From: "Ara.T.Howard" <ahoward@...>
Date: 2003-12-09T15:57:02+09:00
Subject: Re: RCR - 'struct flock*' wrapper for rb_io_fcntl

On Tue, 9 Dec 2003, Yukihiro Matsumoto wrote:

> Date: Tue, 9 Dec 2003 13:41:50 +0900
> From: Yukihiro Matsumoto <matz@ruby-lang.org>
> Newsgroups: comp.lang.ruby
> Subject: Re: RCR - 'struct flock*' wrapper for rb_io_fcntl
> 
> Hi,
> 
> In message "RCR - 'struct flock*' wrapper for rb_io_fcntl"
>     on 03/12/09, "Ara.T.Howard" <ahoward@ngdc.noaa.gov> writes:
> 
> |SYNOPSIS:
> |
> |  ruby's fcntl call is incomplete in that one cannot pass a 'struct flock *'
> |  arg as fcntl's third arg.  because of this, no posix compliant locking is
> |  available from within ruby.
> 
> You can use pack/unpack for the purpose.
> 
>   require 'fcntl'        # import constants, perhaps this replaces IO#fcntl... 
> 
>   f = open('/tmp/foobar', 'w')
>   flock = [Fcntl::F_RDLCK, 0, 0, 0, 0].pack("ssqqi")

is this guaranteed to work:

  are the offsets always the same as a struct flock* as the compiler lays them
  out?

if so, i am personally o.k with this. (thanks for the pointer!)


>   p Fcntl::F_RDLCK, Fcntl::F_GETLK
>   f.fcntl Fcntl::F_GETLK, flock
>   p flock.unpack("ssqqi")
> 
> But still I would not deny your proposal for the sake of readability
> and portability.  Maybe there can be functions that work similar to
> pack_sockaddr_*() / unpack_sockaddr_*() in the socket extension.
> pack_flock() or something.

yes that sounds good if anwser to above is 'yes'

-a
-- 

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