MPI_Bcast_init(3)

✨ MPI_Bcast_init(3) — the MPI girlies' guide ✨

okay bestie, gather round, we're doing a persistent broadcast request and honestly? it's giving main character energy. this page lives in the MPI manual (section 3, the library calls, you know the vibe) 💅

---

🌸 NAME 🌸

MPI_Bcast_init — creates a persistent request for broadcast

like, you know how MPI_Bcast is a one-and-done situation? this is the committed relationship version. it makes you a persistent request. obsessed. 🫶

---

🎀 SYNOPSIS 🎀

int MPI_Bcast_init(void *buffer, int count, MPI_Datatype datatype, int root,
MPI_Comm comm, MPI_Info info, MPI_Request *request)

int MPI_Bcast_init_c(void *buffer, MPI_Count count, MPI_Datatype datatype,
int root, MPI_Comm comm, MPI_Info info,
MPI_Request *request)

two flavours, no cap — pick the one that matches your count type and slay 💖

---

🦋 INPUT PARAMETERS 🦋

• count — number of entries in buffer. must be a non-negative integer, so like, zero or up. no negatives, we don't do that here.
• datatype — data type of buffer (a handle).
• root — rank of broadcast root (an integer). the one everyone's listening to, the it-girl of the call 👑
• comm — communicator (handle).
• info — info argument (handle).

---

🌈 INPUT/OUTPUT PARAMETERS 🌈

• buffer — starting address of buffer (choice).

yes it's in the in/out section, yes that's on purpose, the broadcast reads from it at the root and writes into it everywhere else, iykyk 💜

---

⭐ OUTPUT PARAMETERS ⭐

• request — communication request (handle). your shiny new persistent request, take care of it 🎀

---

💅 THREAD AND INTERRUPT SAFETY 💅

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. we love a low-maintenance icon.

however — and this is the important part — the routine is not interrupt safe. typically this is due to the use of memory allocation routines such as malloc or other non-MPICH runtime routines that are themselves not interrupt-safe. so like, mind the signals, okay? 🙈

---

🧚 NOTES FOR FORTRAN 🧚

• All MPI routines in Fortran (except for MPI_WTIME and MPI_WTICK) have an additional argument ierr at the end of the argument list. ierr is an integer and has the same meaning as the return value of the routine in C.
• In Fortran, MPI routines are subroutines, and are invoked with the call statement.
• All MPI objects (e.g., MPI_Datatype, MPI_Comm) are of type INTEGER in Fortran.

fr fr, Fortran besties get an extra lil argument and everything's just INTEGER. iconic behaviour. ✨

---

🔥 ERRORS 🔥

okay so this is the part where we get real. All MPI routines (except MPI_Wtime and MPI_Wtick) return an error value; C routines as the value of the function and Fortran routines in the last argument. Before the value is returned, the current MPI error handler is called.

⚠️ By default, this error handler aborts the MPI job. like, the whole thing. gone. dramatic but true 😭

The error handler may be changed 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 its use is deprecated (bestie... don't).

The predefined error handler MPI_ERRORS_RETURN may be used to cause error values to be returned. Note that MPI does not guarantee that an MPI program can continue past an error; however, MPI implementations will attempt to continue whenever possible.

here's the error roster, no skipping:

• MPI_SUCCESS — No error; MPI routine completed successfully. the dream. green flags only 🌸
• MPI_ERR_ARG — Invalid argument. Some argument is invalid and is not identified by a specific error class (e.g., MPI_ERR_RANK).
• MPI_ERR_BUFFER — Invalid buffer pointer. Usually a null buffer where one is not valid.
• MPI_ERR_COMM — Invalid communicator. A common error is to use a null communicator in a call (not even allowed in MPI_Comm_rank).
• MPI_ERR_COUNT — Invalid count argument. Count arguments must be non-negative; a count of zero is often valid.
• MPI_ERR_INFO — Invalid Info.
• MPI_ERR_TYPE — Invalid datatype argument. Additionally, this error can occur if an uncommitted MPI_Datatype (see MPI_Type_commit) is used in a communication call.
• MPI_ERR_OTHER — Other error; use MPI_Error_string to get more information about this error code.

---

and that's the whole page, bestie, you ate that 🍓 this cutie is from the MPI manual, MPI_Bcast_init(3), dated 4/10/2026 — go forth and broadcast persistently, mwah 💖✨👑