patch applied (ghc-6.8/ghc): Move file locking into the RTS, fixing #629, #1109

[Ian Lynagh]

Tue Nov 20 06:08:59 PST 2007  Simon Marlow <simonmar at microsoft.com>
  * Move file locking into the RTS, fixing #629, #1109
  File locking (of the Haskell 98 variety) was previously done using a
  static table with linear search, which had two problems: the array had
  a fixed size and was sometimes too small (#1109), and performance of
  lockFile/unlockFile was suboptimal due to the linear search.
  Also the algorithm failed to count readers as required by Haskell 98
  (#629).
  
  Now it's done using a hash table (provided by the RTS).  Furthermore I
  avoided the extra fstat() for every open file by passing the dev_t and
  ino_t into lockFile.  This and the improvements to the locking
  algorithm result in a healthy 20% or so performance increase for
  opening/closing files (see openFile008 test).

    A ./includes/FileLock.h
    M ./rts/Hash.c -6 +3
    M ./rts/Hash.h +7
    M ./rts/Linker.c +2
    M ./rts/RtsStartup.c +11
    A ./rts/posix/FileLock.c