MPI_T_category_get_num_events(3)

✨ NAME ✨

MPI_T_category_get_num_events — bestie, this one tells you how many event types are chillin' inside the category you just queried. That's it, that's the whole job. 💖

(also hi, this is the MPI manual, page MPI_T_category_get_num_events(3), and we're about to get you fluent in it 🫶)

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🌸 SYNOPSIS 🌸

int MPI_T_category_get_num_events(int cat_index, int *num_events)

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🎀 INPUT PARAMETERS 🎀

• cat_index — the index of the category you wanna query, an integer obvi. It's giving "which one tho" energy 🦋

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💅 OUTPUT PARAMETERS 💅

• num_events — out comes the number of event types in that category (also an integer, no cap) ✨

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🧚 THREAD AND INTERRUPT SAFETY 🧚

Okay so the 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 thread locks. She handles herself. 👑

But — and I need you to hear this — she is not interrupt safe. 😭 Typically that's because of memory allocation routines like malloc or other non-MPICH runtime routines, which are themselves not interrupt-safe. So like, she's fine in the group chat but don't jump-scare her mid-allocation, periodt.

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💀 ERRORS 💀

So every MPI routine (except MPI_Wtime and MPI_Wtick, the lucky ones) is gonna hand you back an error value. In C it's the return value of the function; in Fortran it's the last argument. And before that value comes back, the current MPI error handler gets called.

By default, that error handler aborts the whole MPI job. 💀 Yes really. It's dramatic like that.

You can swap 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, and you may use it, but its use is deprecated — so like, she's still around but we don't stan. 🙈

If you'd rather get error values returned to you instead of the job getting nuked, use the predefined error handler MPI_ERRORS_RETURN. 🫶

Heads up: MPI does not guarantee that an MPI program can keep going past an error. However, MPI implementations will attempt to continue whenever possible. So it's a vibe check, not a promise. 🌈

Now the actual error codes, our little roster:

• MPI_SUCCESS — no error, the routine completed successfully. The dream. ✨
• MPI_T_ERR_INVALID — invalid use of the interface or bad parameter value(s). Rude of you tbh.
• MPI_T_ERR_INVALID_INDEX — the index is invalid or has been deleted. She's not here anymore, bestie. 👻
• MPI_T_ERR_NOT_INITIALIZED — the MPI tool information interface is not initialized. You gotta wake her up first 😭
• MPI_ERR_OTHER — other error; use MPI_Error_string to get more info about this error code. The catch-all, the mystery box 🎁

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🦋 SEE ALSO 🦋

Nothing else listed on this page, so I guess it's just us two and this function. Iconic honestly. 💜

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kisses bestie, you're officially fluent in counting event types 🎀🌸💅

This was the MPI manual, page MPI_T_category_get_num_events(3), dated 4/10/2026 — go forth and query those categories, you absolute main character 👑✨