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POQuestion about parallel loop in MPI
 

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  1. POQuestion about parallel loop in MPI
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    <p>hey there, I have a short question about openmpi in fortran: i have a code like this:</p> <pre><code>I) definitions of vars &amp; linear code, setting up some vars for later usage II) a while loop which works like that in pseudocode: nr=1 while(true) { filename='result'//nr//'.bin' (nr converted to string) if(!file_exists(filename)) goto 100 // file exists... so do something with it // calculations, read/write... nr=nr+1 } 100 continue III) some more linear code... </code></pre> <p>Now I want to make this a parallel computation with openmpi. The linear code from I) and III) should only be computed once and the while-loops should be run on several processors... How to best realize it? my problem is how the while-loop works: E.g. when processor 1 computes result1.bin, how to directly tell processor 2 to compute result2.bin? and how would it work if there are 30 files and I use </p> <p>mpirun -n 10 my_program</p> <p>? how does MPI "know" that after finishing computing one file, there are more files "waiting" to be processed: as soon as one processor has ended processing one file, THIS procesor should directly start over processing the next file in the queue..</p> <p>thanks so far!</p> # <p>EDIT:</p> # <p>Hey there, it's me again... I wanted to give OpenMP a try too, so I used a chunk of your code which reads the existing files and afterwards loops them (and processes them):</p> <pre><code>nfiles = 0 do write(filename,FMT='(A,I0,A)'), prefix, nfiles+1, suffix inquire(file=trim(filename),exist=exists) if (not(exists)) exit nfiles = nfiles + 1 enddo </code></pre> <p>now I tried the following code:</p> <pre><code>call omp_set_num_threads(2) !$OMP PARALLEL !$OMP DO do i=startnum, endnum write(filename,FMT='(A,I0,A)'), prefix, i, suffix ...CODE DIRECTLY HERE TO PROCESS THE FILE... enddo !$OMP END DO !$OMP END PARALLEL </code></pre> <p>But it gives me always errors like that: "It is illegal to branch out of a DO loop associated with an Open MP DO or PARALLEL DO directive."</p> <p>Always about the codelines with this sort of code:</p> <pre><code>read (F_RESULT,*,ERR=1) variable </code></pre> <p>Where F_RESULT is a filehandle...What could be wrong about it? variable is defined outside of the loop block, and I already tried to set OpenMP directive to </p> <pre><code>private(variable) </code></pre> <p>so that each thread has his own copy, but that didn't work out! Thanks so far for your help!</p>
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    1. USJonathan Dursi
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    1. COEdited to replace openmpi with mpi; this isn't openmpi specific.
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      1. POQuestion about parallel loop in MPI
      1. USJonathan Dursi
 

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