[GHC] #10205: On Windows ghc-pkg always reports cache out of date

[GHC]

#10205: On Windows ghc-pkg always reports cache out of date
-------------------------------------+-------------------------------------
        Reporter:  hgolden           |                   Owner:  thomie
            Type:  bug               |                  Status:  patch
        Priority:  normal            |               Milestone:  7.10.2
       Component:  ghc-pkg           |                 Version:  7.10.1
      Resolution:                    |                Keywords:
Operating System:  Windows           |            Architecture:
 Type of failure:  Incorrect result  |  Unknown/Multiple
  at runtime                         |               Test Case:
      Blocked By:                    |                Blocking:
 Related Tickets:                    |  Differential Revisions:  Phab:D990
-------------------------------------+-------------------------------------

Comment (by Austin Seipp <austin@…>):

 In [changeset:"f0636562908236f6ce9bf91796bc952534074a61/ghc"]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="f0636562908236f6ce9bf91796bc952534074a61"
 Fix ghc-pkg reports cache out date (#10205)

 See Note [writeAtomic leaky abstraction].

 GHC on Linux already received a patch for this bug in
 e0801a0fb342eea9a312906eab72874d631271cf. On Windows several cabal tests
 were hitting the bug, causing validate failures, but we never noticed
 because of all the other tests that were failing on Windows. And it
 didn't start happening till `getModificationTime` received sub-second
 resolution support on Windows in
 5cf76186d373842bf64d49cecb09e0a9ddce3203.

 Since there are regression tests already, I am not adding another one.
 But for good measure, here is a script that shows the bug without
 needing to do a full validate run:

   DB=/tmp/package.conf.d.test
   GHC_PKG=ghc-pkg #utils/ghc-pkg/dist/build/tmp/ghc-pkg
   LOCAL_GHC_PKG="${GHC_PKG} --no-user-package-db --global-package-
 db=${DB}"
   while true; do
     rm -rf ${DB}
     ${LOCAL_GHC_PKG} init "${DB}"
     ${LOCAL_GHC_PKG} list
   done

 If you see "WARNING: cache is out of date" after a few seconds, the bug
 is not fixed.

 Reviewed By: austin

 Differential Revision: https://phabricator.haskell.org/D990

 GHC Trac Issues: #10205
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10205#comment:14>
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