gistfile1.txt

claim_lock()
{
    mkdir -p "$LOCK_BASEDIR"
    _setlockfd $1
    # The locking strategy is identical to that from with-lock-ex(1)
    # from chiark-utils, except using flock.  It has the benefit of
    # it being possible to safely remove the lockfile when done.
    # See below for a correctness proof.
    local rightfile
    while true; do
        eval "exec $_lockfd<>$_lockfile"
        flock -x $_lockfd || return $?
        # We can't just stat /dev/stdin or /proc/self/fd/$_lockfd or
        # use bash's test -ef because those all go through what is
        # actually a synthetic symlink in /proc and we aren't
        # guaranteed that our stat(2) won't lose the race with an
        # rm(1) between reading the synthetic link and traversing the
        # file system to find the inum.  Perl is very fast so use that.
        rightfile=$( perl -e '
            open STDIN, "<&'$_lockfd'" or die $!;
            my $fd_inum = (stat STDIN)[1]; die $! unless defined $fd_inum;
            my $file_inum = (stat $ARGV[0])[1];
            print "y\n" if $fd_inum eq $file_inum;
                             ' "$_lockfile" )
        if [ x$rightfile = xy ]; then break; fi
        # Some versions of bash appear to be buggy if the same
        # $_lockfile is opened repeatedly. Close the current fd here.
        eval "exec $_lockfd<&-"
    done
}