#4391: forkIO threads do not properly save/restore the floating point
environment
---------------------------------+------------------------------------------
Reporter: draconx | Owner:
Type: bug | Status: new
Priority: normal | Milestone: 7.2.1
Component: Runtime System | Version: 6.12.3
Keywords: | Testcase:
Blockedby: | Difficulty:
Os: Unknown/Multiple | Blocking:
Architecture: x86_64 (amd64) | Failure: None/Unknown
---------------------------------+------------------------------------------
Comment(by rwbarton):
Replying to [comment:7 draconx]:
> Replying to [comment:6 rwbarton]:
> > It would be nice to mention in the documentation, maybe in section
"12.1.2.
> > GHC's interpretation of undefined behaviour in Haskell 98" under
"Unchecked
> > float arithmetic", that GHC does not manage the floating point
rounding or
> > exception registers in any way; in particular, they are not saved or
restored
> > by Haskell thread switches, and accessing them directly in conjunction
with
> > using built-in floating point operations causes undefined behavior.
>
> That would be a very unfortunate limitation as it goes well beyond
"don't use
> floating point in unbound threads".
But that's just the way it is, due to the types of the built-in floating
point operations not involving IO. For example, your program produces
different output ("A: True" on the last line) when compiled with `-O2`,
due to constant folding.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/4391#comment:9>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
_______________________________________________
Glasgow-haskell-bugs mailing list
[email protected]
http://www.haskell.org/mailman/listinfo/glasgow-haskell-bugs
