Bash: Running the same program over multiple cores

Question

I have access to a machine where I have access to 10 of the cores -- and I would like to actually use them. What I am used to doing on my own machine would be something like this:

for f in *.fa; do
  myProgram (options) "./$f" "./$f.tmp"
done

I have 10 files I'd like to do this on -- let's call them blah00.fa, blah01.fa, ... blah09.fa.

The problem with this approach is that myProgram only uses 1 core at a time, and doing it like this on the multi-core machine I'd be using 1 core at a time 10 times, so I wouldn't be using my mahcine to its max capability.

How could I change my script so that it runs all 10 of my .fa files at the same time? I looked at Run a looped process in bash across multiple cores but I couldn't get the command from that to do what I wanted exactly.

Answer 1

You could use

for f in *.fa; do
    myProgram (options) "./$f" "./$f.tmp" &
done
wait

which would start all of you jobs in parallel, then wait until they all complete before moving on. In the case where you have more jobs than cores, you would start all of them and let your OS scheduler worry about swapping processes in an out.

One modification is to start 10 jobs at a time

count=0
for f in *.fa; do
    myProgram (options) "./$f" "./$f.tmp" &
    (( count ++ ))        
    if (( count = 10 )); then
        wait
        count=0
    fi
done

but this is inferior to using parallel because you can't start new jobs as old ones finish, and you also can't detect if an older job finished before you manage to start 10 jobs. wait allows you to wait on a single particular process or all background processes, but doesn't let you know when any one of an arbitrary set of background processes complete.

Answer 2

# Wait while instance count less than $3, run additional instance and exit
function runParallel () {
    cmd=$1
    args=$2
    number=$3
    currNumber="1024"
    while true ; do
        currNumber=`ps -e | grep -v "grep" | grep " $1$" | wc -l`
        if [ $currNumber -lt $number ] ; then
            break
        fi
        sleep 1
    done
    echo "run: $cmd $args"
    $cmd $args &
}

loop=0
# We will run 12 sleep commands for 10 seconds each 
# and only five of them will work simultaneously
while [ $loop -ne 12 ] ; do
    runParallel "sleep" 10 5
    loop=`expr $loop + 1`
done

Answer 3

Have you considered using Parallel ?

Answer 4

With GNU Parallel you can do:

parallel myProgram (options) {} {.}.tmp ::: *.fa

From: http://git.savannah.gnu.org/cgit/parallel.git/tree/README

= Full installation =

Full installation of GNU Parallel is as simple as:

./configure && make && make install

If you are not root you can add ~/bin to your path and install in ~/bin and ~/share:

./configure --prefix=$HOME && make && make install

Or if your system lacks 'make' you can simply copy src/parallel src/sem src/niceload src/sql to a dir in your path.

= Minimal installation =

If you just need parallel and do not have 'make' installed (maybe the system is old or Microsoft Windows):

wget http://git.savannah.gnu.org/cgit/parallel.git/plain/src/parallel
chmod 755 parallel
cp parallel sem
mv parallel sem dir-in-your-$PATH/bin/

Watch the intro videos to learn more: https://www.youtube.com/playlist?list=PL284C9FF2488BC6D1