[Haskell-cafe] Re: -threaded
Maurício wrote: I see in the documentation and in many messages in this list that, if you want multithreading in your program, you need to use -threaded in ghc. Concurrency is supported just fine without -threaded. You need -threaded if you want to: 1) make foreign calls that do not block other threads 2) use multiple CPUs 3) write a multithreaded Haskell library or DLL Some library functions use foreign calls, for example System.Process.waitForProcess, so if you want to use them without blocking other threads you need -threaded. From an implementation perspective, -threaded enables OS-thread support in the runtime. Without -threaded, everything runs in a single OS thread. The features listed above all require multiple OS threads. Why isn't that option default? Does it imply some kind of overhead? There may be an overhead, because the runtime has to use synchronisation in various places. Hopefully the overhead is negligible for most things. It's not the default mostly for historical reasons, and because there are people who don't like to get multiple OS threads unless they ask for it. Also there are one or two things that don't work well with -threaded (Gtk2Hs, and System.Posix.forkProcess). Cheers, Simon ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: -threaded
Simon Marlow [EMAIL PROTECTED] writes: Concurrency is supported just fine without -threaded. You need -threaded if you want to: : 3) write a multithreaded Haskell library or DLL I thought -threaded (A.K.A. -smp, no?) only affected which runtime was used, and thus was a linking option. I do have a library that needs -smp, but as far as I knew, the onus would be on the *applications* to specify this when compiling/linking. Is that incorrect? Is there a way for a library to inform the application about this? -k -- If I haven't seen further, it is by standing in the footprints of giants ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: -threaded
Ketil Malde wrote: Simon Marlow [EMAIL PROTECTED] writes: Concurrency is supported just fine without -threaded. You need -threaded if you want to: : 3) write a multithreaded Haskell library or DLL I thought -threaded (A.K.A. -smp, no?) only affected which runtime was used, and thus was a linking option. I do have a library that needs -smp, but as far as I knew, the onus would be on the *applications* to specify this when compiling/linking. Is that incorrect? Is there a way for a library to inform the application about this? Sorry, I was a bit ambiguous there: for case (3) I mean a Haskell library that you intend to call from C, or some other foreign language, using multiple OS threads. You're absolutely right that for a Haskell library that you intend to call from Haskell, the -threaded option is used when the final program is linked, there's no way for the library itself to add it. Cheers, Simon ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
