MPI_RECV(3)					     Open MPI					       MPI_RECV(3)

MPI_Recv — Performs a standard-mode blocking receive.

SYNTAX
   C Syntax
	  #include <mpi.h>

	  int MPI_Recv(void *buf, int count, MPI_Datatype datatype,
	       int source, int tag, MPI_Comm comm, MPI_Status *status)

   Fortran Syntax
	  USE MPI
	  ! or the older form: INCLUDE 'mpif.h'
	  MPI_RECV(BUF, COUNT, DATATYPE, SOURCE, TAG, COMM, STATUS, IERROR)
	       <type>  BUF(*)
	       INTEGER COUNT, DATATYPE, SOURCE, TAG, COMM
	       INTEGER STATUS(MPI_STATUS_SIZE), IERROR

   Fortran 2008 Syntax
	  USE mpi_f08
	  MPI_Recv(buf, count, datatype, source, tag, comm, status, ierror)
	       TYPE(*), DIMENSION(..) :: buf
	       INTEGER, INTENT(IN) :: count, source, tag
	       TYPE(MPI_Datatype), INTENT(IN) :: datatype
	       TYPE(MPI_Comm), INTENT(IN) :: comm
	       TYPE(MPI_Status) :: status
	       INTEGER, OPTIONAL, INTENT(OUT) :: ierror

INPUT PARAMETERS
       • count: Maximum number of elements to receive (integer).

       • datatype: Datatype of each receive buffer entry (handle).

       • source: Rank of source (integer).

       • tag: Message tag (integer).

       • comm: Communicator (handle).

OUTPUT PARAMETERS
       • buf: Initial address of receive buffer (choice).

       • status: Status object (status).

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

DESCRIPTION
       This  basic receive operation, MPI_Recv, is blocking: it returns only after the receive buffer contains the
       newly received message. A receive can complete before the matching send has completed (of  course,  it  can
       complete only after the matching send has started).

       The  blocking semantics of this call are described in the “Communication Modes” section of the MPI Standard
       <https://www.mpi-forum.org/docs/>.

       The receive buffer contains a number (defined by the value of count) of	consecutive  elements.	The  first
       element	in  the set of elements is located at address_buf. The type of each of these elements is specified
       by datatype.

       The length of the received message must be less than or equal to the  length  of	 the  receive  buffer.	An
       MPI_ERR_TRUNCATE is returned upon the overflow condition.

       If  a  message  that  is	 shorter  than the length of the receive buffer arrives, then only those locations
       corresponding to the (shorter) received message are modified.

NOTES
       The count argument indicates the maximum number of entries of type datatype  that  can  be  received  in	 a
       message.	 Once  a  message  is  received,  use the MPI_Get_count <#mpi-get-count> function to determine the
       actual number of entries within that message.

       To receive messages of unknown length, use the MPI_Probe <#mpi-probe> function.	For more information about
       MPI_Probe <#mpi-probe> and MPI_Cancel <#mpi-cancel>, see their respective man  pages  and  the  “Probe  and
       Cancel” section of the MPI Standard <https://www.mpi-forum.org/docs/>.

       A  message  can be received by a receive operation only if it is addressed to the receiving process, and if
       its source, tag, and communicator (comm) values match the source, tag, and comm	values	specified  by  the
       receive	operation.  The	 receive  operation may specify a wildcard value for source and/or tag, indicating
       that any source and/or tag are acceptable. The wildcard value for source is source =  MPI_ANY_SOURCE.   The
       wildcard	 value	for  tag  is  tag  =  MPI_ANY_TAG. There is no wildcard value for comm. The scope of these
       wildcards is limited to the processes in the group of the specified communicator.

       The message tag is specified by the tag argument of the receive operation.

       The argument source, if different from MPI_ANY_SOURCE, is specified as a	 rank  within  the  process  group
       associated  with	 that same communicator (remote process group, for intercommunicators). Thus, the range of
       valid values for the source argument is {0,…,n-1} {MPI_ANY_SOURCE}, where n is the number of  processes	in
       this group.

       Note  the  asymmetry  between  send and receive operations: A receive operation may accept messages from an
       arbitrary sender; on the other hand, a send operation must specify a unique receiver. This matches a “push”
       communication mechanism, where data transfer is effected by the sender (rather  than  a	“pull”	mechanism,
       where data transfer is effected by the receiver).

       Source  =  destination  is  allowed,  that  is,	a process can send a message to itself. However, it is not
       recommended for a process to send messages to  itself  using  the  blocking  send  and  receive	operations
       described  above,  since this may lead to deadlock.  See the “Semantics of Point-to-Point Communication” of
       the MPI Standard <https://www.mpi-forum.org/docs/> for more details.

       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.

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  messages  received	by  MPI_Recv  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_Recv  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_Irecv <#mpi-irecv>

	  • MPI_Probe <#mpi-probe>

Copyright
       2003-2026, The Open MPI Community

						   Mar 05, 2026					       MPI_RECV(3)
