From: Steve Lumos <slumos@...>
Date: 2002-01-17T17:16:38+09:00
Subject: Re: [RCR] #59 Add fsync method to IO class

matz@ruby-lang.org (Yukihiro Matsumoto) writes:

> Hi,
> 
> In message "[RCR] #59 Add fsync method to IO class"
>     on 02/01/17, Leslie Hensley <hensleyl@papermountain.org> writes:
> 
> |Adding fsync and fdatasync methods to the IO class will allow Ruby to
> |be used to address problem domains where it must be guaranteed that
> |data has been written to the disk. Examples of these are logging for
> |security purposes and transactional systems. The posix functions fsync
> |and fdatasync guarantee that any data that the OS is buffering for a
> |file is written to disk. This is distinct from IO#sync= which only
> |addresses if Ruby buffers the data above the OS level. As for
> |portability concerns, these methods seem just as reasonable as
> |IO#fcntl.
> 
> My concerns are:
> 
>   * how common are they?
>   * what if it's not defined on the platform?
> 
> 							matz.

I think fsync() is old POSIX and should be in every *nix.  fdatasync()
is part of realtime extensions in more recent POSIX and doesn't exist
everywhere (not on FreeBSD, seems to be the same as fsync() on Linux
(though I'm not a Linux person, and on Solaris 8 you have to define
_XOPEN_REALTIME and link with librt to get it).

  DESCRIPTION
     The fdatasync() function forces  all  currently  queued  I/O
     operations  associated  with  the  file  indicated  by  file
     descriptor fildes to the synchronized I/O completion state.

     The functionality is as described for  fsync(3C)  (with  the
     symbol _XOPEN_REALTIME defined), with the exception that all
     I/O operations are completed as defined for synchronised I/O
     data integrity completion.

and that sounds to me like it should be rb_notimplemented if it's not
defined instead of passed-off to fsync() (let the Ruby code decide to
use fsync() instead if that's really good enough.

Also, the whole point of these functions is to get the file in a known
state.  If they fail then the file probably isn't in the known state
which means that the return value should be checked and rb_sys_fail()
on error IMO.

Steve