Re: RFC: omit write barrier instructions unless '-threaded'

On 27/02/13 16:17, Joey Adams wrote:

On Sun, Feb 24, 2013 at 3:40 PM, Gabor Greif mailto:ggreif@gmail.com> wrote:

Hi all,

from what I gathered so far no emission of write barriers is needed when - running on a uniprocessor (-threaded or not) - running on a multiprocessor sans having linked with -threaded.

On Windows, the non-threaded RTS does I/O with forked threads; see rts/win32/IOManager.c and the async* functions in GHC.Conc.Windows. I think this means that for Windows, we need those write barriers even for non-threaded.

Windows does use multiple OS threads to do non-blocking I/O in the non-threaded RTS. However, it doesn't run multiple Haskell threads in parallel (the threaded RTS is needed for that), so Gabor's patch which just affects the update code is fine. If we did actually rely on the C write_barrier() macro for the Windows I/O manager, then there could be a problem, but we don't. On the other hand, it might be prudent to enable write_barrier() on Windows just in case someone tries to use it in the non-threaded RTS in the future. Cheers, Simon