MPI_T_INIT_THREAD(3)

💅 MPI_T_INIT_THREAD(3) — like, the Open MPI one, bestie ✨

okay so this is the Open MPI manual page for MPI_T_init_thread, and honestly? it's giving "small function, big responsibilities." sit down, grab a strawberry drink 🍓, and let's get into it.

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🌸 SYNTAX 🌸

C Syntax

#include <mpi.h>

int MPI_T_init_thread(int required, int *provided)

literally that's it. two args. iconic behavior honestly.

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🫶 INPUT PARAMETERS 🫶

• required — the level of thread support you want (it's an integer). think of it as your wish list, not a promise 💫

🎀 OUTPUT PARAMETERS 🎀

• provided — the level of thread support you actually got (also an integer). yes, they can be different. yes, that's the whole point. iykyk 😭

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✨ DESCRIPTION ✨

so MPI_T_init_thread() initializes the MPI Tool information interface. that's the main character move here.

here's the vibe check on timing, and this part is important bestie: calls to MPI tool functions are allowed at any point in execution — including before MPI_Init() and after MPI_Finalize() — as long as two things hold:

1. MPI_T_init_thread() has been called at least once, and
2. the number of calls to MPI_T_init_thread() is greater than the number of calls to MPI_T_finalize().

and if at any point in execution the number of calls to MPI_T_finalize() equals the number of calls to MPI_T_init_thread()? 💀 the MPI tool interface will no longer be available until another call to MPI_T_init_thread(). it's a whole balance-the-scales situation. no cap.

now, MPI_T_init_thread(), like MPI_Init_thread(), has a provision to request a certain level of thread support in required. the options are:

• MPI_THREAD_SINGLE — only one thread will execute. solo era. 🧚
• MPI_THREAD_FUNNELED — if the process is multithreaded, only the thread that called MPI_Init_thread will make MPI calls.
• MPI_THREAD_SERIALIZED — if the process is multithreaded, only one thread will make MPI library calls at one time. one at a time, we take turns, we're polite 💅
• MPI_THREAD_MULTIPLE — if the process is multithreaded, multiple threads may call MPI at once with no restrictions. chaos mode, but make it legal 🔥

the level of thread support available to the program is set in provided. in Open MPI, that value is dependent on how the library was configured and built. and here's the tea: there is no guarantee that provided will be greater than or equal to required. 🫠

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⭐ NOTES ⭐

it is the caller's responsibility to check the value of provided, because it may be less than what you requested in required. so like… actually look at it. please. i'm begging 🙈

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💀 ERRORS 💀

MPI_T_init_thread will fail if:

• MPI_T_ERR_MEMORY — out of memory 😭
• MPI_T_ERR_CANNOT_INIT — the interface is not in the state to be initialized

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👑 SEE ALSO 👑

• MPI_T
• MPI_Init
• MPI_Init_thread

go read those next, they're all connected, it's a whole ecosystem fr fr 🦋

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🌈 COPYRIGHT 🌈

copyright 2003-2026, The Open MPI Community — all theirs, none of it mine 💖

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and that's the page!! mwah 💋 — this little gem is from the Open MPI crew, dated Sep 11, 2026, and you read the MPI_T_INIT_THREAD(3) page, slay 🎀✨