From: Matt Armstrong <matt@...>
Date: 2002-12-15T04:46:47+09:00
Subject: Re: Ruby BUG when using PStore and fork

Jeremy Henty <jeremy@chaos.org.uk> writes:

> In article <873cp128ap.fsf@squeaker.lickey.com>, Matt Armstrong wrote:
>> ahoward <ahoward@fsl.noaa.gov> writes:
>> 
>>> i have gotten around this problem by spawning another process using
>>> the unix at command with a time of 'now'
>> 
>>     system("thecommand &")
>
> This doesn't solve the problem, which was that the child process
> inherits a lock on the pstore archive.

After experimenting, there is a way to close the PStore file in the
child process in ruby 1.7.

This program demonstrates it.  In a PStore transaction, it forks a
child that just loops 5 times printing a message, sleeping between.
Without the call to close_extra_files, the child blocks the parent's
2nd attempt to start a transaction.  With the call, it ends up closing
the PStore file it inherits from its parent and allows the parent to
open the PStore file again.

Unfortunately, I don't know a way to close file descriptors 3-1024 in
ruby 1.6.


require 'pstore'
store = PStore.new('pstore.test')

def close_extra_files
  3.upto(1024) { |i|
    begin
      File.open(i).close
    rescue Errno::EINVAL
    end
  }
end

store.transaction { |ps|
  puts "parent forking child"
  fork {
    close_extra_files
    5.times {
      sleep(1)
      puts "child is alive"
    }
    exit!
  }
}

puts "parent trying for second transaction"
store.transaction { |ps|
  puts "parent got second transaction"
}

Process.wait