MPIX_Threadcomm_finish(3)

✨ MPIX_Threadcomm_finish ✨

okay bestie so this one is a page from the MPI manual, section 3, and it's all about MPIX_Threadcomm_finish — the girl whose whole job is finishing (and deactivating 💅) a thread communicator from inside thread parallel regions. yes, inside. she's an indoor cat. 🐈

---

🌸 NAME 🌸

MPIX_Threadcomm_finish — finish/deactiviate a thread communicator (inside thread parallel regions)

(yes it says "deactiviate", that's the original spelling, we respect our elders 💖)

---

🎀 SYNOPSIS 🎀

int MPIX_Threadcomm_finish(MPI_Comm threadcomm)

---

💖 INPUT PARAMETERS 💖

• threadcomm — thread communicator (handle). that's the whole input list. one (1) girl. she's a handle. 🫶

---

🦋 THREAD AND INTERRUPT SAFETY 🦋

k so this routine is thread-safe — which means literally so many threads can call it at once without you having to build your own lil user-provided thread locks. no cap. 🔥

BUT — and this is the important part, look at me — it is not interrupt safe. not even a little. and why? typically because it uses memory allocation routines like malloc or other non-MPICH runtime routines that are themselves not interrupt-safe. so like, yes to threads, no to interrupts. two different vibes entirely. 💀

---

🌈 NOTES FOR FORTRAN 🌈

• every MPI routine in Fortran (except for MPI_WTIME and MPI_WTICK) has an extra argument called ierr chillin' at the very end of the argument list. ierr is an integer and it means exactly the same thing as the return value of the routine in C.
• in Fortran, MPI routines are subroutines, and you invoke them with the call statement. periodt.
• every MPI object (like MPI_Datatype, MPI_Comm) is of type INTEGER in Fortran. every single one. 💜

---

👑 ERRORS 👑

bestie, gather round. every MPI routine (except MPI_Wtime and MPI_Wtick) returns an error value: C routines give it back as the value of the function, and Fortran routines put it in the last argument. but before that value even comes back to you, the current MPI error handler gets called. and by default? that error handler aborts the MPI job. 😭 so yeah. dramatic.

good news: you can change the error handler:

• 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, but its use is deprecated (so like, don't, but you can, iykyk).

the predefined error handler MPI_ERRORS_RETURN may be used to cause error values to be returned instead. ⭐

also important: MPI does not guarantee that an MPI program can continue past an error. however, MPI implementations will attempt to continue whenever possible. so it's giving "we'll try our best" energy, not "we promise". 🙈

now the error codes themselves:

• MPI_SUCCESS — no error; MPI routine completed successfully. she ate. ✨
• MPI_ERR_COMM — invalid communicator. a common error is to use a null communicator in a call (not even allowed in MPI_Comm_rank). literally not allowed. not even there.
• MPI_ERR_OTHER — other error; use MPI_Error_string to get more information about this error code. the catch-all girlie. 💅

---

💜 SEE ALSO 💜

• MPIX_Threadcomm_init
• MPIX_Threadcomm_start
• MPIX_Threadcomm_free

the whole squad fr fr. go read them too, you'll be obsessed. 🧚

---

aaaand that's the page!! 🌸 mwah 💖 this one came from the MPI manual, dated 4/10/2026, and the footer said MPIX_Threadcomm_finish(3) — so when you're done finishing your thread communicator, close the tab and go drink some water bestie. hydration is main character energy. 🍓👑