December 2005 - Haskell-Cafe

RE: [Haskell-cafe] Top-level TVars
by Simon Marlow 14 Dec '05

14 Dec '05

On 14 December 2005 10:11, Joel Reymont wrote: > I'm a bit lost in the discussion. Why do I need -fno-cse and how do I > seq at the top-level? > > On Dec 14, 2005, at 10:05 AM, Tomasz Zielonka wrote: > >> On Wed, Dec 14, 2005 at 10:03:42AM -0000, Simon Marlow wrote: >>> Well sure, but it's only a temporary problem. And you also have to >>> tell them to use {-# NOINLINE #-} and -fno-cse :-) >> >> -fno-cse is also neccesary? Oops, I didn't know that. Can I simply >> place it in {-# OPTIONS -fno-cse #-} ? Suppose you create two top-level IORefs with the same type, like this: var1 = unsafePerformIO $ newIORef 0 var2 = unsafePerformIO $ newIORef 0 GHC's CSE optimisation will common these up - after all, it's the same expression, so it must yield the same result, right? To turn this off, we use -fno-cse. It's good practice to use -fno-cse whenever you use top-level mutable objects of any kind. You can put it in the source file: {-# OPTIONS_GHC -fno-cse #-} at the top of your file. Cheers, Simon

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RE: [Haskell-cafe] killThread and FFI calls
by Simon Marlow 14 Dec '05

14 Dec '05

On 14 December 2005 15:35, Joel Reymont wrote: > On Dec 14, 2005, at 3:22 PM, Simon Marlow wrote: > >> On 14 December 2005 14:26, Joel Reymont wrote: >> >>> How does killThread work with FFI calls? What happens at the low >>> level when a thread is blocked on an FFI call and received a >>> KillThread exception? Does it exit immediately via some GHC magic or >>> is the exception caught when the FFI call returns? >> >> The latter. > > Does this change if I kill a thread that's blocked on I/O in a > threaded runtime? > > Does it get cleaned up immediately? A thread blocked on ordinary Handle-based I/O can be killed, because blocked Handle I/O is implemented using communication with the I/O manager thread, so it isn't an FFI call under the hood. Cheers, Simon

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RE: [Haskell-cafe] killThread and FFI calls
by Simon Marlow 14 Dec '05

14 Dec '05

On 14 December 2005 14:26, Joel Reymont wrote: > How does killThread work with FFI calls? What happens at the low > level when a thread is blocked on an FFI call and received a > KillThread exception? Does it exit immediately via some GHC magic or > is the exception caught when the FFI call returns? The latter. Cheers, Simon

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RE: [Haskell-cafe] Unbound threads and FFI
by Simon Marlow 14 Dec '05

14 Dec '05

On 14 December 2005 14:37, Joel Reymont wrote: > How do unbound threads play with FFI? According to Simon PJ, each > foreign call will get its own OS thread if its blocked. > > How does GHC determine if the call is blocked? Does each call get its > own OS thread from the start? Sometime later? When a thread exits Haskell to make an FFI call, another OS thread takes over running the other Haskell threads. If we don't have another OS thread available, we start one. > Does this depend on the safe/unsafe specs of the foreign call? this only happens for safe calls, not unsafe. > Does the above change if a threaded/non-threaded runtime is in use? this only happens in the -threaded RTS, in the non-threaded RTS a FFI call will block all the other Haskell threads. Cheers, Simon

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GHC internal error: traverse_weak_ptr_list: not WEAK
by Joel Reymont 14 Dec '05

14 Dec '05

loadtest: internal error: traverse_weak_ptr_list: not WEAK Please report this as a bug to glasgow-haskell-bugs(a)haskell.org, or http://www.sourceforge.net/projects/ghc/ Has anyone seen this before? I got this after running a 1,300 socket connections for a while (probably x3 threads overall). Any workarounds? Thanks, Joel -- http://wagerlabs.com/

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Unbound threads and FFI
by Joel Reymont 14 Dec '05

14 Dec '05

How do unbound threads play with FFI? According to Simon PJ, each foreign call will get its own OS thread if its blocked. How does GHC determine if the call is blocked? Does each call get its own OS thread from the start? Sometime later? Does this depend on the safe/unsafe specs of the foreign call? Does the above change if a threaded/non-threaded runtime is in use? Thanks, Joel -- http://wagerlabs.com/

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killThread and FFI calls
by Joel Reymont 14 Dec '05

14 Dec '05

Folks, How does killThread work with FFI calls? What happens at the low level when a thread is blocked on an FFI call and received a KillThread exception? Does it exit immediately via some GHC magic or is the exception caught when the FFI call returns? Thanks, Joel -- http://wagerlabs.com/

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Announcing Djinn, new version 2004-12-13
by Lennart Augustsson 14 Dec '05

14 Dec '05

There is a new version of Djinn available, with two notable new features: Haskell data types can be defined and the found functions are sorted (heuristically) to present the best one first. To play with Djinn do a darcs get http://darcs.augustsson.net/Darcs/Djinn or get http://darcs.augustsson.net/Darcs/Djinn/Djinn.tar.gz Then just type make. (You need a Haskell 98 implementation and some libraries.) And then start djinn. `-- Lennart

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RE: [Haskell-cafe] Re: Bringing Erlang to Haskell
by Simon Peyton-Jones 14 Dec '05

14 Dec '05

There's a (GHC-specific) Wiki page on concurrent programming in GHC, in the new GHC Wiki. http://hackage.haskell.org/trac/ghc/wiki/GhcConcurrency Feel free to add more info to it. I've dropped in the links below. Simon | -----Original Message----- | From: haskell-cafe-bounces(a)haskell.org [mailto:haskell-cafe-bounces@haskell.org] On Behalf Of | Robert Dockins | Sent: 13 December 2005 15:18 | To: Joel Reymont | Cc: Haskell-Cafe Cafe | Subject: Re: [Haskell-cafe] Re: Bringing Erlang to Haskell | | BTW, there has already been some work in this area. | | http://www-i2.informatik.rwth-aachen.de/~stolz/dhs/ | http://www.informatik.uni-kiel.de/~fhu/PUBLICATIONS/1999/ifl.html | | | _______________________________________________ | Haskell-Cafe mailing list | Haskell-Cafe(a)haskell.org | http://www.haskell.org/mailman/listinfo/haskell-cafe

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RE: [Haskell-cafe] Top-level TVars
by Simon Marlow 14 Dec '05

14 Dec '05

On 14 December 2005 09:57, Tomasz Zielonka wrote: > On Wed, Dec 14, 2005 at 09:51:16AM -0000, Simon Marlow wrote: >>> Here is an example how you can initialize a top-level STM variable. >>> http://www.uncurry.com/repos/TimeVar/TimeVar.hs >>> It just forks a new thread inside unsafePerformIO, it runs >>> "atomically" in it and passes the result through ordinary MVar. >> >> A cheaper way is just to seq the top-level TVar at the beginning of >> Main.main. > > Yes, I tried that approach. However, imagine telling users of > your library to do that in every program (withSocketsDo comes > to mind). Well sure, but it's only a temporary problem. And you also have to tell them to use {-# NOINLINE #-} and -fno-cse :-) Cheers, Simon

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