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I have a question about MPI. I want to have processes read a binary file simultaneously and therefore I'm trying to use MPI_File_iread, but it is not working as I'd expect and I don't know what's wrong.

Sorry if the format of the question is not correct, I am new here.

Here is my code (NINTCI is an integer pointer, file_name is a char array that has the file name already):

#include "mpi.h"

[...]

MPI_Request request;
MPI_Status status;
MPI_File fp;
MPI_File_open(MPI_COMM_WORLD, file_name, MPI_MODE_RDONLY, MPI_INFO_NULL, &fp);

MPI_File_iread(fp, NINTCI, 1, MPI_INT, &request);
MPI_Wait(&request, &status);

printf("%d\n", *NINTCI);
MPI_Barrier(MPI_COMM_WORLD);

The correct number printed should be 0 for all processes, but instead I get random numbers like the following (8 processes):

-1475867408
1495223536
-219489040
-840278800
629550320
1309351152
-321049360
21273840

Funny thing is if I replace the MPI_File_iread with MPI_File_read and remove the MPI_Wait the result is correct.

Does anybody have an idea what I'm doing wrong? Thanks in advance!

Gandharva
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1 Answers1

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You do not check any of your error codes. Does the file exist? Does it have proper permissions? All these answers and more can be yours if you check errors.

See How to use and interpret MPI-IO Error codes? for an example of how to get meaningful information out of your MPI implementation.

Community
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Rob Latham
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