MPI_T_cvar_get_index(3)

💖 MPI_T_cvar_get_index(3) 💖

okay bestie, welcome to the MPI manual, page for MPI_T_cvar_get_index 🎀 yes this is a real function name, yes it's a mouthful, no we are not changing it, it's iconic.

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✨ NAME ✨

MPI_T_cvar_get_index — get the index of a control variable 🦋

like, you have a control variable and you want its index? that's the whole job. that's it. that's the girl.

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✨ SYNOPSIS ✨

int MPI_T_cvar_get_index(const char *name, int *cvar_index)

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✨ INPUT PARAMETERS ✨

• name — the name of the control variable, and it's a string bestie 💅

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✨ OUTPUT PARAMETERS ✨

• cvar_index — the index of the control variable, and this one is an integer ✨

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✨ THREAD AND INTERRUPT SAFETY ✨

good news first: this routine is thread-safe 🌈 meaning multiple threads can use it at the same time and you do not need to bring your own thread locks. no user-provided lock drama, we love that for us. 🫶

BUT. 💀 the routine is not interrupt safe. and why, you ask? typically because it uses memory allocation routines like malloc, or other non-MPICH runtime routines, and those are themselves not interrupt-safe. so yeah, not interrupt safe, periodt.

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✨ ERRORS ✨

okay so here's the lore: all MPI routines (except MPI_Wtime and MPI_Wtick) return an error value. C routines return it as the value of the function, and Fortran routines put it in the last argument. before that value comes back to you, the current MPI error handler gets called. and by default? that error handler aborts the MPI job 😭 so yeah, dramatic.

you can change the error handler with MPI_Comm_set_errhandler (for communicators), MPI_File_set_errhandler (for files), and MPI_Win_set_errhandler (for RMA windows). the MPI-1 routine MPI_Errhandler_set may still be used, but its use is deprecated — so like, don't, unless you must, iykyk. 🚫

the predefined error handler MPI_ERRORS_RETURN may be used to make error values get returned instead.

⚠️ note that MPI does not guarantee that an MPI program can continue past an error. however, MPI implementations will attempt to continue whenever possible. so like... fingers crossed? 🤞

the error codes, one by one:

• MPI_SUCCESS — no error; the MPI routine completed successfully. slay. ✨
• MPI_T_ERR_INVALID — invalid use of the interface, or bad parameter value(s). 🙈
• MPI_T_ERR_INVALID_NAME — the variable or category name is invalid. 💀
• 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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and that's the whole page bestie, you ate that 💅✨

sign-off time: this was the MPI manual, page MPI_T_cvar_get_index(3), dated 4/10/2026 🌸 go forth and index your control variables, mwah 💖👑