#!/bin/sh
# ensure that tail -F handles rotation

# Copyright (C) 2009-2014 Free Software Foundation, Inc.

# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.

# This program 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 General Public License for more details.

# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.

if test "$VERBOSE" = yes; then
  set -x
  tail --version
fi

. "${srcdir=.}/tests/init.sh"; path_prepend_ ./src

check_tail_output()
{
  local delay="$1"
  grep "$tail_re" out > /dev/null ||
    { sleep $delay; return 1; }
}

# Wait up to 25.5 seconds for grep REGEXP 'out' to succeed.
grep_timeout() { tail_re="$1" retry_delay_ check_tail_output .1 8; }

# For details, see
# http://lists.gnu.org/archive/html/bug-coreutils/2009-11/msg00213.html

cleanup_fail()
{
  cat out
  warn_ $1
  kill $pid
}

# Perform at least this many iterations, because on multi-core systems
# the offending sequence of events can be surprisingly uncommon.
for i in $(seq 50); do
    echo $i
    rm -f k x out

    # Normally less than a second is required here, but with heavy load
    # and a lot of disk activity, even 20 seconds is insufficient, which
    # leads to this timeout killing tail before the "ok" is written below.
    >k && >x || framework_failure_ failed to initialize files
    timeout 60 tail -F k > out 2>&1 &
    pid=$!

    echo b > k;
    # wait for b to appear in out
    grep_timeout 'b' || { cleanup_fail 'failed to find b in out'; break; }

    mv x k
    # wait for tail to detect the rename
    grep_timeout 'tail:' || { cleanup_fail 'failed to detect rename'; break; }

    echo ok >> k
    # wait for "ok" to appear in 'out'
    grep_timeout 'ok' || { cleanup_fail 'failed to detect echoed ok'; break; }

    kill $pid
done

wait
Exit $fail