MPI_T_event_handle_alloc(3)

💖 MPI_T_event_handle_alloc(3) 💖

okay bestie so this is a page from the MPI manual, section 3, and today's main character is MPI_T_event_handle_alloc. it's giving ✨registration✨ energy and honestly? we're obsessed.

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🌸 NAME 🌸

MPI_T_event_handle_alloc — creates a registration handle for the event type identified by event_index 🎀

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✨ SYNOPSIS ✨

int MPI_T_event_handle_alloc(int event_index, void *obj_handle, MPI_Info info,
       MPI_T_event_registration *event_registration)

like. look at those parameters. gorgeous. impeccable. let's get into it 💅

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🫶 INPUT PARAMETERS 🫶

• event_index — the index of the event type that we're allocating a registration handle for. it's an integer, no cap. 🔢
• obj_handle — a reference to a handle of the mpi object that this event is supposed to be bound to. it's a pointer. 🪢
• info — an info object, and yes it's a handle. 📋

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👑 OUTPUT PARAMETERS 👑

• event_registration — ta-da!! ✨ the event registration, which is (you guessed it) a handle. this is the whole point of the function bestie. 🌟

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🧚 THREAD AND INTERRUPT SAFETY 🧚

good news first: this routine is thread-safe. that means multiple threads can use it at the same time and you do not need to bring your own user-provided thread locks. slay. 🎉

but. and there's always a but. 😭 this routine is not interrupt safe. the reason is typically that it uses memory allocation routines like malloc, or other non-MPICH runtime routines, which are themselves not interrupt-safe. so like… interrupt it at your own risk, fr fr. 💀

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💜 ERRORS 💜

okay so real talk. every MPI routine except MPI_Wtime and MPI_Wtick returns an error value. C routines hand it back as the value of the function; Fortran routines put it in the last argument. 🫡

before that value comes back to you, the current MPI error handler gets called. by default, that error handler aborts the MPI job. like, whole job. gone. 🙈

you can change the error handler with:

• MPI_Comm_set_errhandler (for communicators)
• MPI_File_set_errhandler (for files)
• MPI_Win_set_errhandler (for RMA windows)

there's also the MPI-1 routine MPI_Errhandler_set, which you may use, but its use is deprecated. lowkey don't. 🚫

the predefined error handler MPI_ERRORS_RETURN may be used to cause error values to be returned instead. and note: MPI does not guarantee that an MPI program can continue past an error; however, MPI implementations will attempt to continue whenever possible. so… vibes may vary. 🌈

here's the error code lineup:

• MPI_SUCCESS — no error; the MPI routine completed successfully. 🥳
• MPI_ERR_INFO — invalid Info. 📛
• MPI_T_ERR_INVALID — invalid use of the interface, or bad parameter value(s). 🚩
• MPI_T_ERR_INVALID_INDEX — the index is invalid or has been deleted. 🗑️
• MPI_T_ERR_NOT_INITIALIZED — the MPI tool information interface is not initialized. 😴
• MPI_ERR_OTHER — other error; use MPI_Error_string to get more information about this error code. 🔍

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reminder bestie: MPI_T_ERR_NOT_INITIALIZED exists for a reason — if the MPI tool information interface isn't initialized, this is not the moment. 💅

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and that's the whole page, periodt. 🎀 this little masterpiece comes from the MPI source and it's dated 4/10/2026. mwah, take care of her, she's iconic. 💖🦋🌸