并行运行多进程的Bash脚本 | A srcipt for running processes in parallel in Bash

原文:http://pebblesinthesand.wordpress.com/2008/05/22/a-srcipt-for-running-processes-in-parallel-in-bash/

技巧是控制了最大并发数目，当前并发数过大时，等待有进程退出才开始下一个。

我现在正在写的脚本里正需要这个，借鉴过来

#!/bin/bash
NUM=0
QUEUE=""
MAX_NPROC=2 # default
REPLACE_CMD=0 # no replacement by default
USAGE="A simple wrapper for running processes in parallel.
Usage: `basename $0` [-h] [-r] [-j nb_jobs] command arg_list
  -h  Shows this help
 -r  Replace asterix * in the command string with argument
 -j nb_jobs  Set number of simultanious jobs [2]
 Examples:
  `basename $0` somecommand arg1 arg2 arg3
  `basename $0` -j 3 \"somecommand -r -p\" arg1 arg2 arg3
  `basename $0` -j 6 -r \"convert -scale 50% * small/small_*\" *.jpg"

function queue {
 QUEUE="$QUEUE $1"

 NUM=$(($NUM+1))
}

function regeneratequeue {
 OLDREQUEUE=$QUEUE
 QUEUE=""
 NUM=0
 for PID in $OLDREQUEUE
 do
  if [ -d /proc/$PID  ] ; then
   QUEUE="$QUEUE $PID"
   NUM=$(($NUM+1))
  fi
 done
}

function checkqueue {
 OLDCHQUEUE=$QUEUE
 for PID in $OLDCHQUEUE
 do
  if [ ! -d /proc/$PID ] ; then
   regeneratequeue # at least one PID has finished
   break
  fi
 done
}

# parse command line
if [ $# -eq 0 ]; then #  must be at least one arg
 echo "$USAGE" >&2
 exit 1
fi

while getopts j:rh OPT; do # "j:" waits for an argument "h" doesnt
    case $OPT in
 h) echo "$USAGE"

  exit 0 ;;
 j) MAX_NPROC=$OPTARG ;;
 r) REPLACE_CMD=1 ;;
 \?) # getopts issues an error message
  echo "$USAGE" >&2
  exit 1 ;;
    esac
done

# Main program
echo Using $MAX_NPROC parallel threads
shift `expr $OPTIND - 1` # shift input args, ignore processed args
COMMAND=$1
shift

for INS in $* # for the rest of the arguments
do
 # DEFINE COMMAND
 if [ $REPLACE_CMD -eq 1 ]; then
  CMD=${COMMAND//"*"/$INS}
 else
  CMD="$COMMAND $INS" #append args
 fi
 echo "Running $CMD" 

 $CMD &
 # DEFINE COMMAND END

 PID=$!
 queue $PID

 while [ $NUM -ge $MAX_NPROC ]; do
  checkqueue
  sleep 0.4
 done
done
wait # wait for all processes to finish before exit

---

Original posted at: http://pebblesinthesand.wordpress.com/2008/05/22/a-srcipt-for-running-processes-in-parallel-in-bash/

This script will run multiple process in background concurrently, while the maximum number of running processed is under control. When there are already too many running processes, a new one will wait until one process finished.

I just need this trick in my project, so I copied it here.

(See codes above)