contrib/builddeb

fsmonitor: acquire localrepo.wlock prior to emitting hg.update state

we see some weird things in the watchman logs where the mercurial
process is seemingly confused about which hg.update state it is publishing
through watchman.

On closer examination, we're seeing conflicting pids for the clients involved
and this implies a race.

To resolve this, we extend the wlock around the state-enter/state-leave
events that are emitted to watchman.

Test Plan:
Some manual testing:

In one window, run this, and then checkout a different rev:

```
$ watchman -p -j <<<'["subscribe", "/data/users/wez/fbsource", "wez", {"expression": ["name", ".hg/updatestate"]}]'
{
    "version": "4.9.0",
    "subscribe": "wez",
    "clock": "c:1495034090:814028:1:312576"
}
{
    "state-enter": "hg.update",
    "version": "4.9.0",
    "clock": "c:1495034090:814028:1:312596",
    "unilateral": true,
    "subscription": "wez",
    "metadata": {
        "status": "ok",
        "distance": 125,
        "rev": "a1275d79ffa6c58b53116c8ec401c275ca6c1e2a",
        "partial": false
    },
    "root": "/data/users/wez/fbsource"
}
{
    "root": "/data/users/wez/fbsource",
    "metadata": {
        "status": "ok",
        "distance": 125,
        "rev": "a1275d79ffa6c58b53116c8ec401c275ca6c1e2a",
        "partial": false
    },
    "subscription": "wez",
    "unilateral": true,
    "version": "4.9.0",
    "clock": "c:1495034090:814028:1:312627",
    "state-leave": "hg.update"
}
```

Tailed the watchman log file and looked for invalid state assertion errors,
then ran my `rebase-all` script to update/rebase all of my heads.

Didn't trigger the error condition (but couldn't reliably trigger it previously
anyway), and the output captured above shows that the states are being emitted
correctly.

#!/bin/sh -e
#
# Build a Mercurial debian package from the current repo
#
# Tested on Jessie (stable as of original script authoring.)

. $(dirname $0)/packagelib.sh

BUILD=1
CLEANUP=1
DISTID=`(lsb_release -is 2> /dev/null | tr '[:upper:]' '[:lower:]') || echo debian`
CODENAME=`lsb_release -cs 2> /dev/null || echo unknown`
DEBFLAGS=-b
while [ "$1" ]; do
    case "$1" in
    --distid )
        shift
        DISTID="$1"
        shift
        ;;
    --codename )
        shift
        CODENAME="$1"
        shift
        ;;
    --cleanup )
        shift
        BUILD=
        ;;
    --build )
        shift
        CLEANUP=
        ;;
    --source-only )
        shift
        DEBFLAGS=-S
        ;;
    * )
        echo "Invalid parameter $1!" 1>&2
        exit 1
        ;;
    esac
done

trap "if [ '$CLEANUP' ] ; then rm -r '$PWD/debian' ; fi" EXIT

set -u

if [ ! -d .hg ]; then
    echo 'You are not inside a Mercurial repository!' 1>&2
    exit 1
fi

gethgversion
debver="$version"
if [ -n "$type" ] ; then
    debver="$debver~$type"
fi
if [ -n "$distance" ] ; then
    debver="$debver+$distance-$CODENAME-$node"
elif [ "$DEBFLAGS" = "-S" ] ; then
    # for building a ppa (--source-only) for a release (distance == 0), we need
    # to version the distroseries so that we can upload to launchpad
    debver="$debver~${CODENAME}1"
fi

control=debian/control
changelog=debian/changelog

if [ "$BUILD" ]; then
    if [ -d debian ] ; then
        echo "Error! debian control directory already exists!"
        exit 1
    fi

    cp -r $PWD/contrib/debian debian

    sed -i.tmp "s/__VERSION__/$debver/" $changelog
    sed -i.tmp "s/__DATE__/$(date --rfc-2822)/" $changelog
    sed -i.tmp "s/__CODENAME__/$CODENAME/" $changelog
    rm $changelog.tmp

    # remove the node from the version string
    SRCFILE="mercurial_$(echo $debver | sed "s,-$node,,").orig.tar.gz"
    "$PWD/hg" archive $SRCFILE
    mv $SRCFILE ..
    debuild -us -uc -i -I $DEBFLAGS
    if [ $? != 0 ]; then
        echo 'debuild failed!'
        exit 1
    fi

fi
if [ "$CLEANUP" ] ; then
    echo
    OUTPUTDIR=${OUTPUTDIR:=packages/$DISTID-$CODENAME}
    mkdir -p "$OUTPUTDIR"
    find ../mercurial*.deb ../mercurial_*.build ../mercurial_*.changes \
          ../mercurial*.dsc ../mercurial*.gz \
          -type f -newer $control -print0 2>/dev/null | \
      xargs -Inarf -0 mv narf "$OUTPUTDIR"
    echo "Built packages for $debver:"
    find "$OUTPUTDIR" -type f -newer $control -name '*.deb'
fi