULL. clean up, clean up 🧹

If no operation has completed, it returns outcount = 0. If there is no active handle in the list at all, it returns outcount = MPI_UNDEFINED.

MPI_Testsome is a local operation, and it returns immediately — versus MPI_Waitsome, which blocks until a communication completes if it was passed a list containing at least one active handle. Both calls fulfill a fairness requirement, and this part is important so listen up: if a request for a receive repeatedly appears in a list of requests passed to MPI_Waitsome or MPI_Testsome, and a matching send has been posted, then the receive will eventually succeed unless the send is satisfied by another receive; send requests also fulfill this fairness requirement. periodt. ⭐

Errors that occur during the execution of MPI_Testsome are handled as for MPI_Waitsome.

And a cute lil resource-saver: if your application does not need to examine the array_of_statuses field, you can save resources by using the predefined constant MPI_STATUSES_IGNORE — it can be used as a special value for the array_of_statuses argument. 🍓

💜 NOTES 💜

Using MPI_Testsome is likely to be more efficient than using MPI_Testany. Why? The former returns information on all completed communications; with the latter, a new call is required for each communication that completes. she's giving efficiency main character energy 👑

A server with multiple clients can use MPI_Waitsome so as not to starve any client. The setup: clients send messages to the server with service requests. The server calls MPI_Waitsome with one receive request for each client, then handles all receives that have completed. But if a call to MPI_Waitany is used instead, then one client could starve while requests from another client always sneak in first. 😭 not the starvation!

💀 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 you can use:

  • 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
ngl bestie, 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.

Now here's the tea for each invocation of MPI_Testsome: if one or more requests generate an MPI error, only the first MPI request that caused an error will be passed to its corresponding error handler. No other error handlers will be invoked (even if multiple requests generated errors). However, all requests that generate an error will have a relevant error code set in the corresponding status.MPI_ERROR field (unless MPI_STATUSES_IGNORE was used). 🙈

If the invoked error handler allows MPI_Testsome to return to the caller, the value MPI_ERR_IN_STATUS will be returned in the C and Fortran bindings.

👑 SEE ALSO 👑

  • MPI_Comm_set_errhandler
  • MPI_File_set_errhandler
  • MPI_Test
  • MPI_Testall
  • MPI_Testany
  • MPI_Wait
  • MPI_Waitall
  • MPI_Waitany
  • MPI_Waitsome
  • MPI_Win_set_errhandler

2003-2026, The Open MPI Community

and that's the whole page, bestie 🎀 she's dated Sep 11, 2026, she ships as part of Open MPI, and she's filed under MPI_TESTSOME(3) — go forth and test some requests, iykyk 💖✨

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