--- name: "MPI_Imrecv" section: "3" platform: "linux" package: "openmpi" version: "5.0.11-1" release: "Arch Linux 2026-11-01" platforms: ["linux"] url: "https://new.carta.tech/MPI_Imrecv" --- # MPI\_Imrecv(3) *MPI\_Imrecv* — Non-blocking receive for a matched message ## SYNTAX ### C Syntax ``` #include int MPI_Imrecv(void *buf, int count, MPI_Datatype type, MPI_Message *message, MPI_Request *request) ``` ### Fortran Syntax ``` USE MPI ! or the older form: INCLUDE 'mpif.h' MPI_IMRECV(BUF, COUNT, DATATYPE, MESSAGE, REQUEST, IERROR) BUF(*) INTEGER COUNT, DATATYPE, MESSAGE, REQUEST, IERROR ``` ### Fortran 2008 Syntax ``` USE mpi_f08 MPI_Imrecv(buf, count, datatype, message, request, ierror) TYPE(*), DIMENSION(..), ASYNCHRONOUS :: buf INTEGER, INTENT(IN) :: count TYPE(MPI_Datatype), INTENT(IN) :: datatype TYPE(MPI_Message), INTENT(INOUT) :: message TYPE(MPI_Request), INTENT(OUT) :: request INTEGER, OPTIONAL, INTENT(OUT) :: ierror ``` ## INPUT PARAMETERS - • **count**: Number of elements to receive (nonnegative integer). - • **datatype**: Datatype of each send buffer element (handle). - • **message**: Message (handle). ## OUTPUT PARAMETERS - • **buf**: Initial address of receive buffer (choice). - • **request**: Request (handle). - • **ierror**: Fortran only: Error status (integer). ## DESCRIPTION The functions *MPI\_Mrecv* and *MPI\_Imrecv* receive messages that have been previously matched by a matching probe. The *request* returned from *MPI\_Imrecv* can be used with any of the *MPI\_Test* and *MPI\_Wait* variants, like any non-blocking receive request. If *MPI\_Imrecv* is called with **MPI\_MESSAGE\_NULL** as the message argument, a call to one of the *MPI\_Test* or *MPI\_Wait* variants will return immediately with the *status* object set to *source* = **MPI\_PROC\_NULL**, *tag* = **MPI\_ANY\_TAG**, and *count* = 0, as if a receive from **MPI\_PROC\_NULL** was issued. If reception of a matched message is started with *MPI\_Imrecv*, then it is possible to cancel the returned request with *MPI\_Cancel*. If *MPI\_Cancel* succeeds, the matched message must be found by a subsequent message probe (*MPI\_Probe*, *MPI\_Iprobe*, *MPI\_Mprobe*, or *MPI\_Improbe*), received by a subsequent receive operation or canceled by the sender. Note, however, that is it possible for the cancellation of operations initiated with *MPI\_Imrecv* to fail. An example of a failing case is when canceling the matched message receive would violate MPI message ordering rules (e.g., if another message matching the same message signature has matched — and possibly received — before this *MPI\_Imrecv* is canceled). 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\_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 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* 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* 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. Note that per the “Return Status” section in the “Point-to-Point Communication” chapter in the *MPI Standard*, MPI errors on messages received by *MPI\_Imrecv* 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\_Imrecv* 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\_Mprobe* - • *MPI\_Improbe* - • *MPI\_Probe* - • *MPI\_Iprobe* - • *MPI\_Imrecv* - • *MPI\_Cancel* ## COPYRIGHT 2003-2026, The Open MPI Community