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<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>GHC already garbage-collects threads that are blocked on an MVar
that is otherwise inaccessible (and hence cannot be updated).&nbsp; More precisely,
GHC sends the thread an asynchronous exception (ThreadBlocked or something), so
that it has a chance to clean up. <o:p></o:p></span></p>

<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p>&nbsp;</o:p></span></p>

<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>So perhaps the GC you want is already implemented?<br>
<br>
Simon<o:p></o:p></span></p>

<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p>&nbsp;</o:p></span></p>

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<p class=MsoNormal><b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>From:</span></b><span
style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>
haskell-bounces@haskell.org [mailto:haskell-bounces@haskell.org] <b>On Behalf
Of </b>Conal Elliott<br>
<b>Sent:</b> 24 December 2007 00:15<br>
<b>To:</b> haskell@haskell.org<br>
<b>Subject:</b> [Haskell] garbage collection of Concurrent Haskell threads?<o:p></o:p></span></p>

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<p class=MsoNormal><o:p>&nbsp;</o:p></p>

<p class=MsoNormal style='margin-bottom:12.0pt'>The classic paper &quot;The
Incremental Garbage Collection of Processes&quot; (<a
href="http://citeseer.ist.psu.edu/baker77incremental.html">http://citeseer.ist.psu.edu/baker77incremental.html</a>)
describes &quot;futures&quot; and how particularly garbage collecting them when
their pending result is no longer referenced.&nbsp; I've been playing with an
implementation of futures in Concurrent Haskell ( <a
href="http://haskell.org/haskellwiki/Reactive">http://haskell.org/haskellwiki/Reactive</a>),
using MVars, and I'm stumped about how to GC non-winning threads in a race
between futures (&quot;parallel or&quot;).&nbsp; I'm having winner kill loser,
which seems to work fine, though is potentially dangerous w.r.t locked
resources.&nbsp; Still, the elegance of a GC-based solution appeals to
me.&nbsp; Has anyone explored process GC ideas for Concurrent Haskell (or STM)?<br>
<br>
Futures are implemented using Concurrent Haskell's MVars.&nbsp; I first tried
using STM and TVars, simply using orElse to implement mappend for
futures.&nbsp; However, I didn't see how to avoid nesting
&quot;atomically&quot;, which yielded a run-time error.&nbsp; If anyone has
ideas about using STM &amp; TVars for futures, I'd love to hear. <br>
<br>
Thanks,&nbsp; - Conal<br>
<br>
<br>
<o:p></o:p></p>

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