[commit: ghc] master: Add TODO about getMonotonicNSec() wrapping that can no longer happen. (9bf6310)

[git at git.haskell.org]

Repository : ssh://git@git.haskell.org/ghc

On branch  : master
Link       : http://ghc.haskell.org/trac/ghc/changeset/9bf6310d2002ef57dc726a4d9240bd520925114d/ghc

>---------------------------------------------------------------

commit 9bf6310d2002ef57dc726a4d9240bd520925114d
Author: Niklas Hambüchen <mail at nh2.me>
Date:   Wed Sep 27 15:24:11 2017 -0400

    Add TODO about getMonotonicNSec() wrapping that can no longer happen.
    
    Knowing this is important for followup commits, where we will subtract
    getProcessElapsedTime() values from each other, in a way that assumes
    that there is no wrapping every 49 days.
    
    Reviewers: bgamari, austin, erikd, simonmar, NicolasT
    
    Reviewed By: bgamari
    
    Subscribers: rwbarton, thomie
    
    GHC Trac Issues: #14233
    
    Differential Revision: https://phabricator.haskell.org/D3964


>---------------------------------------------------------------

9bf6310d2002ef57dc726a4d9240bd520925114d
 rts/win32/GetTime.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/rts/win32/GetTime.c b/rts/win32/GetTime.c
index 90c0d0d..014a676 100644
--- a/rts/win32/GetTime.c
+++ b/rts/win32/GetTime.c
@@ -84,6 +84,11 @@ getMonotonicNSec()
     }
     else // fallback to GetTickCount
     {
+        // TODO: Remove this code path, it cannot be taken because
+        // `QueryPerformanceFrequency` cannot fail on Windows >= XP
+        // and GHC no longer supports Windows <= XP.
+        // See https://ghc.haskell.org/trac/ghc/ticket/14233
+
         // NOTE: GetTickCount is a 32-bit millisecond value, so it wraps around
         // every 49 days.
         DWORD count = GetTickCount();