#4913: Make event tracing conditional on an RTS flag only
---------------------------------+------------------------------------------
Reporter: tibbe | Owner:
Type: feature request | Status: new
Priority: normal | Component: Runtime System
Version: 7.0.1 | Keywords:
Testcase: | Blockedby:
Os: Unknown/Multiple | Blocking:
Architecture: Unknown/Multiple | Failure: None/Unknown
---------------------------------+------------------------------------------
The current event tracing mechanism is enabled at link time by linking in
one of two different versions of a C function, one being a no-op function.
We could allow users to enable/disable tracing using a RTS flag instead,
making event logging more convenient to use. At the same time we would
introduce tracing levels.
Design:
Add a static memory location where the current tracing level is stored:
{{{
uint tracelevel = 0;
}}}
Modify `GHC.Exts.traceEvent` to read
{{{
foreign import ccall unsafe "&tracelevel" :: Ptr Word
traceEvent :: String -> IO ()
traceEvent msg =
if unsafePerformIO (peek tracelevel) > 0
then do
withCString msg $ \(Ptr p) -> IO $ \s ->
case traceEvent# p s of s' -> (# s', () #)
else return ()
}}}
and (optionally) add some more functions that log at different trace
levels.
This should be no slower than the current system. With inlining this
should result in a load and a branch at the call site. The load should be
cheap as the value is likely to be in cache (as it never changes). The
branch should be easy to predict as it's always the same. With some
cooperation from the code generator we could make sure that the branch is
always cheap.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/4913>
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
