# Coarray Reading file **URL:** \ **Category:** Help\ **Created:** [August 27, 2023, 7:06am UTC](https://fortran-lang.discourse.group/t/coarray-reading-file/6403 "2023-08-27T07:06:45Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![apoorv01](https://avatars.discourse-cdn.com/v4/letter/a/8e7dd6/32.png) [@apoorv01](https://fortran-lang.discourse.group/u/apoorv01)\ **Post date:** [August 27, 2023, 7:06am UTC](https://fortran-lang.discourse.group/t/coarray-reading-file/6403/1 "2023-08-27T07:06:45Z")
Hi, I am trying to read a file in coarray program (opencoarrays), I am using the condition that it be read when image==1. But it seems that CAFRUN automatically runs all the images available. Is there any way that coarray reads only from the image 1 and do rest of the calculations, by not repeating it for other images. Any advice, help and documentation would be helpful Attached is the source code and dummy file, I am testing. Can we use coarray to read and write in serial mode and do all the numerical operation in parallel mode (something similar to openmp) Thanks and Regards Apurva [Fourth.f90](https://fortran-lang.discourse.group/uploads/short-url/pOqpxPEHXTh7VQQpEEMzuwfqQN7.f90) (568 Bytes) [xy.txt](https://fortran-lang.discourse.group/uploads/short-url/ysbshRpJxabAOi2nNkA2I7du0Aw.txt) (4 Bytes) ---
**Author:** ![Beliavsky](https://avatars.discourse-cdn.com/v4/letter/b/ba8739/32.png) [@Beliavsky](https://fortran-lang.discourse.group/u/Beliavsky)\ **Post date:** [August 27, 2023, 10:52am UTC](https://fortran-lang.discourse.group/t/coarray-reading-file/6403/2 "2023-08-27T10:52:26Z")
For small files it’s easier for people to read and respond if they are pasted in the message. Below are `fourth.f90` and `xy.txt`. ```auto program t1 use, intrinsic :: iso_fortran_env implicit none integer :: n[*],pro,q,me !n=0 !write(*,*)"Called Main Program" me = this_image() pro = num_images() write(*,*)"image : ",this_image() if ( me == 1) then open(unit=input_unit,file="xy.txt",action="read") read(input_unit,*)n do q = 2,pro n[q]=n[1] end do end if write(*,*)"n :",n sync all end program t1 ``` ` 10` ---
**Author:** ![mEm](https://avatars.discourse-cdn.com/v4/letter/m/90ced4/32.png) [@mEm](https://fortran-lang.discourse.group/u/mEm)\ **Post date:** [August 27, 2023, 1:41pm UTC](https://fortran-lang.discourse.group/t/coarray-reading-file/6403/3 "2023-08-27T13:41:29Z")
Hi @apoorv01 , > [@apoorv01](#): > > But it seems that CAFRUN automatically runs all the images available. Is there any way that coarray reads only from the image 1 and do rest of the calculations, by not repeating it for other images. It’s a bit unclear what you mean with these statements. Maybe, a clarification would further help readers understanding your problem and possibly provide ad-hoc solutions for them. In the meantime, I tried your code, and by anticipating that I might have not caught what you actually want to achieve with it, I think there are some tiny logic flaws, specially with the loop ```auto do q = 2,pro n[q]=n[1] end do ``` [Here](https://coarrays.sourceforge.io/doc.html) and [here](https://fortranwiki.org/fortran/show/Coarrays) some references where you can read more about coarrays and how they work in practice. For sure, other more experianced members here can guide you towards more insightful places. In the meantime, I give you a modified version of your code based on what I thought you are trying to attempt: ```auto program test use, intrinsic :: iso_fortran_env implicit none integer :: n[*], nimgs, i_, me, iu = 100 me = this_image() nimgs = num_images() write(*, *) ' Hello from image : ', me, ' of ', nimgs sync all ! Read file only from image 1 if (me == 1) then write(*, *) ' Image ', me, ' reading file...' open(unit=iu, file='xy.txt', form='formatted', action = 'read') read(iu, *) n[1] !