MPI_TEST(3)					     Open MPI					       MPI_TEST(3)

MPI_Test — Tests for the completion of a specific send or receive.

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: Communication request (handle).

OUTPUT PARAMETERS
       • flag: True if operation completed (logical).

       • status: Status object (status).

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

DESCRIPTION
       A  call to MPI_Test returns flag = true if the operation identified by request is complete. In such a case,
       the status object is set to contain information on the completed operation; if the communication object was
       created by a nonblocking send or receive, then  it  is  deallocated  and	 the  request  handle  is  set	to
       MPI_REQUEST_NULL. The call returns flag = false, otherwise. In this case, the value of the status object is
       undefined. MPI_Test is a local operation.

       The  return  status object for a receive operation carries information that can be accessed as described in
       the “Return Status” subsection of the “Point-to-Point Communication” chapter in the MPI Standard	 <https://
       www.mpi-forum.org/docs/>.  The  status object for a send operation carries information that can be accessed
       by a call to MPI_Test_cancelled <#mpi-test-cancelled> (see the  “Probe  and  Cancel”  section  of  the  MPI
       Standard <https://www.mpi-forum.org/docs/>).

       If  your	 application  does  not	 need  to  examine  the	 status field, you can save resources by using the
       predefined constant MPI_STATUS_IGNORE as a special value for the status argument.

       One is allowed to call MPI_Test with a null or inactive request argument. In  such  a  case  the	 operation
       returns with flag = true and empty status.

       The functions MPI_Wait <#mpi-wait> and MPI_Test can be used to complete both sends and receives.

NOTES
       The use of the nonblocking MPI_Test call allows the user to schedule alternative activities within a single
       thread of execution. An event-driven thread scheduler can be emulated with periodic calls to MPI_Test.

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.

       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.

       See also:

	  • MPI_Comm_set_errhandler <#mpi-comm-set-errhandler>

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

	  • MPI_Testall <#mpi-testall>

	  • MPI_Testany <#mpi-testany>

	  • MPI_Testsome <#mpi-testsome>

	  • 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_TEST(3)
