From: Earle Clubb <eclubb@...>
Date: 2007-08-31T04:14:18+09:00
Subject: Changing date backward messes up threaded sleep

Can anyone explain this behavior?  If the system time is set backward,
the sleep method in the thread sleeps until the system clock has caught
back up to the original time.  The main thread does not display this
behavior.

The following script demonstrates the issue (run as root or sudo):
--------------------
#!/usr/bin/ruby -w

t = Thread.new do
  20.times do |i|
    puts "TH:#{Time.now}"
    sleep 1
  end
end

20.times do |i|
  puts "MN:#{Time.now}"
  sleep 1
  if i == 5
    now=Time.now
    now+=ARGV[0].to_f
    puts "Changing time to: #{now}"
    `date -s "#{now}"`
  end
end

t.join
--------------------

Running the script with and arg of -4 causes the thread to sleep for 5
seconds after the time change, but the main thread keeps on ticking
along.  An arg of +4 causes no problems.

Earle
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