From: Tanaka Akira <akr@...17n.org>
Date: 2002-09-28T02:55:59+09:00
Subject: [ruby-dev:18405] Re: pstore.rb can make a broken store

In article <200209271620.g8RGKtG02161@edge.back-street.net>,
  Takahiro Kambe <taca@back-street.net> writes:

> $B8E$/$O(BINN$B$+2?$+$N%a!<%j%s%0%j%9%H$@$C$?$H;W$$$^$7$?$,!"(BNetBSD($B$K8B$i$J(B
> $B$$$H;W$$$^$9$,(B)$B$N(Bfcntl(2)$B$K$"$j$^$7$?!#(B
> 
>      This interface follows the completely stupid semantics of AT&T System V
>      UNIX and IEEE Std 1003.1-1988 (``POSIX'') that require that all locks as-
>      sociated with a file for a given process are removed when any file de-
>      scriptor for that file is closed by that process.  This semantic means
>      that applications must be aware of any files that a subroutine library
>      may access.  For example if an application for updating the password file
>      ...
>      database.  Another minor semantic problem with this interface is that
>      locks are not inherited by a child process created using the fork(2)
>      function.  The flock(2) interface has much more rational last close se-
>      mantics and allows locks to be inherited by child processes.  Calling
>      flock(2) is recommended for applications that want to ensure the integri-
>      ty of their locks when using library routines or wish to pass locks to
>      their children.  Note that flock(2) and fcntl(2) locks may be safely used
>      concurrently.

$B$*$)!#(Bfcntl $B$rH/9T$7$?0J30$N(B file descriptor $B$G$bF1$8%U%!%$%k$K$D$J$,$C(B
$B$F$k$N$r(B close $B$9$k$H(B unlock $B$5$l$k$H$$$&$N$O3N$+$K4qL/$G$9$M!#$3$l$,(B
$BJQ$@$H$$$&$N$OG<F@$G$-$^$9!#(B

> flock(2)$B$NJ}$K$O!"(B
> 
> NOTES
>      Locks are on files, not file descriptors.  That is, file descriptors du-
>      plicated through dup(2) or fork(2) do not result in multiple instances of
>      a lock, but rather multiple references to a single lock.  If a process
>      holding a lock on a file forks and the child explicitly unlocks the file,
>      the parent will lose its lock.
> 
> $B$H$$$C$?5-=R$b$"$j$^$9!#%U%!%$%k$r(Bunlink(2)$B$9$k>l9g$O!":G8e$K%*!<%W%s(B
> $B$5$l$F$$$?%U%!%$%k5-=R;R$,(Bclose$B$5$l$?;~E@$G<BBN$,>C$($k$3$H$HBPHf$9$k(B
> $B$H!"6K$a$FIT<+A3$K;W$($^$9!#(B
> 
> > $B;W$&$K!"(Block $B$O(B fork $B$7$F$b<u$17Q$2$J$$$N$G!"(B3$B$D$N%F!<%V%k$N$&$A(B file
> flock(2)$B$O<u$17Q$2$^$9!#(B

$B;d$O(B file descriptor $B$K$D$/(B(close-on-exec $B$N$h$&$J(B)$B@-<A$@$H;W$$9~$s$G(B
$B$$$?$N$G(B fork $B$G$O<u$17Q$2$J$$$H;W$C$F$$$?$N$G$9$,!"<u$17Q$2$k$s$G$9(B
$B$M$'!#$^$5$K>e5-$N(B NOTE $B$NKAF,$G=R$Y$i$l$F$kOC$G!"FI$_J}$,B-$j$J$+$C$?(B
$B$G$9!#(B
-- 
[$BEDCf(B $BE/(B][$B$?$J$+(B $B$"$-$i(B][Tanaka Akira]
$B!V$U$($m(B! $B$o$+$a$A$c$s:n@o$G$9$(C"=$B!W(B(Little Worker, $B7KM7@84](B)