I am trying to get a concept where I can create simultaneous running child processes from a parent and able to read their exit status as soon as they come in. Once the exit code is read it will start a new child to take its place. That way there is alway 10 children running at once.
In the end I am going to be using this for a way to do asynchronous wgets to speed up my wget scripting. So if you have an alternative, let me know. Thats also why I set a randomized timer on the example child process to simulate wgets and so I can check if it doesnt do things in order or not.
Here is the child process I am threading, just for reference:
Code:
number=0
let "number = $RANDOM % 20"
time=$(echo "1+$number*0.1" | bc)
sleep $time
echo "I got $1 ($time)"
exit $1
I first started out with this job script I found. I realized that it didnt get the exit codes fast enough. I wanted the exit code retrieved as soon as the process is exited.
Code:
#!/bin/bash
MAXJOBS=10
function jobidfromstring()
{
local STRING;
local RET;
STRING=$1;
RET="$(echo $STRING | sed 's/^[^0-9]*//' | sed 's/[^0-9].*$//')"
echo $RET;
}
function clearToSpawn
{
local JOBCOUNT="$(jobs -r | grep -c .)"
if [ $JOBCOUNT -lt $MAXJOBS ] ; then
echo 1;
return 1;
fi
echo 0;
return 0;
}
JOBLIST=""
for (( i=0; i<=20; i++ ));
do
while [ `clearToSpawn` -ne 1 ] ; do
sleep 0.5
done
./child $i &
LASTJOB=`jobidfromstring $(jobs %%)`
JOBLIST="$JOBLIST $LASTJOB"
done
for JOB in $JOBLIST ; do
wait %$JOB
echo "Job $JOB exited with status $?"
done
echo "Done."
Then I decided to tryout the SIGCHLD handler and see how that worked. It turned out that I wasn't able to define the handler in a way that would capture every child for some reason.
Code:
#!/bin/bash
iNext=0
function ChildReturned() {
wait $1
echo "$1 was returned. Its exits status was: $?"
iNext=$((iNext+1))
StartChild $iNext
}
function StartChild {
./child $1 &
pid=$!
echo "Started: $1 PID= $pid"
trap 'ChildReturned $pid' SIGCHLD
}
set -bm
for (( iNext=0; iNext<=10; iNext++ ));
do
StartChild $iNext
done
wait
Finally I tried just starting the children and looping through a while statement that would check when each one died, retrieve the exit code, and then start a new child. However I realized that a child that terminates (SIGCHLD) still exists as a process until you get the exit code with wait(). Therefore using kill -0 wasnt going to work.
Code:
#!/bin/bash
throttle=10
iNext=0
JobIDArray[0]=""
function jobidfromstring()
{
local STRING;
local RET;
STRING=$1;
RET="$(echo $STRING | sed 's/^[^0-9]*//' | sed 's/[^0-9].*$//')"
echo $RET;
}
function AnyAlive {
for (( i=1; i<=throttle; i++ )); do
if kill -0 %${JobIDArray[i]} > /dev/null 2>&1; then
echo 1
return 1
fi
done
echo 0
return 0
}
for (( iNext=1; iNext<=throttle; iNext++ )); do
./child $iNext &
JobIDArray[iNext]=`jobidfromstring $(jobs %%)`
echo " JobIDArray[$iNext] = ${JobIDArray[iNext]}"
done
while [[ `AnyAlive` -eq 1 ]] ; do
for (( i=1; i<=throttle; i++ )); do
jID=${JobIDArray[i]}
if ! kill -0 %$jID; then
wait %$jID
return=$?
iNext=$((iNext+1))
./child $iNext &
JobIDArray[i]=`jobidfromstring $(jobs %%)`
echo "$jID was returned. Its exits status was: $return | JobIDArray[$i] = ${JobIDArray[i]}"
fi
done
done
---------------------------
I am pretty much stuck at where to begin next. I am very new to bash and I don't even know if its possible to do what I want. My third script would work fine if I just had a way to identify if a job was terminated or not. I know that if you try to kill -s SIGCHLD the job when its terminated, it will give "no job exists" or something. I can't seem to know how I can get that to work in an IF statement. And if I did, would wait() still get the exit code.
