Running Shell Script having multiple programs dynamically in parallel - bash

Question

I have a shell script which captures the Process ID, CPU and Memory of the JVM every nth second and writes the output to a file. Below is my code:
JVM="aaa001_bcdefx01"
systime=$(date +"%m-%d-%y-%T")
for i in {1..10}
do
PID=`ps -auxwww | grep "jdk" | grep $JVM | grep -v grep | cut -c -30 | awk '{print $2}'`
MEM=`ps -auxwww | grep "jdk" | grep $JVM | grep -v grep | cut -c -30 | awk '{print $4 }'`
CPU=`ps -auxwww | grep "jdk" | grep $JVM | grep -v grep | cut -c -30 | awk '{print $3 }'`
printf '%-5s %-20s %-20s %-20s %-20s \n' "$systime $JVM $PID $CPU $MEM " >> $LOGFILE
sleep 5
done
This run perfectly fine when i have only one JVM in that server. How can i execute the same script in parallel and fetch the details if i have multiple JVM for a server.
I looked for some solutions and found & to be used in the script but couldn't understand how this can be implemented to my above script. Let's say I have 5 JVMs. How can i run the script and fetch the stats in parallel for all the below JVMs in parallel. Kindly guide. Any help would be appreciated.
JVM="aaa001_bcdefx01"
JVM="aaa002_bcdefx01"
JVM="aaa003_bcdefx01"
JVM="aaa004_bcdefx01"
JVM="aaa005_bcdefx01"

Answer 1

GNU Parallel is made for this kind of stuff
doit() {
JVM="$1"
systime=$(date +"%m-%d-%y-%T")
for i in {1..10}
do
PID=`ps -auxwww | grep "jdk" | grep $JVM | grep -v grep | cut -c -30 | awk '{print $2}'`
MEM=`ps -auxwww | grep "jdk" | grep $JVM | grep -v grep | cut -c -30 | awk '{print $4 }'`
CPU=`ps -auxwww | grep "jdk" | grep $JVM | grep -v grep | cut -c -30 | awk '{print $3 }'`
printf '%-5s %-20s %-20s %-20s %-20s \n' "$systime $JVM $PID $CPU $MEM "
sleep 5
done
}
export -f doit
parallel -j0 --linebuffer --tag doit ::: aaa00{1..5}_bcdefx01 >> $LOGFILE
The function is basically your code. The change is that it takes the JVM as argument and it prints to stdout (standard output). GNU Parallel calls the function with the arguments aaa00N_bcdefx01 where N = 1..5, and saves the output to $LOGFILE. It uses --linebuffer to pass the output as soon as there is a full line, and thus guarantees that you will not get half-a-line from one process mixed with a line from another process. --tag prepends the line with the JVM.

Answer 2

How about using subshell?
Each JVM shell script should go inside '(' and ')'. Put '&' at the end so that it executes in the background.
An example is given here.
#!/bin/bash
echo > testfile.txt
echo "execute subshell 1"
(
#JVM 1 should go here
sleep 10
echo "subshell 1" >> testfile
)&
echo "execute subshell 2"
(
#JVM 2 should go here
sleep 10
echo "subshell 2" >> testfile
)&
echo "execute subshell 3"
(
#JVM 3 should go here
sleep 10
echo "subhsell 3" >> testfile
)&
Here each subshell writes data to testfile.txt after waiting for 10 seconds.