MPI_File_read_all(3)

💖 MPI_File_read_all(3) — the MPI bestie guide 💖

okay so you're in the MPI section 3 girlies now, welcome, this is MPI_File_read_all and she is a whole vibe.

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✨ NAME ✨

MPI_File_read_all — collective read using individual file pointer 🫶

like. everyone reads. together. but each one of you is reading from your own file pointer. it's giving group project but everyone's actually doing their part.

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🌸 SYNOPSIS 🌸

int MPI_File_read_all(MPI_File fh, void *buf, int count, MPI_Datatype datatype,
MPI_Status *status)

int MPI_File_read_all_c(MPI_File fh, void *buf, MPI_Count count,
MPI_Datatype datatype, MPI_Status *status)

two flavors, bestie: the classic one with an int count, and the _c one that takes an MPI_Count count for when your counts are lowkey huge. slay.

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💅 INPUT PARAMETERS 💅

• fh — file handle (handle). the lil ID card for the file you're reading from 🎀
• count — number of elements in buffer (integer). how many of the things you want ✨
• datatype — datatype of each buffer element (handle). what kind of thing each element is 👑

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🦋 OUTPUT PARAMETERS 🦋

• buf — initial address of buffer (choice). where the good stuff lands 💖
• status — status object (Status). the receipts 📋

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🔥 THREAD AND INTERRUPT SAFETY 🔥

this routine is thread-safe. translation: multiple threads can use it at the same time and you do not need to bring your own thread locks. no cap, she handles herself. main character energy.

however — and this is the plot twist — the routine is not interrupt safe. 😭 typically this is because it uses memory allocation routines like malloc or other non-MPICH runtime routines, and those are themselves not interrupt-safe. so like, not her fault, but still. be aware.

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🌈 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. periodt.

In Fortran, MPI routines are subroutines, and they are invoked with the call statement.

All MPI objects (e.g., MPI_Datatype, MPI_Comm) are of type INTEGER in Fortran. that's just the rules fr fr 💜

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💀 ERRORS 💀

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. yes, literally, it will just end everything 💀

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 🙈. 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. they're trying their best, ok?

• MPI_SUCCESS — No error; MPI routine completed successfully. we love to see it 🎉
• 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. bestie the buffer is null 😭
• MPI_ERR_COUNT — Invalid count argument. Count arguments must be non-negative; a count of zero is often valid.
• 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 before you use them, that's the rule 💅
• MPI_ERR_OTHER — Other error; use MPI_Error_string to get more information about this error code. the mystery box of errors 📦

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okay that's the whole page, you ate that. go read your files collectively, icon 👑

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this was the MPI_File_read_all(3) page from the MPI manual, dated 4/10/2026. mwah 💋 bye bestie 🦋✨