From: David Douthitt <DDouthitt@...>
Date: 2000-03-20T09:29:22-06:00
Subject: [ruby-talk:02034] class File acting funny!

I'd like to define a class Lock < File which would act like this:

   Lock.lock

   # do stuff....

   Lock.unlock

or even perhaps

   Lock.lock {

   #  do stuff

   }

or even

   Lock.lock("myfile") {

   # stuff

   }

Designing my own iterators isn't a problem, but this lock class seems to be.  I get many funny errors:

   * Lock.new insisted on 1 parameter - but initialize method had NO parameters
   * $0 was not being recognized in parameter default value expressions
   * print "foo" would generate: in 'write': not open for writing (IOError)
   * $stdio evaluates to nil
   * flock appears to fail on non-existant files (?) and says in the documentation "advisory" lock....

I might just throw this back into the Korn shell (called from ruby of course)

   set -o noclobber
   cat /dev/null 2> /dev/null > $1 && set +o noclobber

Here's what I have tried (with comments)

#!/opt/ruby/bin/ruby

class Lock < File
   attr_accessor :locked, :lockdir, :lockfile

   def initialize
      @locked = false
      @lockdir = "/var/spool/locks"
      @lockfile = @lockdir + "/" + File.basename($0) + ".lock"
   end

   def Lock.new
#     raise "Lockdir not set!" if @lockdir == nil;
      raise "\$0 not set?!" if $0 == nil;

      super ("/var/spool/locks" + "/" + File.basename($0) + ".lock", "w")
   end

   def unlock
      raise "Lockfile not set!" if @lockfile == nil;
      raise "Could not unlock!" if (File.unlink(@lockfile) == 1);
      @locked = false
   end

   def lock (lockf = lockfile)
      raise "Lockfile not set!" if @lockfile == nil;

# -- generates error:
# ./lock.rb:26:in `lock': Lockfile not set! (RuntimeError)
#         from ./lock.rb:63
#
# Even after initializing!! (self.initialize)

      @lockfile = lockf;

      raise "Could not lock!" if ! @lockfile.flock(LOCK_EX|LOCK_NB)
      @locked = true
   end

   def display_lock

#     print "Current lock:\n\n"
# -- generates this error:
#
# ./lock.rb:29:in `write': not opened for writing (IOError)
#         from ./lock.rb:29:in `print'
#         from ./lock.rb:29:in `display_lock'
#         from ./lock.rb:39

      p @locked;
      p @lockfile;
      p @lockdir;
   end
end

# mylock = Lock.new;
# -- generates this error:
#
# ./lock.rb:43:in `new': wrong # of arguments (0 for 1) (ArgumentError)
#         from ./lock.rb:43
#
# Even though Lock.initialize has no parameters!
# Yes, I know File.new has one.... but not calling File.new but Lock.new right?
# If I redefine Lock.new this problem goes away.... but
# what problems does it create?

mylock = Lock.new;

mylock.display_lock

mylock.lock

   mylock.display_lock

mylock.unlock
[....snip!....]

Also:

# ruby -v
ruby 1.4.3 (1999-12-08) [hppa1.1-hpux10.20]
# uname -a
HP-UX oursys B.10.20 A 9000/861 2016701434 two-user license
#

Thanks for all the help!