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From: Earl Chew <earl_chew@agilent.com>
Newsgroups: gmane.comp.sysutils.supervision.general
Subject: svwaitup races with sv
Date: Sun, 19 Jul 2009 10:14:31 -0700
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The script below generates the following output:

> down: ./svc: 0s
> svwaitup: warning: ./svc: is down.
> .... WaitUp 1
> Try again
> run: ./svc: (pid 8496) 2s, normally down, want down

It illustrates a race between runsv/sv and svwaitup.

Commenting out the "touch svc/down" leads to other strange
results like:

> run: ./svc: (pid 8651) 0s
> svwaitup: warning: ./svc: unable to change directory: file does not exist
> .... WaitUp 1
> Try again
> run: ./svc: (pid 8651) 4s, want down


The key is that sv(8) writes its command and simply exits. There is
no way to determine if the command has actually been acted upon.

For example, the following appears to synchronise ok but is a bit
clunky:

    rm svc/supervise/pid
    ../command/sv once ./svc
    while [ -e svc/supervise/pid ] ; do
      sleep 1
    done

It would be better if sv(8) itself could synchronise.

Earl

-----------------------------------------------------------------------

#!/bin/sh

rm -rf svc
mkdir svc

touch svc/down

cat > svc/run <<\EOF
#!/bin/sh

sleep 30
EOF
chmod +x svc/run

trap 'kill $SVC_' EXIT
../command/runsv ./svc &
SVC_=$!

../command/sv once ./svc
../command/sv status ./svc || echo .... Status $?
../command/svwaitup ./svc  || echo .... WaitUp $?

sleep 2
echo "Try again"

../command/sv status ./svc || echo .... Status $?
../command/svwaitup ./svc  || echo .... WaitUp $?