tests/testlib/wait-on-file

narrow: delegate the dirstate's narrow spec writing to the transaction

This make it more transactional and will help us to simplify their backup.

The implementation is not great, but it keep the patch simple as this is not the
time for a larger refactoring yet.

#!/bin/sh
#
# wait up to TIMEOUT seconds until a WAIT_ON_FILE is created.
#
# In addition, this script can create CREATE_FILE once it is ready to wait.

if [ $# -lt 2 ] || [ $# -gt 3 ]; then
    echo $#
    echo "USAGE: $0 TIMEOUT WAIT_ON_FILE [CREATE_FILE]"
fi

timer="$1"

# Scale the timeout to match the sleep steps below, i.e. 1/0.02.
timer=$(( 50 * $timer ))
# If the test timeout have been extended, also scale the timer relative
# to the normal timing.
if [ "$HGTEST_TIMEOUT_DEFAULT" -lt "$HGTEST_TIMEOUT" ]; then
    timer=$(( ( $timer * $HGTEST_TIMEOUT) / $HGTEST_TIMEOUT_DEFAULT ))
fi

wait_on="$2"
create=""
if [ $# -eq 3 ]; then
    create="$3"
fi

if [ -n "$create" ]; then
    touch "$create"
    create=""
fi
while [ "$timer" -gt 0 ] && !([ -e "$wait_on" ] || [ -L "$wait_on" ]) ; do
    timer=$(( $timer - 1))
    sleep 0.02
done
if [ "$timer" -le 0 ]; then
    echo "file not created after $1 seconds: $wait_on" >&2
    exit 1
fi