Batch Process Runner in bash shell

Picked up an interesting problem from a colleague:

How to run n batch processes but only m at a time?

It seems that resource constraints allow every four batch processes to share one license - so long as all four batch processes are started from the same terminal on the same machine. Users may have tens of processes to run and currently they are run individually on our compute farm.



I tend to code whilst having a cold for some reason? And needed to use more advanced bash scripting - I decided against Python for the task as I would like my colleague to take over further developments of the code and I can't rely on him knowing Python, (and I don't want to code in Perl today).



I came up with this little demonstrator which runs processes that go to sleep for a random amount of time. The script runs as many as you specify but only a maximum number of proc's at a time.



The script is followed by sample output and was tested on cygwin using bash version 3.2.9(11)-release (i686-pc-cygwin):

  1 #!/bin/bash
  2 
  3 ##
  4 ## process_runner.sh <concurrent> <total procs>
  5 ##
  6 ## Example script given the maximum number of processes to
  7 ## run concurrently, c, and the total number of processes, n
  8 ## runs at most c, processes in the background until all n
  9 ## Have been run.
 10 ##
 11 ## Author Donald 'Paddy' McCarthy Dec. 17 2007
 12 ##
 13 
 14 # how many processes to run in parallel
 15 concurrent=$1
 16 # total processes to run
 17 maxprocs=$2
 18 
 19 printf "\n## STARTING %i Processes, %i at a time\n\n" \
 20   $maxprocs $concurrent
 21 
 22 
 23 # main loop wait time between checking background procs.
 24 tick=1
 25 
 26 
 27 # dummy processes sleep for a random time
 28 function runproc {
 29   local -i n=$1
 30   local -i j
 31   (( j = 5+$RANDOM*10/32767 ))
 32   #(date; printf "#>>>JOB %i : Sleeping for %i\n" $n $j)
 33   printf "OUT JOB ,%03i, Sleep for ,%2i,  , @,%s\n" $n $j "`date`"
 34   sleep $j
 35   returned=$?
 36   printf "IN  JOB ,%03i, Slept for ,%2i, returned ,%i, @,%s\n" \
 37     $n $j $returned "`date`"
 38   #(date; printf "#<<<JOB %i : Slept for %i\n" $n $j)
 39 }
 40 
 41 function print_runstats {
 42   printf '# %i Jobs in background. %i/%i started\n\n'  \
 43     `jobs -r|wc -l` $ran $maxprocs
 44 }
 45 
 46 # Bash array running keeps track of the background process numbers
 47 # Start with nothing running (sentinel value will not be a process number
 48 for ((i=0; i<$concurrent; i+=1 )); do running[$i]=123456789; done
 49 
 50 ran=0
 51 until
 52   while [ $ran -lt $maxprocs ]; do
 53     for ((p=0; p<$concurrent; p+=1 )); do
 54       proc=${running[$p]}
 55       # Over all running processes...
 56       # $proc still running?
 57       ps -p $proc | fgrep $proc >/dev/null
 58       if [ $? -ne '0' ] ; then
 59         # Not found  i.e. finished
 60         # Run another in background and store the proc number
 61         runproc $ran &
 62         running[$p]=$!
 63         ((ran+=1))
 64         if [ $ran -ge $maxprocs ]; then break 1; fi
 65       fi
 66     done
 67     sleep $tick
 68     # Status
 69     print_runstats
 70   done
 71 
 72   sleep $tick
 73   # Status
 74   print_runstats
 75 do [  `jobs -r|wc -l` -eq 0 ]
 76 done
 77 wait
 78 printf "\n## FINISHED\n"
 79 
 80 exit 0
 81 
 82 sample_output=<<!
 83 bash$ ./process_runner.sh 2 5
 84 
 85 ## STARTING 5 Processes, 2 at a time
 86 
 87 OUT JOB ,000, Sleep for ,10,  , @,Tue Dec 18 09:26:00 GMTST 2007
 88 OUT JOB ,001, Sleep for , 8,  , @,Tue Dec 18 09:26:00 GMTST 2007
 89 # 2 Jobs in background. 2/5 started
 90 
 91 # 2 Jobs in background. 2/5 started
 92 
 93 # 2 Jobs in background. 2/5 started
 94 
 95 # 2 Jobs in background. 2/5 started
 96 
 97 # 2 Jobs in background. 2/5 started
 98 
 99 # 2 Jobs in background. 2/5 started
100 
101 IN  JOB ,001, Slept for , 8, returned ,0, @,Tue Dec 18 09:26:09 GMTST 2007
102 # 1 Jobs in background. 2/5 started
103 
104 OUT JOB ,002, Sleep for ,11,  , @,Tue Dec 18 09:26:09 GMTST 2007
105 IN  JOB ,000, Slept for ,10, returned ,0, @,Tue Dec 18 09:26:10 GMTST 2007
106 # 2 Jobs in background. 3/5 started
107 
108 OUT JOB ,003, Sleep for , 7,  , @,Tue Dec 18 09:26:11 GMTST 2007
109 # 2 Jobs in background. 4/5 started
110 
111 # 2 Jobs in background. 4/5 started
112 
113 # 2 Jobs in background. 4/5 started
114 
115 # 2 Jobs in background. 4/5 started
116 
117 # 2 Jobs in background. 4/5 started
118 
119 IN  JOB ,003, Slept for , 7, returned ,0, @,Tue Dec 18 09:26:18 GMTST 2007
120 # 1 Jobs in background. 4/5 started
121 
122 OUT JOB ,004, Sleep for , 6,  , @,Tue Dec 18 09:26:19 GMTST 2007
123 # 2 Jobs in background. 5/5 started
124 
125 IN  JOB ,002, Slept for ,11, returned ,0, @,Tue Dec 18 09:26:20 GMTST 2007
126 # 1 Jobs in background. 5/5 started
127 
128 IN  JOB ,004, Slept for , 6, returned ,0, @,Tue Dec 18 09:26:25 GMTST 2007
129 
130 ## FINISHED
131 !
132 
133 
134 
135 
136