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#
# Copyright (c) 2005 XenSource Ltd.
#
# This library is free software; you can redistribute it and/or
# modify it under the terms of version 2.1 of the GNU Lesser General Public
# License as published by the Free Software Foundation.
#
# This library is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
# Lesser General Public License for more details.
#
# You should have received a copy of the GNU Lesser General Public
# License along with this library; if not, write to the Free Software
# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
#
#
# Serialisation
#
LOCK_SLEEPTIME=1
LOCK_SPINNING_RETRIES=5
LOCK_RETRIES=10
LOCK_BASEDIR=/var/run/xen-hotplug
claim_lock()
{
local lockdir="$LOCK_BASEDIR/$1"
mkdir -p "$LOCK_BASEDIR"
_claim_lock "$lockdir"
}
release_lock()
{
_release_lock "$LOCK_BASEDIR/$1"
}
_claim_lock()
{
local lockdir="$1"
local owner=$(_lock_owner "$lockdir")
local retries=0
while [ $retries -lt $LOCK_RETRIES ]
do
mkdir "$lockdir" 2>/dev/null && trap "release_lock $1; sigerr" ERR &&
_update_lock_info "$lockdir" && return
local new_owner=$(_lock_owner "$lockdir")
if [ "$new_owner" != "$owner" ]
then
owner="$new_owner"
retries=0
fi
if [ $retries -gt $LOCK_SPINNING_RETRIES ]
then
sleep $LOCK_SLEEPTIME
else
sleep 0
fi
retries=$(($retries + 1))
done
_steal_lock "$lockdir"
}
_release_lock()
{
trap sigerr ERR
rm -rf "$1" 2>/dev/null || true
}
_steal_lock()
{
local lockdir="$1"
local owner=$(cat "$lockdir/owner" 2>/dev/null || echo "unknown")
log err "Forced to steal lock on $lockdir from $owner!"
_release_lock "$lockdir"
_claim_lock "$lockdir"
}
_lock_owner()
{
cat "$1/owner" 2>/dev/null || echo "unknown"
}
_update_lock_info()
{
echo "$$: $0" >"$1/owner"
}
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