MPI_TESTSOME(3)					     Open MPI					   MPI_TESTSOME(3)

MPI_Testsome — Tests for completion of one or more previously initiated communications in a list.

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: Length of array_of_requests (integer).

       • array_of_requests: Array of requests (array of handles).

OUTPUT PARAMETERS
       • outcount: Number of completed requests (integer).

       • array_of_indices: Array of indices of operations that completed (array of integers).

       • array_of_statuses: Array of status objects for operations that completed (array of status).

       • ierror: Fortran only: Error status (integer).

DESCRIPTION
       Behaves like MPI_Waitsome <#mpi-waitsome>, except that it returns immediately.

       Returns	in outcount the number of requests from the list array_of_requests that have completed. Returns in
       the first outcount locations of the array array_of_indices the indices of these	operations  (index  within
       the  array array_of_requests; the array is indexed from 0 in C and from 1 in Fortran). Returns in the first
       outcount locations of the array array_of_status the status for these completed  operations.  If	a  request
       that  completed	was  allocated	by  a  nonblocking  communication  call,  then	it is deallocated, and the
       associated handle is set to MPI_REQUEST_NULL.

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

       MPI_Testsome is a local operation, which returns immediately, whereas MPI_Waitsome  <#mpi-waitsome>  blocks
       until  a	 communication	completes,  if it was passed a list that contains at least one active handle. Both
       calls fulfill a fairness requirement: If a request for a receive repeatedly appears in a list  of  requests
       passed  to  MPI_Waitsome	 <#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.

       Errors that occur during the execution of MPI_Testsome are handled as for MPI_Waitsome <#mpi-waitsome>.

       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  can  be	used  as a special value for the array_of_statuses
       argument.

NOTES
       The use of MPI_Testsome is likely to be more efficient than the	use  of	 MPI_Testany  <#mpi-testany>.  The
       former  returns	information  on	 all completed communications; with the latter, a new call is required for
       each communication that completes.

       A server with multiple clients can use MPI_Waitsome <#mpi-waitsome> so as not to starve any client. Clients
       send messages to the server with service requests.  The server calls MPI_Waitsome <#mpi-waitsome> with  one
       receive request for each client, then handles all receives that have completed. If a call to MPI_Waitany <#
       mpi-waitany>  is used instead, then one client could starve while requests from another client always sneak
       in first.

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>/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 that can be used:

       • 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 <#mpi-abort> was called on that communicator. If called
	 on a window or file, 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, 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	 <#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.

       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.

       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-comm-set-errhandler>

	  • MPI_File_set_errhandler <#mpi-file-set-errhandler>

	  • MPI_Test <#mpi-test>

	  • MPI_Testall <#mpi-testall>

	  • MPI_Testany <#mpi-testany>

	  • MPI_Wait <#mpi-wait>

	  • MPI_Waitall <#mpi-waitall>

	  • MPI_Waitany <#mpi-waitany>

	  • MPI_Waitsome <#mpi-waitsome>

	  • MPI_Win_set_errhandler <#mpi-win-set-errhandler>

Copyright
       2003-2026, The Open MPI Community

						   Mar 05, 2026					   MPI_TESTSOME(3)
