MPI_FILE_READ_ALL(3)

💅 MPI_FILE_READ_ALL(3) — the Open MPI glow-up 🦋

okay so bestie, welcome to the Open MPI manual, section 3 — this is the MPI_File_read_all page and honestly it's giving "collective file reading, but make it blocking" ✨ grab ur iced coffee and let's get into it 💖

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🌸 NAME 🌸

MPI_File_read_all — reads a file starting at the locations specified by individual file pointers (blocking, collective). no cap, that's the whole vibe 💅

✨ SYNTAX ✨

🎀 C Syntax

#include <mpi.h>

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

🎀 Fortran Syntax

USE MPI
! or the older form: INCLUDE 'mpif.h'
MPI_FILE_READ_ALL(FH, BUF, COUNT,
     DATATYPE, STATUS, IERROR)
     <type>  BUF(*)
     INTEGER FH, COUNT, DATATYPE, STATUS(MPI_STATUS_SIZE),IERROR

🎀 Fortran 2008 Syntax

USE mpi_f08
MPI_File_read_all(fh, buf, count, datatype, status, ierror)
     TYPE(MPI_File), INTENT(IN) :: fh
     TYPE(*), DIMENSION(..) :: buf
     INTEGER, INTENT(IN) :: count
     TYPE(MPI_Datatype), INTENT(IN) :: datatype
     TYPE(MPI_Status) :: status
     INTEGER, OPTIONAL, INTENT(OUT) :: ierror

🫶 INPUT PARAMETERS 🫶

these are the things u hand over, bestie 👇

• fh — the file handle (handle). it's literally the lil passport to ur file 🛂
• count — number of elements in buffer (integer). yes, element count, not vibes count 😌
• datatype — data type of each buffer element (handle). this is what tells MPI how to interpret the buffer, slay 🎀

💜 OUTPUT PARAMETERS 💜

what u get back, and it's lowkey the good stuff 🌈

• buf — initial address of buffer (choice). ur data goes here, main character energy only 💅
• status — status object (status). the receipts 📋
• ierror — Fortran only: error status (integer). C girlies, u get the return value instead 😘

🔥 DESCRIPTION 🔥

okay so here's the tea ☕ MPI_File_read_all is a collective routine. what it does: it attempts to read from the file associated with fh — at the current individual file pointer position maintained by the system — a total number of count data items having datatype type into the user's buffer buf. the way that whole sentence works is it's one big read, one big vibe 🦋

the data is taken out of those parts of the file specified by the current view. mmhmm, the view matters, iykyk 👑

MPI_File_read_all stores the number of data-type elements actually read in status. and all other fields of status are undefined — like, undefined undefined, don't go reading them and expecting answers 🙈

💀 warning, bestie: it is erroneous to call this function if MPI_MODE_SEQUENTIAL mode was specified when the file was opened. like, just don't. that's the rule 😭

😭 ERRORS 😭

almost all MPI routines return an error value — C routines as the return result of the function, and Fortran routines in the last argument. periodt 💅

before the error value is returned, the current MPI error handler associated with the communication object (e.g., communicator, window, file) is called. if no communication object is associated with the MPI call, then the call is considered attached to MPI_COMM_SELF and will call the associated MPI error handler. when MPI_COMM_SELF is not initialized (i.e., before MPI_Init/MPI_Init_thread, after MPI_Finalize, or when using the Sessions Model exclusively) the error raises the initial error handler. the initial error handler can be changed by calling MPI_Comm_set_errhandler on MPI_COMM_SELF when using the World model, or the mpi_initial_errhandler CLI argument to mpiexec or info key to MPI_Comm_spawn/MPI_Comm_spawn_multiple. if no other appropriate error handler has been set, then the MPI_ERRORS_RETURN error handler is called for MPI I/O functions and the MPI_ERRORS_ABORT error handler is called for all other MPI functions. ngl that's a whole lot but it's all important 📚

Open MPI includes three predefined error handlers that can be used — iconic lineup honestly 👑

• MPI_ERRORS_ARE_FATAL — causes the program to abort all connected MPI processes. yeah. everyone. 💀
• MPI_ERRORS_ABORT — an error handler that can be invoked on a communicator, window, file, or session. when called on a communicator, it acts as if MPI_Abort was called on that communicator. if called on a window or file, acts as if MPI_Abort was called on a communicator containing the group of processes in the corresponding window or file. if called on a session, aborts only the local process. context is everything, bestie 🎀
• MPI_ERRORS_RETURN — returns an error code to the application. the chill one 🫶

MPI applications can also implement their own error handlers by calling:

• MPI_Comm_create_errhandler then MPI_Comm_set_errhandler
• MPI_File_create_errhandler then MPI_File_set_errhandler
• MPI_Session_create_errhandler then MPI_Session_set_errhandler or at MPI_Session_init
• MPI_Win_create_errhandler then MPI_Win_set_errhandler

note that MPI does not guarantee that an MPI program can continue past an error. so like... plan accordingly 🌸

see the MPI man page for a full list of MPI error codes.

see the Error Handling section of the MPI-3.1 standard for more information. iykyk 📖

👑 COPYRIGHT 👑

2003-2026, The Open MPI Community 🫶

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alright bestie that's the whole page, u ate that 💅✨ and for the sign-off: this beauty is from Open MPI, dated Sep 11, 2026, and it's literally the MPI_FILE_READ_ALL(3) page — go forth and read collectively, queen 👑🌈💖