MPI_ISSEND(3)

💌 MPI_ISSEND(3) — Open MPI 💌

okay bestie, this is the Open MPI manual page for MPI_Issend — the nonblocking synchronous send that’s lowkey iconic for keeping your MPI code moving. 💅✨

✨ SYNTAX ✨

💻 C Syntax 💻

          #include <mpi.h>

          int MPI_Issend(const void *buf, int count, MPI_Datatype datatype, int dest,
               int tag, MPI_Comm comm, MPI_Request *request)

🧚 Fortran Syntax 🧚

          USE MPI
          ! or the older form: INCLUDE 'mpif.h'
          MPI_ISSEND(BUF, COUNT, DATATYPE, DEST, TAG, COMM, REQUEST, IERROR)
               <type>  BUF(*)
               INTEGER COUNT, DATATYPE, DEST, TAG, COMM, REQUEST, IERROR

🦋 Fortran 2008 Syntax 🦋

          USE mpi_f08
          MPI_Issend(buf, count, datatype, dest, tag, comm, request, ierror)
               TYPE(*), DIMENSION(..), INTENT(IN), ASYNCHRONOUS :: buf
               INTEGER, INTENT(IN) :: count, dest, tag
               TYPE(MPI_Datatype), INTENT(IN) :: datatype
               TYPE(MPI_Comm), INTENT(IN) :: comm
               TYPE(MPI_Request), INTENT(OUT) :: request
               INTEGER, OPTIONAL, INTENT(OUT) :: ierror

📥 INPUT PARAMETERS 📥

• buf — Initial address of send buffer (choice). This is where the data lives, bestie. 🎀
• count — Number of elements in send buffer (integer). Count ’em.
• datatype — Datatype of each send buffer element (handle).
• dest — Rank of destination (integer). Who’s getting the message? 👑
• tag — Message tag (integer). Label your vibe.
• comm — Communicator (handle).

📤 OUTPUT PARAMETERS 📤

• request — Communication request (handle). Hold onto this, iykyk. 🫶
• ierror — Fortran only: Error status (integer).

🌸 DESCRIPTION 🌸

Starts a synchronous mode, nonblocking send. Periodt.

Nonblocking calls allocate a communication request object and associate it with the request handle — that’s the request argument. You can use that request later to query the status of the communication or wait for its completion. Very main character energy. ✨

A nonblocking send call indicates that the system may start copying data out of the send buffer.

🚨 bestie, listen: the sender should not modify any part of the send buffer after a nonblocking send operation is called, until the send completes. No cap. 💀

🚨 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.

👀 SEE ALSO 👀

• MPI_Ssend

📜 COPYRIGHT 📜

2003-2026, The Open MPI Community

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💖 That’s a wrap, bestie! Source/version: Open MPI · date: Sep 11, 2026 · © 2003-2026, The Open MPI Community. Byeeee! 🫶✨