MPI_T_event_read(3)

💖 MPI_T_event_read — a whole manual page, bestie 💖

okay so this one lives in the MPI manual, section 3 (yes the classic "library calls" girlies), and it's called MPI_T_event_read. It does exactly one thing and it does it cute: copy one single element of event data into a buffer you provide. no cap. one element. that's the whole job. 🎀

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✨ NAME ✨

MPI_T_event_read — Copy one element of event data to a user-specified buffer

like. she is COPYING. ONE. ELEMENT. into a buffer you hand her. lowkey the most straightforward queen in the whole tool interface. 🦋

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🌸 SYNOPSIS 🌸

int MPI_T_event_read(MPI_T_event_instance event_instance, int element_index,
void *buffer)

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💜 INPUT PARAMETERS 💜

• event_instance — the event-instance handle that got handed to your callback function. it's a handle, so treat it like the little VIP wristband it is. 💅
• element_index — an index into the array of datatypes, pointing at the item you wanna query. it's an integer, so yes, counting is involved, we're all doing our best. 😭

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🫶 OUTPUT PARAMETERS 🫶

• buffer — a pointer to a memory location where the item data gets stored. it's a choice type, so the data type is, like, vibes-based. bring your own memory, bestie. ✨

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🧵 THREAD AND INTERRUPT SAFETY 🧵

kay 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 hand-write your own thread locks. it's giving independent queen.

the bad news: it is not interrupt safe. 🙈 typically that's because of memory allocation routines like malloc or other non-MPICH runtime routines that are themselves not interrupt-safe. so like, respect the interrupt boundary, ok? 💀

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🔥 ERRORS 🔥

okay so every single MPI routine (except MPI_Wtime and MPI_Wtick) returns an error value. C routines return it as the value of the function, Fortran routines sneak it into the last argument. 👑

before that value comes back, the current MPI error handler gets called. by default that error handler aborts the entire MPI job, which is. a lot. 😭 the error handler can be swapped out 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 be used, but just so you know, its use is deprecated — old, tired, we're moving on. 🚫 the predefined error handler MPI_ERRORS_RETURN can be used to make error values actually get returned instead. also, important caveat, real talk: MPI does not guarantee that an MPI program can continue past an error — but MPI implementations will attempt to continue whenever possible. so like, she'll try. 🫶

here's the error lineup:

• MPI_SUCCESS — no error at all, the routine completed successfully, we love a clean run 💖
• MPI_T_ERR_INVALID — invalid use of the interface, or bad parameter value(s). check your inputs bestie. 🍓
• MPI_T_ERR_INVALID_HANDLE — the handle is invalid. that wristband did not scan. 💀
• MPI_T_ERR_NOT_INITIALIZED — the MPI tool information interface is not initialized. you gotta turn it on first!! 🙈
• MPI_ERR_OTHER — some other error; use MPI_Error_string to get more information about this error code. she'll tell you what's up. 🔍

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👑 A LIL SIGN-OFF 👑

this page came straight out of the MPI manual, dated 4/10/2026, filed under MPI_T_event_read(3). read her, love her, pass her to your bestie, periodt. 💅💖✨

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