MPI_T_event_set_dropped_handler(3)

💖 MPI_T_event_set_dropped_handler(3) 💖

okay bestie, we're deep in the MPI manual pages right now (yes, that MPI) and this one is genuinely a little gem. it's MPI_T_event_set_dropped_handler, and no cap, the name is literally a whole sentence. buckle up 🎀

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✨ NAME ✨

MPI_T_event_set_dropped_handler — registers a function to be called when event information is dropped for the registration handle specified in event_registration 🫶

like... you're telling MPI "hey, if you ever gotta ghost some event info, pls call this function of mine so i at least know it happened." very considerate of you, honestly.

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🌸 SYNOPSIS 🌸

int MPI_T_event_set_dropped_handler(MPI_T_event_registration event_registration,
MPI_T_event_dropped_cb_function dropped_cb_function)

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🦋 INPUT PARAMETERS 🦋

• event_registration — a valid event registration (it's a handle, babes). it has to be valid, or... well, peep the ERRORS section 💅
• dropped_cb_function — pointer to a user-defined callback function (it's a function). your function. you wrote it. iconic.

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🧚 THREAD AND INTERRUPT SAFETY 🧚

okay so this routine is thread-safe 👑 meaning you can safely call it from multiple threads at the same time and you do not need to bring your own user-provided thread locks. no extra mutexes, no babysitting. slay.

but — and this is the important part — the routine 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, the routine's fine in threads but don't go interrupting it, okay? it's giving "do not perceive me while i'm allocating." 💀

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🔥 ERRORS 🔥

so, all MPI routines (except MPI_Wtime and MPI_Wtick — they're the special little exceptions, they don't play by these rules) return an error value. C routines hand it back as the value of the function, and Fortran routines stick 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. yes, fr fr, it just ends everything. 💀

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

and the MPI-1 routine MPI_Errhandler_set may be used too, but its use is deprecated 🙈 (translation: it's giving legacy, don't start anything new with it).

you can also use the predefined error handler MPI_ERRORS_RETURN to make error values actually get returned to you instead of the job just dying.

note that MPI does not guarantee an MPI program can continue past an error. however, MPI implementations will attempt to continue whenever possible. so like... maybe it survives, maybe it doesn't. roll the dice bestie 🎲

here are the specific error values:

• MPI_SUCCESS — no error; the MPI routine completed successfully. we love a happy ending 💖
• MPI_T_ERR_INVALID_HANDLE — the handle is invalid. (told you it had to be valid 👀)
• MPI_T_ERR_NOT_INITIALIZED — the MPI tool information interface is not initialized. you gotta init first, bestie, that's the whole vibe check.
• MPI_ERR_OTHER — other error; use MPI_Error_string to get more information about this error code. it's the "idk, ask MPI_Error_string" error 🌈

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and that's the whole page, no notes ✨ this was MPI manual page MPI_T_event_set_dropped_handler(3), dated 4/10/2026 — go forth and handle your dropped events, main character 🎀💅