MPI_GREQUEST_COMPLETE(3)

💅 NAME 💅

MPI_Grequest_complete — bestie, this is the call that tells MPI "yeah, that generalized request? it's done, we finished, periodt." It reports that a generalized request is complete. ✨

Oh and hey — welcome to the Open MPI manual, this is page MPI_GREQUEST_COMPLETE(3), and we're about to make generalized requests make sense, no cap. 🫶

---

🌸 SYNTAX 🌸

⭐ C Syntax

#include <mpi.h>

int MPI_Grequest_complete(MPI_Request request)

💜 Fortran Syntax

USE MPI
! or the older form: INCLUDE 'mpif.h'

MPI_GREQUEST_COMPLETE(REQUEST, IERROR)
    INTEGER REQUEST, IERROR

🦋 Fortran 2008 Syntax

USE mpi_f08

MPI_Grequest_complete(request, ierror)
    TYPE(MPI_Request), INTENT(IN) :: request
    INTEGER, OPTIONAL, INTENT(OUT) :: ierror

---

🎀 INPUT/OUTPUT PARAMETER 🎀

• request — the generalized request handle, aka the little guy you're marking as done. 💖

---

✨ OUTPUT PARAMETER ✨

• ierror — Fortran girlies only: the error status (an integer). 🙈

---

👑 DESCRIPTION 👑

Okay so here's the tea ☕: MPI_Grequest_complete informs MPI that the operations represented by the generalized request request are complete. That's it, that's the job.

The receipts 📜: a call to MPI_Wait(request, status) will return, and a call to MPI_Test(request, flag, status) will return flag=true — but only after a call to MPI_Grequest_complete has declared that these operations are complete. So like, don't expect either of them to pop off before you do this. It's giving "you have to actually tell me you're done." 💀

Now for the serious part, and ngl this one's important 🔥:

MPI imposes no restrictions on the code executed by the callback functions. However — and this is the main character rule — new nonblocking operations should be defined so that the general semantic rules about MPI calls such as MPI_Test, MPI_Request_free, or MPI_Cancel still hold. For example, all these calls are supposed to be local and nonblocking. Therefore, the callback functions query_fn, free_fn, or cancel_fn should invoke blocking MPI communication calls only if the context is such that these calls are guaranteed to return in finite time.

Once MPI_Cancel has been invoked, the canceled operation should complete in finite time, regardless of the state of other processes — the operation has acquired "local" semantics. It should either succeed or fail without side-effects. The user should guarantee these same properties for newly defined operations. 🫡

✨ Translation for the girlies: you're the one who has to keep these promises, bestie. MPI isn't gonna do it for you. 💅

---

💀 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. (Yes, even in Fortran. Especially in Fortran. 😭)

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. 💀 like, everyone. gone.
• 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. The polite one. 🎀

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. Fr fr, don't count on it. 😭

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. ✨

---

🌈 COPYRIGHT 🌈

2003-2026, The Open MPI Community

---

And that's the whole page, bestie — it's giving MPI_GREQUEST_COMPLETE(3) energy from the Open MPI crew, dated Sep 11, 2026. Go forth and complete your generalized requests, icon. 👑💖🦋