MPI_File_write_all_begin(3)

💖 MPI_File_write_all_begin(3) 💖

okay bestie, welcome to the MPI manual, the one and only 🌈 — we're talking MPI_File_write_all_begin today and honestly? it's giving setup era.

---

✨ NAME ✨

MPI_File_write_all_begin — Begin a split collective write using

(yes the sentence just ends there, no cap, it's giving cliffhanger energy 💅)

---

🦋 SYNOPSIS 🦋

int MPI_File_write_all_begin(MPI_File fh, const void *buf, int count,
MPI_Datatype datatype)

int MPI_File_write_all_begin_c(MPI_File fh, const void *buf, MPI_Count count,
MPI_Datatype datatype)

like look at her, two whole forms, one for the regular girlies and one _c for the big-count girlies 👑

---

🌸 INPUT PARAMETERS 🌸

• fh — the file handle, your little ticket to the file in question 🎟️ (handle)
• buf — initial address of the buffer, like where the vibes start ✨ (choice)
• count — number of elements in the buffer, so how many lil guys we're working with (integer)
• datatype — datatype of each buffer element, aka what each element is (handle)

---

🧚 THREAD AND INTERRUPT SAFETY 🧚

thread-safe!! yes queen 💖 that means multiple threads can use this routine at the same time, safely, and you do not need to bring your own thread locks. no gatekeeping, no extra work, we love to see it.

BUT 🚨 she is not interrupt safe, and that's real. usually this is because memory allocation routines like malloc, or other non-MPICH runtime routines, are themselves not interrupt-safe. so like, don't come for her when the interrupt hits, k? 😭

---

💜 NOTES FOR FORTRAN 💜

all MPI routines in Fortran (except for MPI_WTIME and MPI_WTICK) get an extra argument called ierr tacked on at the end of the argument list. ierr is an integer and it means the exact same thing as the return value of the routine in C. and in Fortran, MPI routines are subroutines, invoked with the call statement — that's just how it is 🫶

also: all MPI objects (like MPI_Datatype, MPI_Comm) are of type INTEGER in Fortran. periodt.

---

💀 ERRORS 💀

okay so here's the deal with error values. all MPI routines (except MPI_Wtime and MPI_Wtick) return an error value — C routines give it as the value of the function, Fortran routines give it in that last argument. and before the value is even returned, the current MPI error handler gets called. by default, that error handler aborts the MPI job, which, yeah, dramatic but true.

you can swap the handler 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 its use is deprecated, so like, read the room 👀. the predefined error handler MPI_ERRORS_RETURN may be used to cause error values to be returned.

also note: MPI does not guarantee that an MPI program can continue past an error. however, MPI implementations will attempt to continue whenever possible. she tries her best 🥺

the codes, bestie:

• MPI_SUCCESS — no error; the MPI routine completed successfully. slay 💅
• MPI_ERR_BUFFER — invalid buffer pointer. usually a null buffer where one is not valid. not her fault 🙈
• MPI_ERR_COUNT — invalid count argument. count arguments must be non-negative; a count of zero is often valid. zero is fine, negative is not, be serious 🌸
• 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. commit your types bestie, it's the bare minimum 🎀
• MPI_ERR_OTHER — other error; use MPI_Error_string to get more information about this error code. the mysterious one, the enigma, the "use MPI_Error_string" one ✨

---

💌 and that's the whole page!! this was version MPI, dated 4/10/2026, and she remains MPI_File_write_all_begin(3) to the very end. mwah, go write something iconic 🫶💖🦋