<--- NOTE: equivalent "read(iu, *) n" close(iu) write(*, *) ' Image ', me, ' reading file... ok.' endif sync all !<-- in the meantime, the others wait for image 1 to finish its work. n[me] = n[1] + me !<-- Broadcast read value to all other images (1-myself included) ! print results do i_ = 1, nimgs if (me == i_) write(*, *) ' Image ', me, ' : n[me] = ', n[me] sync all enddo end program ``` Hope this helps. Regards. ---
**Author:** ![apoorv01](https://avatars.discourse-cdn.com/v4/letter/a/8e7dd6/32.png) [@apoorv01](https://fortran-lang.discourse.group/u/apoorv01)\ **Post date:** [August 27, 2023, 3:28pm UTC](https://fortran-lang.discourse.group/t/coarray-reading-file/6403/4 "2023-08-27T15:28:48Z")
@mEm, Thank you for your suggestions. This has made me more clear about the input file handling. Let me try the real file I want to read and store data for my program. Best Regards Apurva ---
**Author:** ![FortranFan](https://avatars.discourse-cdn.com/v4/letter/f/96bed5/32.png) [@FortranFan](https://fortran-lang.discourse.group/u/FortranFan)\ **Post date:** [August 27, 2023, 4:53pm UTC](https://fortran-lang.discourse.group/t/coarray-reading-file/6403/5 "2023-08-27T16:53:03Z")
> [@apoorv01](#): > > … Can we use coarray to read and write in serial mode and do all the numerical operation in parallel mode … 1. Refer also to Modern Fortran Explained introducing Fortran 2018 for current facilities including with coarray `TEAMS` 2. Also, evaluate standard facilities with more than one Fortran processor to cross-check standard semantics and to be ultra mindful of compiler deficiences, 3. With a Fortran 2018 and newer Fortran processors, consider coarray intrinsics such as `CO_BROADCAST` for many common tasks. This can be helpful because an author can **allow the processor to do the synchronization** , as necessary. ```fortran integer :: n[*], i ! Simulate file READ if ( this_image() == 1 ) n = 42 call co_broadcast( n, 1 ) ! check values if ( this_image() == 1 ) then print "(g0,t10,g0)", "Image", "n" do i = 1, num_images() print "(g0,t10,g0)", i, n[i] end do end if end ``` ```auto C:\temp>ifort /free /standard-semantics /Qcoarray=shared /Qcoarray-num-images=8 p.f Intel(R) Fortran Intel(R) 64 Compiler Classic for applications running on Intel(R) 64, Version 2021.10.0 Build 20230609_000000 Copyright (C) 1985-2023 Intel Corporation. All rights reserved. Microsoft (R) Incremental Linker Version 14.36.32537.0 Copyright (C) Microsoft Corporation. All rights reserved. -out:p.exe -subsystem:console p.obj C:\temp>p.exe Image n 1 42 2 42 3 42 4 42 5 42 6 42 7 42 8 42 ``` ```auto ``` ---
**Author:** ![Audun](https://avatars.discourse-cdn.com/v4/letter/a/ecd19e/32.png) [@Audun](https://fortran-lang.discourse.group/u/Audun)\ **Post date:** [September 9, 2023, 7:44am UTC](https://fortran-lang.discourse.group/t/coarray-reading-file/6403/6 "2023-09-09T07:44:42Z")
To read a multi record file into a coarray variable with allocatable components you would have to allocate the coarray variable separately on all images, before you can use co\_broadcast? ---
**Author:** ![apoorv01](https://avatars.discourse-cdn.com/v4/letter/a/8e7dd6/32.png) [@apoorv01](https://fortran-lang.discourse.group/u/apoorv01)\ **Post date:** [September 9, 2023, 10:25am UTC](https://fortran-lang.discourse.group/t/coarray-reading-file/6403/7 "2023-09-09T10:25:11Z")
@FortranFan …, Thank you for the reply. I will refer the book mentioned